11:33 -- The circular ring is connected to a constant voltage (V+), so it's at AC ground. It prevents signals in other parts of the circuit from affecting the voltage of the disc inside the ring. (It's a "guard ring".) The transistor's collector (C) is connected to this ring / AC ground. The disc inside the ring is connected to the transistor's base (B). The S-shaped piece of PCB that's connected to the transistor's emitter (E) is a section of transmission line, which resonates at a particular frequency and which determines the circuit's frequency of oscillation. Since one end of the S-shaped piece of PCB is connected to the transistor's emitter (E), which is the signal source, and since the other end of the S-shaped piece of PCB is connected to capacitors which are connected to ground (so that the far end of the S-shaped strip is at AC ground), then the S-shaped strip is a 1/4 wavelength resonant section of transmission line. There is feedback between transistor's base (B) and its emitter (E) through the space between the short strip of PCB ("stub") that's connected to B and the section of the S-shaped piece of PCB that's connected to E. The size of the space between that stub and the S-shaped piece of PCB that's connected to E largely determines the degree of coupling (feedback) between the transistor's base and emitter. The longer the space or the narrower the space, the greater the coupling / feedback. So the circuit is a one transistor oscillator (specifically, a grounded-collector oscillator), having a resonant circuit that's connected to the transistor's emitter, and having some coupling / feedback between its emitter and base.
@@therealjamespickering -- The circuit generates microwaves. The microwaves are radiated by the little antenna. When something moves through the field of microwaves, some of the microwaves are the reflected to the antenna, where the reflected signal is absorbed, amplified, and combined with some of the microwaves being generated by the circuit. The result is a small change in the circuit's normal voltages, which the rest of the circuit (the rectangular chip) then detects.
@@kevinbyrne4538 Ok, that's much clearer, thank you! So the S-shaped track oscillates at a frequency of 3.18 GHz and the interaction between this and the disk attached to the base results in a certain voltage to be passed through the emitter? Movement in the room would then result in variations in the voltage? Does the board only output a high/low digital signal, or is it an analogue signal that could be used to determine something about the size/velocity of the object?
@@N1gel Haha, I don't even know the basics of electronics, but I get drawn into these. I at least have an idea of which components do what, it's just the whys that Confused me, lol. My list of questions never ends and at some point I will know more, but right now, I still love Clive's vids despite my lack of knowledge...the big surprise I was getting at you know, lol.
@@watsoft70 Glad to know I'm not the only electronics-noob in the audience. Whenever he talks about complicated circuits like this, I'm lucky if I can even follow along half of what's going on.
@@N1gel ... some things are just beyond the ken of mere mortals, and are not meant to be known the wot of. Microwave RF is clearly for wizards and other ethereal beings.
The Concentric Circles thing is the actual Antenna Element Back Plane . The Squiggle Line Track simply a Load Inductor doubling as the Antenna. If you measure the Distance between the Squiggle Track folding back on it's self you will find it a fraction of the actual operating frequency in .wavelength.. Probably 1/8th or 1/4 wavelength.
The rectangular track on the base pin will probably be 1/4 wave resonant stub too. Don't forget to account for velocity factor when working out the frequency, which is approx 0.5 on FR4.
Argh. I should read more before posting. If you think of it as a delay line one end is the frequency of the oscillator right now and the other end is the frequency of the oscillator a few pico seconds ago.
Hehe, I also made those “simple” (slightly illegal) FM transmitters when I was young, most often with a preceding microphone amplifier, to become a small bugging device. Often choosing close to 88MHz or 108MHz, and then any ordinary FM-radio (preferably small and hand held) could be used as receivers. I learned then, that there was a big complexity to RF-electronics, since I put a lot of effort in doing very nice and clean builds, with often no good results, while a class mate made a very “ugly” build (blobby soldering, wires not cut close to the PCB etc) and that worked better than any of the rest of the class mates. It’s fantastic that a simple circuit like that actually ends up as a FM-transmitter. The simplicity to build things like this for FM an AM, together with the avast amount of existing equipment, is actually why I feel a bit “scared” that DAB will “destroy” the possibilities for future young kids, interested in electronics, to test and learn in an exiting (slightly illegal) way. Of course you can do a lot of MUCH cooler things today, with all sorts of micro controllers and advanced chips, sensors etc, but not at the same low level. I’m glad Sweden postponed the switch to DAB. It really feels meaningless, since you could get the digital feeds via mobile data streams and the cost to switch all existing analog equipment would be enormous. It have played out it’s role... Keep at least some of the current FM-band analog (as well as the AM-band) as a backup system and for the kids to play with ;) Btw, we soldered the antenna (normally measured to a quarter to the wavelength) to one of the loops of the wounded inductor.
If Clive says it's complex it's really complex. Another really interesting video Clive thanks for all the hard work you put into these. Glad I stumbled on your channel many moons ago, it fascinates me how all these things work and makes me want to get into making a few projects myself
Loved this video! The fact that you tried to comprehend the magic of RF and still put out this video - the transparent film screen showing the back was a great way for you to explain of your thought train in a very slick way!. Always look forward to your new content, I’m pretty sure I’ve watched all your back catalogue :-D
A hybrid coupler in ring configuration ("rat race coupler") perhaps. These couplers typically have four ports. Power input at port 1 splits and travels both ways round the ring. At ports 2 and 3 the signal arrives in phase and at port 4 it's out of phase and cancels. The reflected, out of phase signal (from your body) can be made to "unbalance" the ring which effectively brings one port to a higher potential than the other ports. Those eclipsed portions of ring might be the port couplings. Just a guess- I am not a µwave engineer (but have played with transmission lines in the past).
I like it and me too. C band satellite LNB pre amps when 120$ was entry price for a single NEC transistor with a much improved noise figure. Had no real business ordering those and resurrecting dead ones from lightning surges, but I was still more successful than not. Only thing I can recognize here is the quarter wave tank described as the only rectangular item on the board, hanging off the collector. 14:06 Those were very commonly used in that field for side by side coupling of the mixer signals. CRS about too much of it these days, but we are talking mid 80s too. End of the day, way too pricey for me to play and win.
This reminds me of a gadget I built before touch sensors existed. I used a PIC to generate PWM into a coil, which coupled with another coil. Somehow I could measure the phase between coils, which I put through an op-amp and back into the PIC. The theory was that my finger would change the phase. They laughed at me, said it can't work, but it did! I put two of these in a box and by sliding my finger up and down on the surface, I controlled a PWM fluorescent dimmer. Happy memories. My goal was to make a water-proof switch.
That's how inventions are made. Though a waterproof switch is much simpler to make, just get a reed switch and a magnet. That's how Nikko did their submarines.
Before touch sensors were around? Seriously? How about 1978 when I made touch sensors using CMOS 4011's? PIC's didn't even exist then. The circuit was simple, touch one spot to turn on and the other spot to turn off. Have to say though, the capacitance coupled sensor would definitely be better and could be made waterproof.
Clive, as a 50+ y/o electronics and radio enthusiast, may I say, if your video's were available when I was doing my training, I would be "up there" now, I really enjoy all your "tear-downs" and the way you detail your explanations. They come across so well. Even something like this complex uWave circuit. Well done.... You're a top bloke!
Sometimes I wonder what effect it would have had on my own learning if RUclips had been around when I was young. It'll be interesting to see how it affects the current generation. They have a lot of technical materials and tools at their disposal.
@@bigclivedotcom Yea, I'm so envious! One of my first "serious" books was a Ladybird book Making a Transistor Radio when I was about 10 - Remember the OC71?
I think this is a voltage controlled oscillator, it doesn’t use a fixed frequency. As others have said, the circular elements on the back plane are part of the antenna. For this sort of circuit to work the antenna needs to have an outrageously high Q, and ideally a pretty low radiation resistance, which a loop antenna provides. Essentially the ring looks to be a loop antenna acting mostly as a receive antenna. It’s coupled to to the transmit antenna with a sort of hybrid between a gamma match and a Patterson loop style capacitive network. The 1k resistor and the two adjacent capacitors right before the sense input are an RC pi filter tuned to the oscillator’s stable frequency. When the environment around the sensor changes, the amount of reflected power and the phase of the received signal changes slightly, which causes a change in the circulating current in the receive loop, which causes the complex impedance on the oscillator output to change, which changes the oscillator’s frequency. The frequency change means the signal will move relative to the pass band on the RC pi network, changing the attenuation of the signal and altering the voltage at the sense pin, and the chip just triggers on the change. If you have an RTL-SDR dongle or similar you should be able to confirm this by watching the signal in the waterfall. I bet it swings like mad when you sweep your hand near the sensor. Clive, if you don’t have an SDR handy, I’ll order a couple and put it on the spectrum analyzer, and I’ll also send you a little SDR dongle. Super handy little gadgets for poking at RF circuits like this.
Indeed there's a github repo with information about this module (jdesbonnet/RCWL-0516) which mentions: "finally found the signal at 3.181GHz with the HackRF One SDR! One interesting observation: waving my hand in front of the sensor causes significant changes in the transmitting frequency, shifting by up to 1MHz"
Matthijs van Duin that’s interesting, I would actually expect the swing to be much bigger for it to be based on the changing attenuation of the band pass filter. 1MHz swing on a 3GHz signal would probably only be a fraction of a dB even at the steepest part of the filters curve. I wonder if it’s using the op amp that’s on the input of the chip as a phase comparator or something similar.
Hi Bigclive - really interesting video - I remember UHF/Microwave construction being described to me in the late 1970s as a bit like "plumbing" - the usual headache when designing higher and higher frequency circuits was trying to overcome and eliminate stray capacitance, but as you get towards the top end, they stop being a "problem" and start becoming an "enabler" - but you instinctively realise that :) What's more interesting to see is that (compared to the tolerances within microchip fabrication) the relatively crude technology behind copper etching can be used to great effect. It's a bit like looking at plans for a fairly crude valve amplifier and realising that the "cleverness" is all down to the physical construction, which we've all kind of forgotten with the ability to cram more and more components into an ever decreasing space to overcome design flaws This is a perfect example of less being very much more :)
I was a broadcast engineer for a couple of decades, but RF was never my strong suit. I could keep big transmitters running, but I was way more comfortable with studio gear and computer stuff. I totally understand what you're saying!
I bet it's the same ghost that switched my grandmas stove on and ran my water heater for 4 days straight. If you manage to catch it, make sure it can't hurt anyone again.
The feedback from the collector to the base is in the transistor, mainly the internal capacitance between the collector and emitter. The square trace connected to the base is less an inductor/capacitor and more a delay line. The oscillator operates as a common base amplifier. The "squiggly" emitter line is a delay line. The disk of copper on the bottom behind the transistor is simply a ground plane. Some capacitance is there but it's unintentional. The ring of copper is the actual antenna. The ring and the disk ground plane act like a fresnel lens and makes the radar output more like a dipole antenna. When you move towards or away from the antenna, not only do you cause a doppler shift but you mainly case the frequency to shift (you're now part of the tuned circuit. At cm waves both are pretty much the same thing). The wiggly part of the emitter track introduces a delay from the frequency a few pico seconds ago and mixes it with the frequency that's happening now. In phase oscillations use less current than out of phase oscillations. The increased current drain for an out of phase signal is dropped and filtered by the emitter resistor (which is where the real feedback and transmit occurs) and the associated emitter/ground capacitors for detection.
@@pahom2 Everything is an antenna. In your case the dual squiggly lines is probably being used as an antenna and phase comparator. Remember that at these frequencies there is no real tuning inductor or tuning capacitor. Everything (including you) is part of a tuned circuit.
The ring is a resonator at wavelength equal to its circumference. The top of the ring is pinned firmly to VCC by those bypass capacitors forcing that to be an E field node and the bottom to be an anti-node. The collector and emitter have opposite phase so that the meander line couples to the resonator on the back. Do those two vias on the disk connect to the base? They seem to be about -120/240 degrees away from the top standing wave node. Combined with the transistor characteristics and the base capacitor overlap, I predict this brings the positive feedback into phase with the resonator. Any Doppler effect shift will be f0 (v/c). That disk might couple to reflected energy so that the same transistor mixes those two signals with the 1k -- 1 nF forming the LPF to reject the carrier and sum frequencies.
not sure if it was intended as part of the joke, but arthur c clarke was a radar specialist in WWII so I don't think microwave tech was very magical to him.
This break-down caused me to realize that not every part of a circuit is either positive or negative relative to a connected part; but rather, the relationship can be more complicated; time-based or based on detection/externalities.
Back in electronics school, my teacher had been a elec tech for radios in fighter jets. He told the story of a jet that would have radio troubles. After some time of trying to figure it out,, the E7 boss man, handed him a can of polish, and told him to polish the inside of the box the radio sat in... It seems that the box was a capacitor in the circuit. ... hmmm Well, the polishing worked,,, at least that is what we were told... Thanks and keep up the good work.
I at one time worked on 45w 850mHz transmitters at the factory. I would tune the circuits be adding or removing silver solder from the copper patterns on the board. They were very sensitive to anything being moved around the power transistors.
@@stargazer7644 Not really. A 850mHz antenna is only about 6 inches long. These were for a early car phone system base station, before cellular phones.
@@oldmgbs2 - Star Gazer is busting your chops a little, for using the 'milli' prefix when you (presumably) intended the 'mega' prefix -- because a sub-1Hz frequency would (of course) need a hella large antenna :-)
Make sure and redesign your room to be the right size resonant cavity faraday cage. Make sure it is grounded. There, now your idea would work, but the sound of people screaming from sudden blindness would be your early warning alarm...
That RF oscillator could be used as the volume oscillator in a theremin. It would be interesting to attach an oscilloscope to the 'sense' point and see how sensitive it is. I might buy some of these and try to build a theremin.
Im only a low level entry into RF circuits but I am aware in microwave frequencies an antenna called a discone is used most common. They tend to use a capacitive 'hat' and obviously get smaller the higher the frequency, so I think you have a very squashed discone antenna with all the relevant coupling components. The idea with RF is you want as much power thrown out as possible without any RF reflecting back down the feed to the transmitter or damage will occur. I know its very critical with high power outputs, but not so sure with very low power like this but it could have an effect if not controlled properly. It is called a discone because that is exactly what it looks like, a disc on a cone with an insulated separator between them. The disc is fed with RF and the cone is the ground reference and the size and angle relationship ( radius of disc and angle/length of cone with solid cone and disc or using rods as a cone and disc ) between them determines the frequency you want to transmit at. As mentioned by another commenter further down the receive parameters of the antenna will usually be compromised by a fraction of the desired transmit frequency ie 1/2 wave, 1/4, 1/8, 3/8 etc are typical because of size limitations on the board or your available space at home because the actual size required for a 1:1 transmitter in most cases would be far greater than the space available. Reception through an antenna does not need to bother so much with sizes of things as all it does is alter the amount of energy/noise/interference available to be received. In short, the antenna length/size must be a fraction of the wavelength of the frequency you wish to transmit at and the load on the transmitter device should be as close to 50 ohms as possible to prevent a dead short, because transmitting RF is almost a dead short and a lot of energy is at the transmitter in commercial antennas which is why you should never EVER touch a live transmitting element as you WILL get burned lol. With an AM/MW antenna the entire pole is live, ShortWave uses very long wires across towers and FM uses lots of types from yagis, log periodic, ground plane X shapes, monopoles, discones, dipole etc.. Basically the higher the frequency, the shorter/smaller the antenna length. Interestingly, behind those small to massive "snare drum shaped" microwave transmitters you see everywhere is just either a small discone, bowtie or dipole element in the center. The drum is just a reflector for line of site comms. :) Probably got some bits wrong but didnt want this to go on forever.. which it has lol
5:20 "The ZTX300 was also one." Instant flash back to Analogue Electronics in Higher Physics, 1986-7, where we had a tray of components and the transistors were ZTX300 and ZTX500.
This is a awesome talk on rf doppler detectors, the bit in the beginning which covers the oscillator and how one can modulate the amplitude is gold. Love it, thanks Clive!
I was on the development team of the C&K/Honeywell DT-7xx k-band Dual Tec microwave/pir motion detectors back in Y2K. I did a lot of GTEM work for rfi and international certifications and UL listing. That round pad pad on the with the positive ring could be adding a few pf capacitance to keep rf noise out of the transistor. RF can be funky at gigahertz frequencies. I watch your videos to jog my memory. My kung fu is old and haven't touched an oscope or frequency analyzer since 2004 working on Pave Paws. That was SLBM rocket science ;)
I have a bunch of these and they are great, but I never bothered to try to figure them out, I didn't do very well in my RF and wireless classes when getting my degree. I understood diversity and multipathing, QAM and PSK, but for actually how circuitry worked and a lot of the math involved, not a chance. That stuff is black magic, to the people that really know it, much respect.
I bought two of these intending to use them as some sort of alarm, (instead of the LED you have) but did not do anything with them. Now I understand what's going on and can proceed further. Thanks a lot for doing this video and also thanks for the many knowledgeable comments from everyone.
I'm using one of those microwave sensors as an under-monitor movement sensor. It is used to switch on an LED strip under my monitor when movement is sensed. The problem I have with these is that the sensing is patchy. They can often see me over the room (and through a wall) but will often not detect when I'm sitting at the keyboard (2ft away) moving my hands about the keyboard and to mouse etc (1ft away). My current solution is to have one under the monitor looking at me and another blu-tac-ed under the wooden desk and mousepad. I've never yet worked out the front/back of the sensor to find the most sensitive side. I've been tempted to try a PIR sensor on the monitor instead but never got around to trying yet.
I bought some of these for a prank on my boss (we are in an office prank war... he started it... lol) and I wanted to know how it worked. Eventually I decided I’ll never know and that all I needed to know is that it did work. Fast forward 2 months and here I am watching Clive on an 8 month old video on the chips I bought. I have been a fan for two years, and somehow this is the one video I missed. Haha, thank you for this closure!
On the note of the "intelligent" powerbanks that shut off... How about a video about modifying them to either not do that or turn down the current they require to be drawn to stay on, if possible? I've had tons of projects where I thought "I could just use a powerbank to power this" and then these "intelligent" ones ruined that idea, especially ones that require something like 200mA minimum to stay on. There's simply no way to use low power stuff like a simple 1 LED light (ikea jansjö USB for example) with long runtime in mind from it because the powerbank will just turn off after 10secs :(
I love these relatively long videos, it's a lazy Saturday afternoon, wife is having a nap with the little one and I can just veg and watch you explain cool stuff. Some of your previous videos have given me great ideas for work projects too (Rpi/arduino stuff), so cheers for that too!
Amazing explanation and homework.. Especially because of the super zoomed PCB picture that was used. I'm sure it helped the viewers understand the PCB a lot more easily. Keep up the good work.
If you ever get interested, I'd love to hear your explanation of mass spectrometers and the quadropole mass selector. They're all about how alternating electric fields interact with ions of different masses.
Clive’s got it right he could be an Electrical Engineer... As my intro to EE professor said the difference between science and engineering is that engineers estimate, like Clive and his capacitor values being feasible, and scientists require exact values meaning they’re not as flexible dealing with real life components’ tolerances.
I think you are correct with the screening you spoke of. Back in my army days that screen was made of copper components and used to tune the device to see it's target.
The mode which always resets before triggering again is useful when you're doing the on/off timing externally. This way the external circuit can continously detect movement.
Microwave RF design is something magic. As I'm not a wizard I don't understand much of it. As a ham radio operator I want to work on the GHz bands as well some time in the future.
Some motion detectors used in security/burglar systems use both a PIR and a microwave detector (called "dual-tech" in North America at least). Both sensors have to detect/trip in order for the zone to be considered violated, which greatly reduces false alarms.
The oscillator circuit is probably common collector. The feedback is from the emitter to the base through a transformer to get the required amplitude increase. Since the collector is grounded, the collector to base capacitance becomes part of the tank circuit and the Miller effect is eliminated. The transistor can then operate at the highest possible frequency.
I once worked in a firm that was involved in microwave sorts of things. You can make a tuned circuit by drilling a hole in a bit of metal and putting a plate on either side. That's your inductor and capacitor right there.... Also wave guides are a lot like plumbing just very precise.
Did anyone else notice how Clive drew his own face in this video? - Just look back at the part where he draws the diagram of the P.I.R. sensor at the top of the sheet.... Now, tell me that's not a self portrait! Thanks, Clive, for another truly enthralling video on something I know absolutely nothing about. - Give me valves (tubes) and high voltages any day. But, we shall learn........
I have some ceiling lamps I bought from Costco that I'm sure have this technology in them. I love when the light goes on when I enter a hallway. For the first 2 months, we all said thank you to the light every time.
My parents bought some cheap PIR ceiling lights recently. I installed on in the laundry. Its quite nice, except for the fact it has no sensitivity adjustment.... And I know I could change the sensitivity by swapping components. But the manufacturer has welded the damn thing shut. The only way to open it is by cutting it.
@@tin2001 The one I got has a remote and I think there's a sensitivity adjustment. Also the color temp, time it stays on, etc... Now if I could only find the remote...
This circuit looks very familiar to the control circuit of a smoke alarm where there is a small amount of a radioactive substance sat in between two conductors, one going to ground or positive and the other to the chip, i think the chip measures the change in voltage in pulses.
Pretty clever. You really gotta stare at it to see all the layers. The single transistor is being used for several things at once. The base is capacitively balanced between the TX and RX in such a way that if they don't cancel each others opposing capacitance charge the difference will change the bias of the transistor. A lot like how a phase lock loop can demodulate FM. It's seems a lot like just a microwave frequency version of a phase lock loop metal detector that's been cleverly manipulated out of a single transistor and some passives. The metal detector doesn't beep unless you swing it, but in this case the coils are stationary and the metal moves. The higher the frequency the more the water in the soil reflects back on a metal detector. That's why they only use around 7khz.
I was trying to figure out how the circiuts work (and they do very well!). Your video was the best and honest video I found! I highly (!) appreciate all the effort and time you have put into making this video, althought english is not my first language and I do not undestand every piece!
Many years ago as i mooched around the local library I noiticed that a book enttled 'The Deadly Fuze' never moved. Eventually curiosity got the better of me and I took it out.Turned out to be the story of the development of the WW2 Proximity Fuze. Built into shells and fired up the barrel of a gun! And this was in the days of valves!! Can't remember the operating frequency but acorn valves could get up to about 500Meg. Used in anti aircraft shells and ordinary artillery shells. And now we've got shells with GPS built in!!!
i just did a thing of which i am inordinately proud. i bought a bunch of these, and decided 3 secs was too brief for the output signal. so i found the data sheet, learned to solder 0603 smd bits, removed the 10nf timing cap, popped a 100nf one in it's stead, and voila! it now switches for 30 seconds...and for my next trick, i just ordered some arduino nano PCBs and all the bits on the BOM. i am only going to try and make my own 'arts and crafts' arduino nano! and a mere year ago i was horrified by the thought of even soldering the headers on one. i learned it all from watching YT vids.
I think the capacitor/trace array is forming something similar to the old ladder line, which is in effect a series of tank circuits. It allows an antenna to be resonant at an improper dimensional characteristic. In effect it's a microwave transmatch to make use of the PCB as combination resonant body and RF emitter. It's been a few years since I was too deep in this stuff, but that's my take (subject to correction) on the oscillator/transmission line/antenna you have there. The presence of the human in the vicinity of the RF field detunes the whole affair, triggering the off delay. It's a lot like a Dip meter. Back in the late 70's this was used for some alarms. Heathkit had one I built for a friend's TV shop, and it had a discrete telephone dialer in it as well, which you set using dip switches. Once triggered, the dialer would use a reed relay to dial your home number (programmed by the switch array), then you would have an open mike in the room so you could listen to the people stealing your stuff.
yet another great vid, always wondered but assumed it was short range radar. the eclipses you talked about, in my experience ... the capacitance is used to tune an antenna wire or in this case the track. for example the 2.4ghrz band ( most wifi traffic and bluetooth ) and the antenna shape and reflectors on the back help with beam forming ( rf shaping or direction ) so... 300 (reference to speed of light acepted figure for antenna calculations) devided by 2400mhz known as 2.4ghz will give you 0.125 of a meter or 12.5cm ( the required antenna electrical length for 2.4ghz) which can be shortened by introducing a week capacitance to allow the physical length of the antenna to be reduced to make it more manageable. most modern antennas are designed this way to reduce physical length without disturbing antenna performance or in some cases actually enhance it. hope im right and this helps.
You're not wrong. Track width and capacitance values of mere picofarads or the reluctance or inductance of micro-henrys, can make a large difference in resonant frequency... Very careful design of layout track width, path and component values are critical... That's why RF equipment has so many variable Caps and tunable coils....or you'd never get an accurate or stable frequency... Tuning RF equipment is an art in itself..... Peace, Keith......
Thanks for this. I bought a dash cam hardwire kit which is apparently a movement detector and it's so light I thought it was fake. All it had was one of these circuit boards. I now see that a tiny circuit is all it takes to make a microwave transmitter!
If you hook up these to a ardunio and solder a wire to the analong input of the chip (I'd have to look which one it is as I don't remember) You can also get reflection intensity on a graph via the serial monitor with a little programming. Put a couple of these on a parabolic dish and you have a low power radar!
I assume the disc and ring are a circular or spherical polarised antenna. The FPV community might say it looks like a linear 5.8Ghz patch antenna with a ring around it. There are many designs of FPV microwave aerials, some appear to short the signal to ground (usually with a twist or three) while others are capacitive - an interesting one which is circular polarised and can be printed cheaply on discs of PCB. It was provided open source by RF legend Maarten Baert. It's currently the most popular design www.maartenbaert.be/quadcopters/antennas/pagoda-antenna/ It would be interesting to grab a load of these detector boards and try overclocking the range using higher voltages, enclosures, Pringles tins etc... Great video as usual Mr Clive!
What is that circuit board that you connected this module to, which also has the leads to the LED coming off of it? A friend of mine is looking for a way to control some kind of valve in their bathroom in a similar way. It should only stay on for 2 seconds if it's triggered, but as far as I know, it does use quite a high current, so there would be the need for a relais?
I've used them as movement sensors in a few motion activated arduino systems. One thing of note (apologies if others have already said this) is they seem to work on detecting motion of fluids (bearing in mind the human body is mostly water). You can prove this by first waving an empty water bottle in front of it, then waving a full water bottle.
That description of how the Doppler detector works at 16:08 was a bit ropy. I think that what actually happens is that the transistor oscillates at a fixed frequency and transmits a GigaHz RF signal. When a moving object reflects some of that signal back then it will be at a slightly different frequency due to the Doppler effect. The antenna receives some of the reflected signal and feeds it back to the transistor. The reflected signal is very small compared to the oscillator voltage and so doesn't affect the oscillation. The nonlinearity of the transistor causes it to act as an RF mixer and generates sum and difference frequencies. The difference frequency is a very low frequency and is passed by the output R-C filter to the BISS001 which thinks it's a signal from a PIR circuit. How the oscillator itself works, Pratchett knows..
This is correct. The circuit acts a simple "Direct Conversion RX". The received Doppler signal is mixed with the original carrier to produce an audio beat note. This audio is filtered and amplified and used to switch the following circuit.
It's still there. Do a search on "People are making a fuss about this being complicated". It might be in a collapsed thread however. You have to open each one.
@@graemezimmer604 Found it - thanks. That was wierd, I found it easily this time by searching on your name but when I did that last time it was nowhere to be seen. It's not nested.
BISS0001 chip is special for PIR controller (Passive Infra-Red), but you can modify this chip into another sensor controller like in this video the chip as a micro-wave proximity sensor.
I think of things like this as engineers taking physics and breaking its back over their knee. In ten years it will probably be taught to 14 year-olds and be considered just normal everyday stuff. I love watching the way technology, behind the scenes, is advancing with quiet, almost, unnoticed, steps. Thank Clive for the excellent video.
I used to make those FM-band transmitters too-- circa 1967. In those days we could buy "Poly-Paks" transistors, basically floor-sweepings. But they were perfectly usable 2N706's, 3 for $1. You could put a crystal microphone onto the base and pick up the signal and sounds for a dozen feet or more. Fun times. It was legal in the USA at power levels up to 50 milliwatts and 3 feet of antenna. You have some base-emitter feedback there.
22:30 the RC circuit (10kOhms + 10nF) has a delay time of "500 us" (2 kilohertz). To get a delay time of 3s the resistor must be 60MOhms instead of 10kOhms - maybe the integrated circuit itself has an input resistance of 60MOhms so that we have a delay time of 3 seconds.
Clive, thank you for teaching me about this device, I've had one in the drawer for quite awhile now. I think i will temper with it's C-TM with resistor and maybe short it out. What i really wanted from this device was the magnitude or perhaps frequency of detection and not so much staying on for a duration.
The ring on the rear is probably acting as a ring resonator at the frequency of interest (perhaps x-band = 10GHz). The ring looks like it’ll couple through the dielectric back to the gate, providing feedback. It’s common in these very low cost microwave circuits to use a single active device as the oscillator, the output amplifier and the receive mixer. Often utilising the parasitic elements within the active devices’ package.
Playing with a circuit like this, LED and sensor, I pounded a large aluminum pie plate into a rough dish reflector. It does seem to add to the range, as I can trip the light at a greater distance with the reflector in place.
I used to make a very similar VHF transmitter circuit, using a varicap diode to alter the frequency for FM modulation. Range about quarter of a mile. I think I used a BC108 transistor. The capacitor across the coil was a variable trimmer type.
Those optional pads on the back - do they essentially provide the functions labelled on a typical generic security light as "running time", "sensitivity" and "daylight cutoff" or similar? You know the ones, standard fit on all such devices, never entirely clear how they work and you just have to fiddle with it semirandomly until it works vaguely like you want it to. So instead of tacking on some additional SM components there'd either be directly mounted variable resistors (and variable capacitor?) with a suitably altered board layout, or flyleads to more flexibly case-mounted ones? Could use similar with this microwave one (probably more the flylead type to prevent interference) and make life easy on yourself / provided extra functionality to the customer, instead of having to work out what value you need to solder in or having it stuck at a single inflexible setting.
The first thing I thought of after seeing this was the infamous AN/TPS-39 intrusion detection system used on Titan II missile sites. They used paired microwave horns creating a perimeter around the silo and were famous for false alarms. Heavy rain, large birds, coyotes, or a bit of snow collecting in the antenna would have security scrambling. I don’t think they ever detected an actual intruder. The technology was not quite as advanced in the early 1960’s when the “Tipsy 39” was designed. What your little circuit board does took a 6’ stack of rack mounted equipment to do.
The guy that "invented" radar, sort of, Watson-Watt got stopped for speeding in the 1960's. His wife told the cop that her husband had invented those. Suspect cop was not impressed.
Fascinating..Ive just bought an outside floodlight with microwave sensor from CPC, havnt put it up yet and wondered how it worked compared to PIR ..Thanks Clive :)
I think the circular track on the back of the board could be the reflector to make the antenna directional. The driven element of the antenna being on the top side of the board.
Regarding power-saving, the microwave circuit need not run continuously but can be powered on briefly to have a "quick look" about once a millisecond. (The commercial unit shown would need modification to achieve this). The homodyne output can then be fed to a sample-and-hold circuit enabled while the microwave power is "on", then amplified conventionally. This is an easy way to reduce power consumption in the microwave part of the circuit by a factor of at least 100. (Probably more than this could be achieved). With a microwave frequency of 3GHz, as suggested, movement with a component of 1m/s (typical of a person) towards or away from the sensor would give an output varying at 2 x 1m/s x 3GHz / c = 20Hz. (The factor of two arises since the moving target reflects the microwaves, compared to the familiar Doppler effect where one end transmits and the other receives). So the receiver should look for signals around that frequency. How low are the frequencies of interest depends on whether or not you want to detect someone creeping about to defeat the system by moving very slowly. The received microwave signal varies in amplitude and phase according to the distances to the (likely numerous) reflecting objects and how reflective they are at microwave frequencies. For the most part, this means that you will detect only movement, as required. But note that movement of the sensor will have the same effect, so you can't use these devices in a pendant lamp if the lamp may swing in the wind. Another problem is that some objects vary their microwave reflectivity even without movement. Modern fluorescent lamps drive their tubes at ultrasonic frequencies (outside the band of interest for our movement detection) but older lamps (with a simple inductive ballast) are driven at the supply frequency so that the density of the contained plasma varies at twice that frequency (100Hz or 120Hz). This may be within our detection band (especially when the microwave frequency is 11GHz or so, which means that the Doppler frequencies are correspondingly higher), and may trigger the detector spuriously. To avoid this, it may help to apply a notch filter at twice the supply frequency. For example, if we sample the environment intermittently (as suggested above) at 1200Hz, it is very cheap (in CPU time) to apply a subtractive comb filter with a delay of 6 samples (if the supply is 50Hz) or 5 samples (if the supply is 60Hz), thereby "notching out" 100Hz or 120Hz as appropriate (and the DC component).
The sensing circuit needs to monitor the ambient level all the time to detect the doppler style interference. It's usually analogue, so can't just sample in bursts like a microcontroller could.
Great to watch you second guess what and how the designer was trying to achieve. There must be a bit of detective Columbo in your DNA. One more thing....
After a not particularly successful foray into FM design (and microstrip technology), I left this area to those who know what they are doing! FAR cheaper to buy pre-aligned FM modules than try to DIY (without the arcane skills this area of electronics seem to require!) :-D
@@stargazer7644 Dead right there mate! When track width / shaping parameters have to be accurate to sub-millimetre levels (and even then there's a lot of adjustment needed for unforeseen / difficult to quantify spurious coupling), witchcraft sums it up VERY accurately!
EXCELLENT Video BigClive, once again you bring us mere mortals outstanding, interesting and simply awe-striking photo overlays with sublime PCB Exploded views, thank you immensely
I looked at the output of this device on a spectrum analyzer and it puts out a very dirty signal centered on 3100 mHz that is about 300 Mhz wide. The frequency spectrum has little peaks on it every 20 mHz or so. If this device wasn't so flea powered, it would be highly illegal. Nevertheless, they are very effective at detecting someone walking by up to 20 feet or more away.
@@NikkiTripPS I believe it's more of a violation of broadcast communications laws. Not dangerous, but more like broadcasting without a license as well as broadcasting over multiple unassigned frequencies. At higher wattage it could potentially interfere with other communications.
I have a 100Wh/87w draw Anker battery, it has a button on it to show the battery health. If I long-hold it it disables the low-current shutdown. idk if others have that though.
A ground plane is equivalent to the missing part of a dipole. It's the reflection which is in the same plane, not the ground-plane itself. That can be at any angle. eg a "ground plane" is at 90 deg. A "droopy ground-plane" is at 45 deg, while a Coaxial dipole is at zero degrees.
at first I thought the circle on the back was a ground but yes I agree BigClive, it's some sort of resonator making virtual capacitors across the base, collector, emitter
11:33 -- The circular ring is connected to a constant voltage (V+), so it's at AC ground. It prevents signals in other parts of the circuit from affecting the voltage of the disc inside the ring. (It's a "guard ring".)
The transistor's collector (C) is connected to this ring / AC ground.
The disc inside the ring is connected to the transistor's base (B).
The S-shaped piece of PCB that's connected to the transistor's emitter (E) is a section of transmission line, which resonates at a particular frequency and which determines the circuit's frequency of oscillation. Since one end of the S-shaped piece of PCB is connected to the transistor's emitter (E), which is the signal source, and since the other end of the S-shaped piece of PCB is connected to capacitors which are connected to ground (so that the far end of the S-shaped strip is at AC ground), then the S-shaped strip is a 1/4 wavelength resonant section of transmission line.
There is feedback between transistor's base (B) and its emitter (E) through the space between the short strip of PCB ("stub") that's connected to B and the section of the S-shaped piece of PCB that's connected to E. The size of the space between that stub and the S-shaped piece of PCB that's connected to E largely determines the degree of coupling (feedback) between the transistor's base and emitter. The longer the space or the narrower the space, the greater the coupling / feedback.
So the circuit is a one transistor oscillator (specifically, a grounded-collector oscillator), having a resonant circuit that's connected to the transistor's emitter, and having some coupling / feedback between its emitter and base.
This guy said PBC multiple times, but assume that he meant PCB, printed circuit board.
Very well said! I have no idea what that really means, but then again, I know virtually nothing about electronics.
@@acmefixer1 -- You're right.
@@therealjamespickering -- The circuit generates microwaves. The microwaves are radiated by the little antenna. When something moves through the field of microwaves, some of the microwaves are the reflected to the antenna, where the reflected signal is absorbed, amplified, and combined with some of the microwaves being generated by the circuit. The result is a small change in the circuit's normal voltages, which the rest of the circuit (the rectangular chip) then detects.
@@kevinbyrne4538 Ok, that's much clearer, thank you! So the S-shaped track oscillates at a frequency of 3.18 GHz and the interaction between this and the disk attached to the base results in a certain voltage to be passed through the emitter? Movement in the room would then result in variations in the voltage?
Does the board only output a high/low digital signal, or is it an analogue signal that could be used to determine something about the size/velocity of the object?
Not an effin clue, but Big Clive's enthusiastic detective work draws you in and you keep watching.
@@N1gel Haha, I don't even know the basics of electronics, but I get drawn into these. I at least have an idea of which components do what, it's just the whys that Confused me, lol.
My list of questions never ends and at some point I will know more, but right now, I still love Clive's vids despite my lack of knowledge...the big surprise I was getting at you know, lol.
@@N1gel Nothing but respect for Clive. Techmoan and Explaining Computers are another couple of very good RUclips channels you might enjoy. :)
@@watsoft70 Glad to know I'm not the only electronics-noob in the audience. Whenever he talks about complicated circuits like this, I'm lucky if I can even follow along half of what's going on.
@@N1gel ... some things are just beyond the ken of mere mortals, and are not meant to be known the wot of. Microwave RF is clearly for wizards and other ethereal beings.
The Concentric Circles thing is the actual Antenna Element Back Plane . The Squiggle Line Track simply a Load Inductor doubling as the Antenna. If you measure the Distance between the Squiggle Track folding back on it's self you will find it a fraction of the actual operating frequency in .wavelength.. Probably 1/8th or 1/4 wavelength.
Agreed, as soon as I saw that I thought linear loading.
The rectangular track on the base pin will probably be 1/4 wave resonant stub too. Don't forget to account for velocity factor when working out the frequency, which is approx 0.5 on FR4.
@@Zadster LOL, That little Stub or Tab is most likely the primary RF Emitting Element. AKa Antenna.
Argh. I should read more before posting. If you think of it as a delay line one end is the frequency of the oscillator right now and the other end is the frequency of the oscillator a few pico seconds ago.
@@pulesjet I'm not so sure, given the electrically "large" area of the disc and the annulus.
Hehe, I also made those “simple” (slightly illegal) FM transmitters when I was young, most often with a preceding microphone amplifier, to become a small bugging device. Often choosing close to 88MHz or 108MHz, and then any ordinary FM-radio (preferably small and hand held) could be used as receivers. I learned then, that there was a big complexity to RF-electronics, since I put a lot of effort in doing very nice and clean builds, with often no good results, while a class mate made a very “ugly” build (blobby soldering, wires not cut close to the PCB etc) and that worked better than any of the rest of the class mates. It’s fantastic that a simple circuit like that actually ends up as a FM-transmitter. The simplicity to build things like this for FM an AM, together with the avast amount of existing equipment, is actually why I feel a bit “scared” that DAB will “destroy” the possibilities for future young kids, interested in electronics, to test and learn in an exiting (slightly illegal) way. Of course you can do a lot of MUCH cooler things today, with all sorts of micro controllers and advanced chips, sensors etc, but not at the same low level.
I’m glad Sweden postponed the switch to DAB. It really feels meaningless, since you could get the digital feeds via mobile data streams and the cost to switch all existing analog equipment would be enormous. It have played out it’s role... Keep at least some of the current FM-band analog (as well as the AM-band) as a backup system and for the kids to play with ;)
Btw, we soldered the antenna (normally measured to a quarter to the wavelength) to one of the loops of the wounded inductor.
My DAB radio failed fairly quickly so I'm still on FM. I wonder if the DAB time signal is still ~4Sec slow????
As 50+ old fart it's been 30 years since I've thought about 1/(2pi*sqrt(LC)). You're video made my brain work - thank you.
If Clive says it's complex it's really complex. Another really interesting video Clive thanks for all the hard work you put into these.
Glad I stumbled on your channel many moons ago, it fascinates me how all these things work and makes me want to get into making a few projects myself
If Clive says it's simple it's complex for me
One of the main textbooks on high speed digital design, not really RF, is literally titled “a handbook of black magic”
Loved this video! The fact that you tried to comprehend the magic of RF and still put out this video - the transparent film screen showing the back was a great way for you to explain of your thought train in a very slick way!. Always look forward to your new content, I’m pretty sure I’ve watched all your back catalogue :-D
A hybrid coupler in ring configuration ("rat race coupler") perhaps. These couplers typically have four ports. Power input at port 1 splits and travels both ways round the ring. At ports 2 and 3 the signal arrives in phase and at port 4 it's out of phase and cancels. The reflected, out of phase signal (from your body) can be made to "unbalance" the ring which effectively brings one port to a higher potential than the other ports. Those eclipsed portions of ring might be the port couplings. Just a guess- I am not a µwave engineer (but have played with transmission lines in the past).
I like it and me too. C band satellite LNB pre amps when 120$ was entry price for a single NEC transistor with a much improved noise figure. Had no real business ordering those and resurrecting dead ones from lightning surges, but I was still more successful than not. Only thing I can recognize here is the quarter wave tank described as the only rectangular item on the board, hanging off the collector. 14:06 Those were very commonly used in that field for side by side coupling of the mixer signals. CRS about too much of it these days, but we are talking mid 80s too. End of the day, way too pricey for me to play and win.
This reminds me of a gadget I built before touch sensors existed. I used a PIC to generate PWM into a coil, which coupled with another coil. Somehow I could measure the phase between coils, which I put through an op-amp and back into the PIC. The theory was that my finger would change the phase. They laughed at me, said it can't work, but it did! I put two of these in a box and by sliding my finger up and down on the surface, I controlled a PWM fluorescent dimmer. Happy memories. My goal was to make a water-proof switch.
Isn't that how metal detectors work?
Nice one, well done.
@@Lasseu basically yes, my first touch sensor I made with a crystal, oscillator a few transistors, resistors, capacitors and a relay.
That's how inventions are made. Though a waterproof switch is much simpler to make, just get a reed switch and a magnet. That's how Nikko did their submarines.
Before touch sensors were around? Seriously? How about 1978 when I made touch sensors using CMOS 4011's? PIC's didn't even exist then. The circuit was simple, touch one spot to turn on and the other spot to turn off. Have to say though, the capacitance coupled sensor would definitely be better and could be made waterproof.
Clive, as a 50+ y/o electronics and radio enthusiast, may I say, if your video's were available when I was doing my training, I would be "up there" now, I really enjoy all your "tear-downs" and the way you detail your explanations. They come across so well. Even something like this complex uWave circuit. Well done.... You're a top bloke!
Sometimes I wonder what effect it would have had on my own learning if RUclips had been around when I was young. It'll be interesting to see how it affects the current generation. They have a lot of technical materials and tools at their disposal.
@@bigclivedotcom Yea, I'm so envious! One of my first "serious" books was a Ladybird book Making a Transistor Radio when I was about 10 - Remember the OC71?
I think this is a voltage controlled oscillator, it doesn’t use a fixed frequency.
As others have said, the circular elements on the back plane are part of the antenna. For this sort of circuit to work the antenna needs to have an outrageously high Q, and ideally a pretty low radiation resistance, which a loop antenna provides. Essentially the ring looks to be a loop antenna acting mostly as a receive antenna. It’s coupled to to the transmit antenna with a sort of hybrid between a gamma match and a Patterson loop style capacitive network.
The 1k resistor and the two adjacent capacitors right before the sense input are an RC pi filter tuned to the oscillator’s stable frequency. When the environment around the sensor changes, the amount of reflected power and the phase of the received signal changes slightly, which causes a change in the circulating current in the receive loop, which causes the complex impedance on the oscillator output to change, which changes the oscillator’s frequency. The frequency change means the signal will move relative to the pass band on the RC pi network, changing the attenuation of the signal and altering the voltage at the sense pin, and the chip just triggers on the change.
If you have an RTL-SDR dongle or similar you should be able to confirm this by watching the signal in the waterfall. I bet it swings like mad when you sweep your hand near the sensor.
Clive, if you don’t have an SDR handy, I’ll order a couple and put it on the spectrum analyzer, and I’ll also send you a little SDR dongle. Super handy little gadgets for poking at RF circuits like this.
Indeed there's a github repo with information about this module (jdesbonnet/RCWL-0516) which mentions: "finally found the signal at 3.181GHz with the HackRF One SDR! One interesting observation: waving my hand in front of the sensor causes significant changes in the transmitting frequency, shifting by up to 1MHz"
Matthijs van Duin that’s interesting, I would actually expect the swing to be much bigger for it to be based on the changing attenuation of the band pass filter. 1MHz swing on a 3GHz signal would probably only be a fraction of a dB even at the steepest part of the filters curve. I wonder if it’s using the op amp that’s on the input of the chip as a phase comparator or something similar.
Hi Bigclive - really interesting video - I remember UHF/Microwave construction being described to me in the late 1970s as a bit like "plumbing" - the usual headache when designing higher and higher frequency circuits was trying to overcome and eliminate stray capacitance, but as you get towards the top end, they stop being a "problem" and start becoming an "enabler" - but you instinctively realise that :)
What's more interesting to see is that (compared to the tolerances within microchip fabrication) the relatively crude technology behind copper etching can be used to great effect.
It's a bit like looking at plans for a fairly crude valve amplifier and realising that the "cleverness" is all down to the physical construction, which we've all kind of forgotten with the ability to cram more and more components into an ever decreasing space to overcome design flaws
This is a perfect example of less being very much more :)
I was a broadcast engineer for a couple of decades, but RF was never my strong suit. I could keep big transmitters running, but I was way more comfortable with studio gear and computer stuff. I totally understand what you're saying!
This will be perfect for catching that ghost that keeps turning on my soldering iron after I turned it off.
id like to hear more about your ghost
I think I may have your same ghost...
Nah, that's just the ghost of Moss.
I bet it's the same ghost that switched my grandmas stove on and ran my water heater for 4 days straight.
If you manage to catch it, make sure it can't hurt anyone again.
@@uzaiyaro So leave the soldering iron OFF, ok Moss? 0188999...
Imagine all the time and research going into the design only to have it copied by the Chinese and sold for 70 cents a module.
It’s amazing how such a simple circuit happens to be so complex. Thanks for breaking it down for us Clive, it’s much appreciated!
Appreciate these videos so much - truly, truly good quality educational content that is often impossible to find. Keep on keepin' on!
The feedback from the collector to the base is in the transistor, mainly the internal capacitance between the collector and emitter. The square trace connected to the base is less an inductor/capacitor and more a delay line. The oscillator operates as a common base amplifier. The "squiggly" emitter line is a delay line. The disk of copper on the bottom behind the transistor is simply a ground plane. Some capacitance is there but it's unintentional. The ring of copper is the actual antenna. The ring and the disk ground plane act like a fresnel lens and makes the radar output more like a dipole antenna. When you move towards or away from the antenna, not only do you cause a doppler shift but you mainly case the frequency to shift (you're now part of the tuned circuit. At cm waves both are pretty much the same thing). The wiggly part of the emitter track introduces a delay from the frequency a few pico seconds ago and mixes it with the frequency that's happening now. In phase oscillations use less current than out of phase oscillations. The increased current drain for an out of phase signal is dropped and filtered by the emitter resistor (which is where the real feedback and transmit occurs) and the associated emitter/ground capacitors for detection.
@@pahom2 Everything is an antenna. In your case the dual squiggly lines is probably being used as an antenna and phase comparator. Remember that at these frequencies there is no real tuning inductor or tuning capacitor. Everything (including you) is part of a tuned circuit.
The ring is a resonator at wavelength equal to its circumference. The top of the ring is pinned firmly to VCC by those bypass capacitors forcing that to be an E field node and the bottom to be an anti-node. The collector and emitter have opposite phase so that the meander line couples to the resonator on the back. Do those two vias on the disk connect to the base? They seem to be about -120/240 degrees away from the top standing wave node. Combined with the transistor characteristics and the base capacitor overlap, I predict this brings the positive feedback into phase with the resonator. Any Doppler effect shift will be f0 (v/c). That disk might couple to reflected energy so that the same transistor mixes those two signals with the 1k -- 1 nF forming the LPF to reject the carrier and sum frequencies.
To paraphrase the late great Arthur C Clarke, microwave technology is indistinguishable from magic.
not sure if it was intended as part of the joke, but arthur c clarke was a radar specialist in WWII so I don't think microwave tech was very magical to him.
This break-down caused me to realize that not every part of a circuit is either positive or negative relative to a connected part; but rather, the relationship can be more complicated; time-based or based on detection/externalities.
Back in electronics school, my teacher had been a elec tech for radios in fighter jets.
He told the story of a jet that would have radio troubles. After some time of trying to figure it out,, the E7 boss man, handed him a can of polish, and told him to polish the inside of the box the radio sat in...
It seems that the box was a capacitor in the circuit. ... hmmm
Well, the polishing worked,,, at least that is what we were told...
Thanks and keep up the good work.
I at one time worked on 45w 850mHz transmitters at the factory. I would tune the circuits be adding or removing silver solder from the copper patterns on the board. They were very sensitive to anything being moved around the power transistors.
850 millihertz transmitters must have needed a very impressive antenna.
@@stargazer7644 Not really. A 850mHz antenna is only about 6 inches long. These were for a early car phone system base station, before cellular phones.
@@oldmgbs2 - Star Gazer is busting your chops a little, for using the 'milli' prefix when you (presumably) intended the 'mega' prefix -- because a sub-1Hz frequency would (of course) need a hella large antenna :-)
@@theskett I didn't even catch that!
"m" for milli (1e-3) or "M" for mega (1e6).
Only accountants use "m" for million. Engineers and scientists use "M".
Just rig a microwave oven to run with the door open, if you smell pork, you have detected a body 😂😂
Oy vey!
*What the hell.. HAHAAAA!!!*
Oh my God man you hate the guy about to break into your house but don't give him cancer!!
Make sure and redesign your room to be the right size resonant cavity faraday cage. Make sure it is grounded. There, now your idea would work, but the sound of people screaming from sudden blindness would be your early warning alarm...
@Dave Micolichek So... it was effective at clearing the morning mind fog?
That RF oscillator could be used as the volume oscillator in a theremin. It would be interesting to attach an oscilloscope to the 'sense' point and see how sensitive it is. I might buy some of these and try to build a theremin.
Im only a low level entry into RF circuits but I am aware in microwave frequencies an antenna called a discone is used most common. They tend to use a capacitive 'hat' and obviously get smaller the higher the frequency, so I think you have a very squashed discone antenna with all the relevant coupling components. The idea with RF is you want as much power thrown out as possible without any RF reflecting back down the feed to the transmitter or damage will occur. I know its very critical with high power outputs, but not so sure with very low power like this but it could have an effect if not controlled properly. It is called a discone because that is exactly what it looks like, a disc on a cone with an insulated separator between them. The disc is fed with RF and the cone is the ground reference and the size and angle relationship ( radius of disc and angle/length of cone with solid cone and disc or using rods as a cone and disc ) between them determines the frequency you want to transmit at. As mentioned by another commenter further down the receive parameters of the antenna will usually be compromised by a fraction of the desired transmit frequency ie 1/2 wave, 1/4, 1/8, 3/8 etc are typical because of size limitations on the board or your available space at home because the actual size required for a 1:1 transmitter in most cases would be far greater than the space available. Reception through an antenna does not need to bother so much with sizes of things as all it does is alter the amount of energy/noise/interference available to be received. In short, the antenna length/size must be a fraction of the wavelength of the frequency you wish to transmit at and the load on the transmitter device should be as close to 50 ohms as possible to prevent a dead short, because transmitting RF is almost a dead short and a lot of energy is at the transmitter in commercial antennas which is why you should never EVER touch a live transmitting element as you WILL get burned lol. With an AM/MW antenna the entire pole is live, ShortWave uses very long wires across towers and FM uses lots of types from yagis, log periodic, ground plane X shapes, monopoles, discones, dipole etc.. Basically the higher the frequency, the shorter/smaller the antenna length. Interestingly, behind those small to massive "snare drum shaped" microwave transmitters you see everywhere is just either a small discone, bowtie or dipole element in the center. The drum is just a reflector for line of site comms. :) Probably got some bits wrong but didnt want this to go on forever.. which it has lol
5:20 "The ZTX300 was also one." Instant flash back to Analogue Electronics in Higher Physics, 1986-7, where we had a tray of components and the transistors were ZTX300 and ZTX500.
Where is the Signal Path god when you need him...
This is a awesome talk on rf doppler detectors, the bit in the beginning which covers the oscillator and how one can modulate the amplitude is gold.
Love it, thanks Clive!
I was on the development team of the C&K/Honeywell DT-7xx k-band Dual Tec microwave/pir motion detectors back in Y2K. I did a lot of GTEM work for rfi and international certifications and UL listing. That round pad pad on the with the positive ring could be adding a few pf capacitance to keep rf noise out of the transistor. RF can be funky at gigahertz frequencies. I watch your videos to jog my memory. My kung fu is old and haven't touched an oscope or frequency analyzer since 2004 working on Pave Paws. That was SLBM rocket science ;)
I'm grateful that they broke out the 3.3v supply as well - used this in a project recently. Had no idea that the RF part was basically black magic.
I have a bunch of these and they are great, but I never bothered to try to figure them out, I didn't do very well in my RF and wireless classes when getting my degree. I understood diversity and multipathing, QAM and PSK, but for actually how circuitry worked and a lot of the math involved, not a chance. That stuff is black magic, to the people that really know it, much respect.
I bought two of these intending to use them as some sort of alarm, (instead of the LED you have) but did not do anything with them. Now I understand what's going on and can proceed further. Thanks a lot for doing this video and also thanks for the many knowledgeable comments from everyone.
I'm using one of those microwave sensors as an under-monitor movement sensor. It is used to switch on an LED strip under my monitor when movement is sensed. The problem I have with these is that the sensing is patchy. They can often see me over the room (and through a wall) but will often not detect when I'm sitting at the keyboard (2ft away) moving my hands about the keyboard and to mouse etc (1ft away). My current solution is to have one under the monitor looking at me and another blu-tac-ed under the wooden desk and mousepad.
I've never yet worked out the front/back of the sensor to find the most sensitive side. I've been tempted to try a PIR sensor on the monitor instead but never got around to trying yet.
It may help to extend the run time so that the occasional detection restarts the timer. I use an outdoor PIR unit on my bench lights.
I bought some of these for a prank on my boss (we are in an office prank war... he started it... lol) and I wanted to know how it worked. Eventually I decided I’ll never know and that all I needed to know is that it did work. Fast forward 2 months and here I am watching Clive on an 8 month old video on the chips I bought. I have been a fan for two years, and somehow this is the one video I missed. Haha, thank you for this closure!
On the note of the "intelligent" powerbanks that shut off... How about a video about modifying them to either not do that or turn down the current they require to be drawn to stay on, if possible? I've had tons of projects where I thought "I could just use a powerbank to power this" and then these "intelligent" ones ruined that idea, especially ones that require something like 200mA minimum to stay on. There's simply no way to use low power stuff like a simple 1 LED light (ikea jansjö USB for example) with long runtime in mind from it because the powerbank will just turn off after 10secs :(
IIRC, you can change the value of one of the capacitors to prevent that behaviour.
Check out Mr Carlson's Lab RUclips channel.
I love these relatively long videos, it's a lazy Saturday afternoon, wife is having a nap with the little one and I can just veg and watch you explain cool stuff.
Some of your previous videos have given me great ideas for work projects too (Rpi/arduino stuff), so cheers for that too!
"veg"? Can I ask what "vegging" is?/
It may actually be more interesting watching Clive when he doesn't know exactly what's going on than when he does.
Preach :-D
Perfect timing, I just took delivery of 10 of these microwave detectors and haven't opened them yet! Cheers
Amazing explanation and homework.. Especially because of the super zoomed PCB picture that was used. I'm sure it helped the viewers understand the PCB a lot more easily. Keep up the good work.
If you ever get interested, I'd love to hear your explanation of mass spectrometers and the quadropole mass selector. They're all about how alternating electric fields interact with ions of different masses.
Clive’s got it right he could be an Electrical Engineer...
As my intro to EE professor said the difference between science and engineering is that engineers estimate, like Clive and his capacitor values being feasible, and scientists require exact values meaning they’re not as flexible dealing with real life components’ tolerances.
This also explains why most engineers are INTJ (me included) on the personality testing scale.
I think you are correct with the screening you spoke of. Back in my army days that screen was made of copper components and used to tune the device to see it's target.
You’re just an incredibly brilliant dude.
Old videos and new, I’m always blown away.
The mode which always resets before triggering again is useful when you're doing the on/off timing externally. This way the external circuit can continously detect movement.
Or if you want to scare deer in your back yard by flashing lights at them in odd intervals.
Clive I think this was the best one yet.
The big track on the base is coupling to the tuned circuit on the emitter. That is positive feedback so it oscillates.
Microwave RF design is something magic. As I'm not a wizard I don't understand much of it. As a ham radio operator I want to work on the GHz bands as well some time in the future.
The magic fades pretty quick once you start mucking around with it. Go on AliExpress, lots of little SMA-equipped modules to play with.
Some motion detectors used in security/burglar systems use both a PIR and a microwave detector (called "dual-tech" in North America at least). Both sensors have to detect/trip in order for the zone to be considered violated, which greatly reduces false alarms.
The oscillator circuit is probably common collector. The feedback is from the emitter to the base through a transformer to get the required amplitude increase. Since the collector is grounded, the collector to base capacitance becomes part of the tank circuit and the Miller effect is eliminated. The transistor can then operate at the highest possible frequency.
I once worked in a firm that was involved in microwave sorts of things. You can make a tuned circuit by drilling a hole in a bit of metal and putting a plate on either side. That's your inductor and capacitor right there.... Also wave guides are a lot like plumbing just very precise.
Did anyone else notice how Clive drew his own face in this video? - Just look back at the part where he draws the diagram of the P.I.R. sensor at the top of the sheet.... Now, tell me that's not a self portrait!
Thanks, Clive, for another truly enthralling video on something I know absolutely nothing about. - Give me valves (tubes) and high voltages any day. But, we shall learn........
I have some ceiling lamps I bought from Costco that I'm sure have this technology in them. I love when the light goes on when I enter a hallway. For the first 2 months, we all said thank you to the light every time.
My parents bought some cheap PIR ceiling lights recently. I installed on in the laundry. Its quite nice, except for the fact it has no sensitivity adjustment.... And I know I could change the sensitivity by swapping components. But the manufacturer has welded the damn thing shut. The only way to open it is by cutting it.
@@tin2001 The one I got has a remote and I think there's a sensitivity adjustment. Also the color temp, time it stays on, etc... Now if I could only find the remote...
This circuit looks very familiar to the control circuit of a smoke alarm where there is a small amount of a radioactive substance sat in between two conductors, one going to ground or positive and the other to the chip, i think the chip measures the change in voltage in pulses.
Pretty clever. You really gotta stare at it to see all the layers. The single transistor is being used for several things at once. The base is capacitively balanced between the TX and RX in such a way that if they don't cancel each others opposing capacitance charge the difference will change the bias of the transistor. A lot like how a phase lock loop can demodulate FM. It's seems a lot like just a microwave frequency version of a phase lock loop metal detector that's been cleverly manipulated out of a single transistor and some passives. The metal detector doesn't beep unless you swing it, but in this case the coils are stationary and the metal moves. The higher the frequency the more the water in the soil reflects back on a metal detector. That's why they only use around 7khz.
I was trying to figure out how the circiuts work (and they do very well!). Your video was the best and honest video I found! I highly (!) appreciate all the effort and time you have put into making this video, althought english is not my first language and I do not undestand every piece!
your large format pcbs are a brilliant display tool. What an excellent presentation.
Great work Clive..these videos generate thought, conversation and new ideas..keep them coming.
Gary in USA
Many years ago as i mooched around the local library I noiticed that a book enttled 'The Deadly Fuze' never moved. Eventually curiosity got the better of me and I took it out.Turned out to be the story of the development of the WW2 Proximity Fuze. Built into shells and fired up the barrel of a gun! And this was in the days of valves!! Can't remember the operating frequency but acorn valves could get up to about 500Meg. Used in anti aircraft shells and ordinary artillery shells.
And now we've got shells with GPS built in!!!
i just did a thing of which i am inordinately proud. i bought a bunch of these, and decided 3 secs was too brief for the output signal. so i found the data sheet, learned to solder 0603 smd bits, removed the 10nf timing cap, popped a 100nf one in it's stead, and voila! it now switches for 30 seconds...and for my next trick, i just ordered some arduino nano PCBs and all the bits on the BOM. i am only going to try and make my own 'arts and crafts' arduino nano! and a mere year ago i was horrified by the thought of even soldering the headers on one. i learned it all from watching YT vids.
A collaboration with the Signal Path is called for.
I think the capacitor/trace array is forming something similar to the old ladder line, which is in effect a series of tank circuits. It allows an antenna to be resonant at an improper dimensional characteristic. In effect it's a microwave transmatch to make use of the PCB as combination resonant body and RF emitter. It's been a few years since I was too deep in this stuff, but that's my take (subject to correction) on the oscillator/transmission line/antenna you have there.
The presence of the human in the vicinity of the RF field detunes the whole affair, triggering the off delay. It's a lot like a Dip meter.
Back in the late 70's this was used for some alarms. Heathkit had one I built for a friend's TV shop, and it had a discrete telephone dialer in it as well, which you set using dip switches. Once triggered, the dialer would use a reed relay to dial your home number (programmed by the switch array), then you would have an open mike in the room so you could listen to the people stealing your stuff.
No, just no.
yet another great vid, always wondered but assumed it was short range radar. the eclipses you talked about, in my experience ... the capacitance is used to tune an antenna wire or in this case the track. for example the 2.4ghrz band ( most wifi traffic and bluetooth ) and the antenna shape and reflectors on the back help with beam forming ( rf shaping or direction ) so... 300 (reference to speed of light acepted figure for antenna calculations) devided by 2400mhz known as 2.4ghz will give you 0.125 of a meter or 12.5cm ( the required antenna electrical length for 2.4ghz) which can be shortened by introducing a week capacitance to allow the physical length of the antenna to be reduced to make it more manageable. most modern antennas are designed this way to reduce physical length without disturbing antenna performance or in some cases actually enhance it. hope im right and this helps.
You're not wrong. Track width and capacitance values of mere picofarads or the reluctance or inductance of micro-henrys, can make a large difference in resonant frequency... Very careful design of layout track width, path and component values are critical... That's why RF equipment has so many variable Caps and tunable coils....or you'd never get an accurate or stable frequency... Tuning RF equipment is an art in itself.....
Peace, Keith......
Thanks for this. I bought a dash cam hardwire kit which is apparently a movement detector and it's so light I thought it was fake. All it had was one of these circuit boards. I now see that a tiny circuit is all it takes to make a microwave transmitter!
That blue battery usb suply make me think of another divice :-), Thumps upp as always.
What device..
Heh
Thumbs up where?
at 0.49 , he's also talking about bigger ones .....
Yes it does remind me a little of the "Should I stik this up my ass" video released some time ago.
If you hook up these to a ardunio and solder a wire to the analong input of the chip (I'd have to look which one it is as I don't remember) You can also get reflection intensity on a graph via the serial monitor with a little programming. Put a couple of these on a parabolic dish and you have a low power radar!
could this help to isolate false positives from plants/leaf movement?
Thanks for doing the hard work. I ordered a bunch of these several months ago and plugged one in. It works! I just never got around to a tear-down.
I assume the disc and ring are a circular or spherical polarised antenna. The FPV community might say it looks like a linear 5.8Ghz patch antenna with a ring around it. There are many designs of FPV microwave aerials, some appear to short the signal to ground (usually with a twist or three) while others are capacitive - an interesting one which is circular polarised and can be printed cheaply on discs of PCB. It was provided open source by RF legend Maarten Baert. It's currently the most popular design www.maartenbaert.be/quadcopters/antennas/pagoda-antenna/
It would be interesting to grab a load of these detector boards and try overclocking the range using higher voltages, enclosures, Pringles tins etc... Great video as usual Mr Clive!
Just mount one at the focus of your satellite antenna.
No. A simple ring does not give circular polarization.
@@graemezimmer604 You're right. It's probably more like this design www.maartenbaert.be/quadcopters/antennas/triple-feed-patch-antenna/
What is that circuit board that you connected this module to, which also has the leads to the LED coming off of it? A friend of mine is looking for a way to control some kind of valve in their bathroom in a similar way. It should only stay on for 2 seconds if it's triggered, but as far as I know, it does use quite a high current, so there would be the need for a relais?
You can get water valve control units with hand-sensing taps (reflected infrared) on eBay. They run from batteries.
I've used them as movement sensors in a few motion activated arduino systems. One thing of note (apologies if others have already said this) is they seem to work on detecting motion of fluids (bearing in mind the human body is mostly water). You can prove this by first waving an empty water bottle in front of it, then waving a full water bottle.
That description of how the Doppler detector works at 16:08 was a bit ropy. I think that what actually happens is that the transistor oscillates at a fixed frequency and transmits a GigaHz RF signal. When a moving object reflects some of that signal back then it will be at a slightly different frequency due to the Doppler effect. The antenna receives some of the reflected signal and feeds it back to the transistor. The reflected signal is very small compared to the oscillator voltage and so doesn't affect the oscillation. The nonlinearity of the transistor causes it to act as an RF mixer and generates sum and difference frequencies. The difference frequency is a very low frequency and is passed by the output R-C filter to the BISS001 which thinks it's a signal from a PIR circuit. How the oscillator itself works, Pratchett knows..
This is correct. The circuit acts a simple "Direct Conversion RX". The received Doppler signal is mixed with the original carrier to produce an audio beat note. This audio is filtered and amplified and used to switch the following circuit.
and the Oscillator is dead simple (I've described it above).
@@graemezimmer604 _ I can't find your explanation of how the oscillator works, have you deleted it?
It's still there. Do a search on "People are making a fuss about this being complicated".
It might be in a collapsed thread however. You have to open each one.
@@graemezimmer604 Found it - thanks. That was wierd, I found it easily this time by searching on your name but when I did that last time it was nowhere to be seen. It's not nested.
Great work Clive. Embedding these in a timber staircase to identify individual steps. Then to trigger LED lighting.
Something to consider might be piezoelectric disks to detect physical step contact from underneath.
that usb power bank is "DIRTY", cant even imagine what i thought it was when i first saw it.
hahahaaaa
BISS0001 chip is special for PIR controller (Passive Infra-Red), but you can modify this chip into another sensor controller like in this video the chip as a micro-wave proximity sensor.
The frequency is this module uses is about 2,9 - 3,2 GHz. There seems to be no modulation of the carrier
I think of things like this as engineers taking physics and breaking its back over their knee. In ten years it will probably be taught to 14 year-olds and be considered just normal everyday stuff. I love watching the way technology, behind the scenes, is advancing with quiet, almost, unnoticed, steps.
Thank Clive for the excellent video.
I used to make those FM-band transmitters too-- circa 1967.
In those days we could buy "Poly-Paks" transistors, basically floor-sweepings. But they were perfectly usable 2N706's, 3 for $1.
You could put a crystal microphone onto the base and pick up the signal and sounds for a dozen feet or more. Fun times. It was legal in the USA at power levels up to 50 milliwatts and 3 feet of antenna.
You have some base-emitter feedback there.
22:30 the RC circuit (10kOhms + 10nF) has a delay time of "500 us" (2 kilohertz). To get a delay time of 3s the resistor must be 60MOhms instead of 10kOhms - maybe the integrated circuit itself has an input resistance of 60MOhms so that we have a delay time of 3 seconds.
Clive, thank you for teaching me about this device, I've had one in the drawer for quite awhile now. I think i will temper with it's C-TM with resistor and maybe short it out. What i really wanted from this device was the magnitude or perhaps frequency of detection and not so much staying on for a duration.
That may switch it on permanently. Adding a resistor reduces the resistance as it will be in parallel with that inside the chip.
The ring on the rear is probably acting as a ring resonator at the frequency of interest (perhaps x-band = 10GHz). The ring looks like it’ll couple through the dielectric back to the gate, providing feedback.
It’s common in these very low cost microwave circuits to use a single active device as the oscillator, the output amplifier and the receive mixer. Often utilising the parasitic elements within the active devices’ package.
Playing with a circuit like this, LED and sensor, I pounded a large aluminum pie plate into a rough dish reflector. It does seem to add to the range, as I can trip the light at a greater distance with the reflector in place.
I used to make a very similar VHF transmitter circuit, using a varicap diode to alter the frequency for FM modulation. Range about quarter of a mile. I think I used a BC108 transistor. The capacitor across the coil was a variable trimmer type.
Those optional pads on the back - do they essentially provide the functions labelled on a typical generic security light as "running time", "sensitivity" and "daylight cutoff" or similar? You know the ones, standard fit on all such devices, never entirely clear how they work and you just have to fiddle with it semirandomly until it works vaguely like you want it to.
So instead of tacking on some additional SM components there'd either be directly mounted variable resistors (and variable capacitor?) with a suitably altered board layout, or flyleads to more flexibly case-mounted ones? Could use similar with this microwave one (probably more the flylead type to prevent interference) and make life easy on yourself / provided extra functionality to the customer, instead of having to work out what value you need to solder in or having it stuck at a single inflexible setting.
I was impressed I have ordered 10 from Ali, @31 pence each, it's crazy that you can buy something so clever for so little.
The first thing I thought of after seeing this was the infamous AN/TPS-39 intrusion detection system used on Titan II missile sites. They used paired microwave horns creating a perimeter around the silo and were famous for false alarms. Heavy rain, large birds, coyotes, or a bit of snow collecting in the antenna would have security scrambling. I don’t think they ever detected an actual intruder. The technology was not quite as advanced in the early 1960’s when the “Tipsy 39” was designed. What your little circuit board does took a 6’ stack of rack mounted equipment to do.
The guy that "invented" radar, sort of, Watson-Watt got stopped for speeding in the 1960's. His wife told the cop that her husband had invented those. Suspect cop was not impressed.
I made these when I was kid too. I can remember my mother nearly feel off her chair when she heard me on the radio
Fascinating..Ive just bought an outside floodlight with microwave sensor from CPC, havnt put it up yet and wondered how it worked compared to PIR ..Thanks Clive :)
I think the circular track on the back of the board could be the reflector to make the antenna directional. The driven element of the antenna being on the top side of the board.
its the RF "skin effect" that makes this so mystical
Regarding power-saving, the microwave circuit need not run continuously but can be powered on briefly to have a "quick look" about once a millisecond. (The commercial unit shown would need modification to achieve this). The homodyne output can then be fed to a sample-and-hold circuit enabled while the microwave power is "on", then amplified conventionally. This is an easy way to reduce power consumption in the microwave part of the circuit by a factor of at least 100. (Probably more than this could be achieved).
With a microwave frequency of 3GHz, as suggested, movement with a component of 1m/s (typical of a person) towards or away from the sensor would give an output varying at 2 x 1m/s x 3GHz / c = 20Hz. (The factor of two arises since the moving target reflects the microwaves, compared to the familiar Doppler effect where one end transmits and the other receives). So the receiver should look for signals around that frequency. How low are the frequencies of interest depends on whether or not you want to detect someone creeping about to defeat the system by moving very slowly.
The received microwave signal varies in amplitude and phase according to the distances to the (likely numerous) reflecting objects and how reflective they are at microwave frequencies. For the most part, this means that you will detect only movement, as required. But note that movement of the sensor will have the same effect, so you can't use these devices in a pendant lamp if the lamp may swing in the wind.
Another problem is that some objects vary their microwave reflectivity even without movement. Modern fluorescent lamps drive their tubes at ultrasonic frequencies (outside the band of interest for our movement detection) but older lamps (with a simple inductive ballast) are driven at the supply frequency so that the density of the contained plasma varies at twice that frequency (100Hz or 120Hz). This may be within our detection band (especially when the microwave frequency is 11GHz or so, which means that the Doppler frequencies are correspondingly higher), and may trigger the detector spuriously. To avoid this, it may help to apply a notch filter at twice the supply frequency. For example, if we sample the environment intermittently (as suggested above) at 1200Hz, it is very cheap (in CPU time) to apply a subtractive comb filter with a delay of 6 samples (if the supply is 50Hz) or 5 samples (if the supply is 60Hz), thereby "notching out" 100Hz or 120Hz as appropriate (and the DC component).
The sensing circuit needs to monitor the ambient level all the time to detect the doppler style interference. It's usually analogue, so can't just sample in bursts like a microcontroller could.
Great to watch you second guess what and how the designer was trying to achieve. There must be a bit of detective Columbo in your DNA. One more thing....
After a not particularly successful foray into FM design (and microstrip technology), I left this area to those who know what they are doing! FAR cheaper to buy pre-aligned FM modules than try to DIY (without the arcane skills this area of electronics seem to require!) :-D
FM modules are DC compared to microwave witchcraft. :)
@@stargazer7644 Dead right there mate! When track width / shaping parameters have to be accurate to sub-millimetre levels (and even then there's a lot of adjustment needed for unforeseen / difficult to quantify spurious coupling), witchcraft sums it up VERY accurately!
I feel like I should be getting course credit for this. Very nice video!
if you pass the quiz...
EXCELLENT Video BigClive, once again you bring us mere mortals outstanding, interesting and simply awe-striking photo overlays with sublime PCB Exploded views, thank you immensely
I looked at the output of this device on a spectrum analyzer and it puts out a very dirty signal centered on 3100 mHz that is about 300 Mhz wide. The frequency spectrum has little peaks on it every 20 mHz or so. If this device wasn't so flea powered, it would be highly illegal. Nevertheless, they are very effective at detecting someone walking by up to 20 feet or more away.
Just curious, What exactly is the issue with it that makes it illegal? is it dangerous or just a powerful transmitter?
@@NikkiTripPS I believe it's more of a violation of broadcast communications laws. Not dangerous, but more like broadcasting without a license as well as broadcasting over multiple unassigned frequencies. At higher wattage it could potentially interfere with other communications.
These will also work when fitted directly inside the plastic lid of an IP65 junction box/enclosure (as long as the plastic isn't too thick).
I have a 100Wh/87w draw Anker battery, it has a button on it to show the battery health. If I long-hold it it disables the low-current shutdown. idk if others have that though.
A ground plane at RF is not screening, it's a mirror that doubles the length of the aerial.
Not when it is in the same plane as the antenna.
A ground plane is equivalent to the missing part of a dipole. It's the reflection which is in the same plane, not the ground-plane itself. That can be at any angle. eg a "ground plane" is at 90 deg. A "droopy ground-plane" is at 45 deg, while a Coaxial dipole is at zero degrees.
Except this is an end-fed half-wave dipole. The Transistor is driving the end (about 5K impedance) against the ground at the other end.
Clive, you should get your amateur radio license! So much RUclips potential!
at first I thought the circle on the back was a ground but yes I agree BigClive, it's some sort of resonator making virtual capacitors across the base, collector, emitter