#7: Monitor your Ham Radio transmitter with an oscilloscope
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- Опубликовано: 29 июн 2024
- This video shows a few ways that you can monitor your ham radio transmitter with an oscilloscope. Look at the RF carrier, the carrier envelope, the amplitude demodulated signal, as well as linearity "trapazoid" patterns (please see below). It shows a simple circuit I put together for a local ham radio club meeting and presentation.
I put this circuit together to show the radio club members examples of a sampler and a amplitude demodulator. Of course, since these were built onto the same "demonstrator" board with a common RF input, the linearity can not be measured with this since any non-linearity in the output would appear in both sensors. This is indicated by the notes in the video. In order to truly measure the non-linearity of an amplifier or a modulator/exciter, the X-input would normally be driven by the baseband signal, or the demodulated input to an amplifier, etc., and the RF output would be sensed with the sampler and applied to the Y input of the scope. 
Наука
Nice video OM! Right to the point, no fluff. A+
Alan, had to check out your video and build this circuit as I have built another AM station. Using a James Millen 80991 (push pull 812A, swinging link coupled) and modulating it with a pair of 4-125A and a BC-610 modulation transformer mostly on 40M but sometimes on 20M. Don't have enough room for an 80M antenna. I have two 485 and they are still magnificent scopes even 10 years after you posted this video. I guess they are getting to be around 50 years old. 73
Alan
First of all, thank you for your excellent videos. You are to be commended for sharing your knowledge and expertise on the most important of all test equipment,
The Scope!
I finally got around to building this. Cost about 10 dollars and about 30 minutes to assemble. A very easy project to reproduce. I built mine in a small BUD enclosure.
Using a spare 40 mhz scope that was given to me (leaving my Tek 475 in my shop) I hooked it up to the RF output of the shack switching circuit so I can monitor all of my rigs, I have several.
Using my BC-610-E transmitter, I monitored my carrier and modulation with ease.
It makes a huge difference in determining the health of my signal. Even an inexpensive dual trace scope is a much needed tool, a must for the serious minded operator intent on controlling the quality of the signal.
Remember folks, the scope never lies. If you want the truth about your station, the scope will tell you more at a glance than most any other piece of gear.
Thanks again Alan.
73 de Billy N6YW
I was just searching for a practice demonstration about this stuff. Thank you so much for sharing this simple circuit that is a useful tool for practical analysis. I will better use my scope now. Thanks a lot !
Cool video. Great explanation on using the O'scope. Nice detector circuit.
Thanks for taking time in the making of this video.
73.
Thanks for sharing this. I haven't seen a trapezoid display in years.
Yet another video, exactly what I was looking for, tyvm for posting. Please consider posting a video showing your ham shack sometime, I would love to see your rigs.
Very interesting video, I have never seen the trapazoid pattern on the X-Y mode, very useful indeed! Thanks for sharing.
Thank you so much for this video-just getting back into radio after a few years, and always wondered what the oscilloscopes were used for in other ham's setups. 73
Very excellent presentation, thanks W4RFM Bob
Nice demo. Thanks for taking the time to put it together.
-uploadJ
.
Great video. One of the most helpfull & useful I have found on RUclips for Ham Radio.
73's DE K3ZW
You really are a great teacher!
Just what I was looking for! Thanks again.
What a superb scope display!! BRILLIANT.even though i dont understand everything you are saying, no one could explain it better_!
Excellent video, thanks and this is just the circuit I am looking for since I want to use my scope for just this purpose on the test bench here now..
Very nice. Thanks for sharing that circuit with us. I will build one. 73's W5ZX.
Yes, it does help and Thank You. I'm in the process of buying an oscilloscope right now, first one. I'm going to do a bit of experimenting and all this info is very helpful!
Kevin
N2FLP
Great video as always, I was setting up to do similar but my ancient oscilloscope had not been powered up for ages, it ran for perhaps a minute before a loud bang and a shack full of smoke! An easy repair but kind of comical how a simple task can get sidetracked!
He ran through this in a few minutes. But it will take me over an hour to do the same thing. That’s ok, still beats working in the yard.
Thanks for the video!
Hey Alan, I just completed this little project only I used the SO-239 UHF connectors. I purchased a ABS plastic project enclosure box from Radio Shack. In order to connect to the scope I used 2 uhf to bnc adapters, and then my regular RG-58 patch cables from the radio RF IN, & RF OUT to the dummy load. I tuned my transceiver to 7.100 CW but couldn't get a wave form probably due to the scope not being ajusted. Found SSB worked great & my wife was amazed at her voice print on the scope. 73's
Very, very good video. Thanks !
As a note to people looking to understand this fascinating stuff, last spring I took Electronics 101 at the good old City College of San Francisco. Last month I finished Electronics 102 (transformers/diodes/rectifiers/transistors). But I could figure out your circuit diagram! Gotta love diodes.
Fantastic, thanks for posting.
Thanks for posting this vid! It sure beats a "magic" tee!
I enjoyed your video !! Gary Grove
Thanks for making this video! I'm studying electrical engineering right now, and most of my time goes into learning the theory, but this video shows how Ham is very relevant to gaining some hands on experience.
Ham radio is one great way to get involved in hands on electronics, since we are permitted to design, build and use our own gear.
w2aew I am planning to start with the pine board project by Bob Heil. Do you have any suggestions for other designs or projects that would be good to start with?
I probably wouldn't start with that as your first project, mainly because it uses line/high voltage and vacuum tubes. Plus, the end goal is a transmitter, which would can't use until you're licensed. I'd probably start by building a HF or shortwave receiver - tons of plans online.
w2aew Thanks! I'll search for some plans.
I gotta say I like the look and feel of old oscilloscopes like the Tektronix 485
Excellent!! One thing that would be nice, in the future, if possible, would be to see examples of non-linearity, flat topping, and various examples of problems with the TX of SSB, AM, and other modes in a transceiver.
Very nice. I've been scouring the web for a circuit like this, CleanRF makes something similar, the RF-SM which is a little pricy for my tastes. Even a search of the ARRL archives didn't reveal any home brew circuits. With radios like the FT-857D that have multiple controls for the microphone audio, i.e. compression level, mic gain, DSP mic equalizer, being able to monitor the SSB RF envelope becomes important in order to properly set the levels. Add in an amplified mic, even more so.
First of all, I thank God for your life and for your excellent videos. You are to be
commended for sharing your knowledge. i am beginner in this field so i look to you.
stay bless
I inherited an oscilloscope, now I can try it out!
great video, thanks for sharing
Sorry, i just forgot to see the final part, good work!!!
This is a great video. I tried this technique to analyze the output of my airband transceiver on a PM3092 Oscilloscope (sniffing the output between the rig and a dummy load), but the computer inside the scope went a bit mental. I am now looking for a Tek scope !
Philips PM3092 oscilloscope goes crazy with 127MHz input
Alan, thank you for your time creating this fine video. I read through a lot of the replys but did not see anyone ask what is this max wattage this guy will handle ,by the size of the components not much I assume. Thank you Joel
john, great explanation you are a genius mate could you possibly do a video on how a car key fob works how to program etc .
please keep the vids coming, john
+Joseph Duane Yuna. Is this archaic and unnecessary? Sure it is. But, that's not the point of it. It is interesting, fun, entertaining and educational.
I would go further. Many people enjoy using vintage transmitters and for them, these methods are valuable. Furthermore, there is real value (point if you will) in having fun.
It's not at all archaic and unnecessary. I am a general class ham and recently added a cheap AM CB to my station. There are some local hams who like to chat on 11 meters. I plan on getting an SSB CB. Many CBer's like to "peak and tune" their radios. If I get something used there is a chance that it's been messed with. A watt meter will make sure it's within FCC specs for power output. With your circuit I can use my O-scope to make sure the radio isn't over modulating. So there are perfectly good reasons to do what you show in the video.
Thanks for posting this!
purplemutantas Unnecessary and archaic? Not on your worst day ( or any one else' s either) This circuit, as well as the one I have designed on my own is and has been indispensable for the past 35 years to me. W ether used for CB, HAM, HT's and Linear Amps or QR P, it's the way to tune your transmitter in conjunction with an AF signal generator, RF generator, PEAK reading and RMS watt meter, frequency counter and ammeter. How can any shop or shack get it truly "right", without tuning on a scope ? Many shops don't care as long as the radio is on freq. and sounds alright. Then of course, we may or may not have a spectrum analyzer to really see whats happening after the fact! As I'm sure you also know "seeing" your RF output in conjunction with a freq. counter will allow you to check that your carrier oscillators in ANY SSB/ AM transmitter SUCH AS A CB even for example- is not only on frequency, but what your RF output looks like on a scope as a result of those carrier oscillators and if they are sensitive to a physical shock or vibration in the mobile. also at various power output levels too. Not to mention A TWO TONE Generator. If you know what you're doing, then you know what I'm saying/ This is absolutely necessary for any tech who wants it all to work properly, sound properly, and of course- on frequency. This simple circuit is indispensable and I made one the way I wanted for my own reasons.The first one I designed --would show a perfect image into a scope with a 1 MHz. maximum vertical bandwidth amp; into an old tube type Eico scope I got for $10. I just had to let you guys know about this after some opinions I had read here.
+purplemutantas You worry too much about staying within power limits on CB. I am a ham but use CB for traffic info when traveling. Just about any day I can hear stations on channel 6 that are obviously running multi kw output, over modulating and splattering over many channels. This has been ongoing for years and so far, the FCC apparently hasn't done squat. I wouldn't have any worry except if someone turned the power up to the point of backward modulation or to the point of endangering component life.
CAROLINA PATRIOT Hi - I wanted to comment on - you said "Point of backward modulation or to the point of endangering component life". -I find that comment really funny. Back in the 1980's I worked in a CB shop, and the things that went on with setting up the Radios CORRECTLY, into 50 watt drivers- then into HUGE amps to the point of just what you said. Although set up correctly, you will not get away from all the harmonics and parasitics. And burnt finals. I mean these guys sounded loud and I made sure the radio wasn't distorting - I was on C.B. back then as well. Thats where the scope and monitoring your modulation, as well as a spectrum analyzer comes to play and is SO important. To each guy that wanted their stuff set up, I had to explain that they will be as loud as they want but (WHY) I won't make them sound distorted- and there is a fine line there. You can tell if they're set up correctly by their sound of course. However at home, I had a scope set up to see everyone's modulation (via 455kc in mod. from a C.B.) and would call them into the shop or tell one of their buddies to let them know ASAP, so it can be checked and fixed for free if possible. It was a cool thing actually and great for business. Good times.....
Now that one I think I can do, the other one, well I don't think so:-) great video as always, thanks
Excellent.
I just use a scrap bit of wire, wrap about 4 or 5 turns around the coax or one leg of ladder line and clip the oscilloscope probe clips to the ends of the scrap wire. The wire acts like a "sniffer" and picks up a little radiated signal. Its good enough to observe a waveform to check transmissions with. Down side, its not calibrated, but I use this to set up WSPR transmissions to very low levels, and ensure a usable (readable) signal. Hope that helps Kevin.
Useful Nice video.
Congratulations!
Wonderful video.
73 de VA6POP
Awesome, thank you!
Wow that is cool!
Another perfect video I've been looking for sir. Thank you sir. Keep em coming.
Can you do another video on using the bird 43 and slugs please and thanks sir
Seek and ye shall find: ruclips.net/video/149AuSmk4M8/видео.html
This is pretty cool. I was thinking I could use this to check the quality of the signal of my TinyTrak3, after it goes through the HT.
Fantastic video. I'd like to see some examples of what to look for in terms of "flat topping" and other errors that show you're signal isn't what it should be.
EXCELLENT PRESENTATION......TNX NN6AA
great video, I would love to do this. Thanks.
Cool idea - I think I'll present this idea to my club as well. We have guys who have no idea about ACL, and like to turn everything to the max. Perhaps if they see the shape of the signal, it wil get it through their heads what proper levels mean.
excelent !
Interesting. I am a Ham operator and just got my first oscilloscope so I might have to make this just to have.
Good morning, and to think that I just wrap a little wire around my co-ax to check my transmissions! Put the ends in the scope input and bingo, a small RF sample can be seen. But your circuit is certainly much better. Just goes to prove that there is more than one way to skin a cat, so to speak. 73 & 501.
"Puff" is what we've used here since I first heard the term back in 1959 (got my Novice ticket). The term is still widely used today as well.
Great Video Thanks, I am just about to install a scope into the shack.
Great video explanation. Thank you for sharing this knowledge. N2QPP
Sorry, I read W2AEW's connent and answered my own question.
But again, great video.
Useful. Thak you.
Great video ! I really enjoyed it.
Will you stil get a trapezoid in the SSB mode?
Nice vid, thanks, Sure is a nice scope, locks right on to the signal.
DAVE W4GSM
Though I agree with your analysis that most of the input voltage appears across the 47K resistor in the 690R load case, and it is probably true also for most attached CRO loads, the implication that the circuit could withstand 70V RMS is flawed. The 1N34A PIV rating is 65V, so it would be unsafe to operate it above say 20V RMS (or 8W in 50R) allowing a margin for safety.
i have an old scope, but had so much frustration with it to check the 4mhz signal, even when using a DIY highpass filter, i think my problem was trying to use the stock probes, they pick up too much AC noise, i guess i should run a coax from my circuit to the bnc plug
Great video there, i am getting my shack done up and gone get my test equipment out and vids like this are good to see and give me ideas thanks, how would you couple a 2 tone signal for 2 seprate generators when checking flat top in SSB ?
Just found your channel recently. Thank you for the effort you place into sharing your knowledge and the time it takes to produce the video's for RUclips.
I just bought me a scope in the past couple of weeks and I'm beginning to understand how to use it in my station.
A couple of questions:
1) are you using your scope probes to measure or are you hooking up directly from this board to the scope?
1a) if direct; is the coax attenuated in any means or strictly a straight 50ohm BNC coax like I might have lying around in my shack?
2) you stated that you were measuring a QRP rig. Help me here as I've been an Advanced class for 25 years but as an "appliance operator" only. Now, since I've retired, I'm trying to build me a few antennas and get some more theory behind me. With that... How would you determine value for resistors (wattage value that is) for say a 100 watt rig, a 400 watt rig, a 800 watt rig... all the way up to say legal limit 1500watts?
The main reason I asked (2) is I have purchased an amplifier (Ameritron AL-811H; 800 watts) and I would like to make sure that I'm doing ok with it.
The Scope that I bought is a BK Precision 2190E that I bought from Mouser. (I'm lucky enough to be near Mouser (1/2 hour drive) so I can order and pick up in same day.)) It's a digital 2 channel 100MHz bandwidth; 1GSa/s which for the price ($399.00) I thought was excellent.
Russ
KW5KW
good on QRZ
For monitoring 100W+,. I would probably not use a resistive tap like this. Take a look at my video(s) on RF Samplers / Taps for some ideas.
ruclips.net/video/0Kk_N_TpDeo/видео.html
ruclips.net/video/2D83xp3H5Bo/видео.html
Very interesting. Thanks for the demo.
How many scope do you have in your "shop/shack" there? Looks like a bunch that's for sure. Keep 'em coming. Thanks.
See...apparently I am really screwed up in my understanding of the basics.
To explain a bit my lack of understanding. I got my EE in 1982 and really never used it. Got laid off from Motorola in 1983 and never went back. I got my last ham ticket in 1973 and after a stint in the Air Force and life being what it is, got out of ham radio for about 20 years. So I have retired and have experienced some renewed interest but truthfully, this shows me how much I have forgotten or perhaps never knew.
Very cool! Thanks!
73 de KD0FNR Hamilton
Again..thanks....
Could you put something together for tuning a 2 meter band pass band reject duplexer, using a tex.465 Scope?
Your video's are the best on youtube.
The Tek 465 scope really isn't the best tool for this job. It is only a 100MHz scope, so the response will be down several dB at 146MHz. It doesn't have a 50 ohm termination, so you'll have to provide a through termination at the input. Even with this, it will be nothing more than a glorified RF power meter that you could use to peak/dip the pass and reject cavities, assuming you have an appropriate signal source to drive the cavities with.
Thanks for the great video, Alan! Not only is this a nice and simple mini project for a weekend or a night after work but it also gives you a great tool for testing AND for general learning for those that are relatively new to all of this, like myself. So, thank you!
I do have another mini-project idea though if I may suggest it? A CW practice oscillator. Yes, you get buy 50 different kits for this from Guang Dong Ding Hung Lo Province on Ebay and you can also find many different schematics online as well. You though have a great method of teaching and showing a lot more additional information and show how simple pieces of kit, can be used other places as well as how the end result actually works.
Anywho.....if I had a simple short list of things I would like to see you do. A CW practice oscillator with adjustable tone and volume would be awesome. :-)
N0BPS
+Brian Streufert Thanks - I'll add a code practice oscillator to my list...
+w2aew Thank you! Though I would venture a guess that your "list" with regard to videos you want to do and others want you to do is as long a your arm. I appreciate you even entertaining the idea and its always nice when a YT creator responds and interacts with their audience. So, thank you for that as well!
+Brian Streufert Yeah, the list is pretty long - several pages in a notebook. The CW practice oscillator is interesting because it may be a good venue for something simple like a phase shift oscillator...
+w2aew Well I am glad I was able to make a suggestion that caught some interest! Whatever you chose to do I am sure it will be great, thanks Alan!
Perfect and works well. Only subject you didn't address was the two tone, but, I guess thats a different circuit ?
I have two other videos on two-tone testing:
ruclips.net/video/3DxBg6h4Fc8/видео.html
ruclips.net/video/i29pI7okLe4/видео.html
Very informative and well presented, was looking to buy a ready made unit to do this with my FT817nd and my old Tektronix T935A but as you have shown it is so simple I will build my own, thany you very much.
How about a simple tone generator to go with it?
73
Phil M6MRP
Neat!
Great ideas for using an older analog scope as a station monitor. You can never have too many oscilloscopes, right?
Issue was with the diodes and one capicator. Box works great now.
Using a 40 DB attenuator should work nstead of the resistor divider?
That way in case you forget to turn your hundred watt transceiver down. I just want to double-check because would love to build this circuit. I do have a 40 DB RF attenuator so attenuation is not an issue.
Another question would be if I actually attenuated by 40 DB before I even hooked to that box would it affect the AM demod?
I have learned a lot in your videos are very helpful. I am looking into starting to play with radios and maybe work on them just for fun on the side. Just want to have the facts right since nobody else seemed to put them on the Internet. They talk about what they're doing but they don't tell you how it's hooked up. Thank you very much for the informative videos definitely will looking forward to the future ones.
I should add into this as well what kind of setup I will be doing. It will be transceiver to the dummy load. In between those will be a coaxial T to get my RF tap. then it will go through the 40 DB attenuator into the circuit. so will not be a feed thru but more or less acting as just a tap. Hopefully you can visualize what I'm saying. I am bad with wording.
73
ad0am
If you've got a 40dB attenuator that is rated for the power of your transmitter, then that is a fine way to go.
I built this circuit and tried it out on a digital scope (Rigol DC1102e). The digital scope give a different look than Alan's analog scope. I posted a video response, if you want to check it out.
Were the capicators used specifically for 40 meters. I built the same sampler but I get some RF in the detected signal. Using on 11 meter band. I have photos but don't know how to sent them to you.
Have you thought about selling a kit? I'd but one. Thanks for the video.
Cool to do... I wish I could afford one.
Great vid.i wish i could figure out the settings on my scope to get ssb to read correctly
Typically about 1ms/div horizontal, trigger source set to LINE. Vertical scale as needed, typically about 10-100mV/div.
@@w2aew thank you will try. Im alittle scope challenged..73
I have just about watched all your videos and have thoroughly enjoyed everyone. I have just acquired a scope and am looking for ways to learn more about this wonderful hobby. I am in the process of building this project but on a breadboard so I can do minor substitutions of parts to see the changes. Do you have any warnings?
I have a couple pieces of advice:
1) Do not build it on a plug-in breadboard. These do not work well with RF.
2) Be careful about the power rating of the resistors used, depending on the RF power you plan to run. Calculate the power rating needed for the resistors.
3) Do not built both the sampler and demodulator on the same RF tap like I did here. I did it only for convenience. They would never be used this way. Build them separately if you intend to use them for rough linearity checks.
4) You will likely want to put an attenuator ahead of the demodulator for two reasons - to limit the voltage peaks seen by the diodes, and to limit the amount of distortion injected back into the RF path from the detector circuit.
I have a few other videos on RF samplers that you might want to view also.
***** Thank you very much for the advice. I will heed your cautions with great care. So far, no smoke. :-)
Thank you..I am just hoping to find someone with whom I can dialogue to help me understand how Alan calculates the power dissipation. I would like to understand this very much but...alas..I am not very experienced and have never had much practical experience. I would be appreciative of your help.
I am having difficulty getting the trapezoid reading. I have Dmod to X as indicated by your notation. Sample in Y. GO into X-Y mode, and instead of it going left to right, it goes up and down in a fine point. I have tried swtiching the x and y channels. Everything else seems to be working as it does in your video.
NM, I just figured it out. On my scope I have to plug X into EXT.
Thanks for this, I might dig my scope out now :)
Can this be added to my ATU, taking the transmitter input as the source?
A couple of BNC sockets on the back would make it useful, what happens if the BNC's are not connected to the scope - can it be left inline?
Matty Lad If you have a ATU with unused ports, you can use the technique shown in this video, super simple:ruclips.net/video/2D83xp3H5Bo/видео.html
No direct connection to the RF line, nothing to build, works well. Just heed the warnings in the video.
@nflgun In addition being able to monitor the RF waveform when running BPSK3 would be advantageous since it's difficult to set your drive levels without someone else observing your IMD. Question, what kind of waveform would you get if you drove the Ext. trigger with the demod signal? Any chance you'd consider refining the circuit some and maybe writing a QST article? I think you'd be surprised at the response.
Cool vid..ive been trying to set one of these up but cant get settings right for ssb monitoring
Here is one simple way to do it!
ruclips.net/video/2D83xp3H5Bo/видео.html
Thanks, Alan, this is just what I need to test my new transmitter (Icom IC-7300) before making my first QSO. Although I can follow your very clear explanation, I'm confused when you say (paraphrasing) "to be sure to size the resistors to be certain they can handle the power they're going to be sensing". I assume your QRP rig is putting out 5W and my 7300 is putting out 100W into a dummy load. But without voltage or current information how does one calculate the power that will be dissipated by the resistors? Sorry for the newbie question. JS2OLO
At 100W, you're likely going to be better off using other sensing methods rather than a resistive tap. See my video at on RF Samplers...
Another way that I reasoned was to think of the RF current passing through the 47K resistor and then splitting between the parallel combination of the 50 ohm and the 690 ohm resistor with the 50 ohm carrying the bulk of the current which I calculated to be 1.414 amps rms. So wouldn't that mean that at least 1.414 amps would be going through the 47K? Looking at I^2R dissipation wouldnt the power dissipated be more than 1'2 watt?
Thanks for the share. Just got done building the circuit, but performance isn't what I expected and have some questions hopefully you can address. First thing I notice is that it doesn't seem that useful for sideband. Applying two tones, if I change the modulation, I just get a larger or smaller triangle, but the triangle itself doesn't change shape. Is the trapezoid method meant for only AM use? I see dual triangles opposite one another which may be more useful, but not sure if this circuit can do this.
Another thing I notice is that I can't seem to overmodulate. I increase mic gain and/or tone generator for maximum on AM, but whether the trapezoid or sine wave, they reach maybe 90-95% and go no further. Could this be due to the radio's internal ALC setting?
When I first tried the circuit, I was getting "bitten" when I tried to adjust the tone generator, then I discovered that I had RF sampling going to channel B and modulation sampling going to channel A. Switched them and I don't notice any "bites" now. Does hookup have to be as you did to avoid this issue (RF to A, modulation to B)?
My radio has a built in SWR meter. I notice with the modulating sampler inline, SWR on the radio increases to around 2.5. If I just use the RF sampler, under 1.5. Any ideas why the increase? Note that I didn't build it the way you did. I have a separate small box for RF and another for modulation sampler.
My voltage divider, borrowed from an existing one I made years ago, is 20:1. Does this matter? I also don't have a 0.01 uF cap at the output in mine, just the resistors. Should I add the cap?
Lots of questions, sorry, but new at this sort of thing. Just trying to do it as accurately as possible and thank you in advance.
As described in the notes below the video, this circuit - as shown - can NOT be used to measure non-linearity with the trapezoid pattern since both the sampler and detector are fed with the same RF signal. Refer to the notes appearing below the video. This circuit, as shown, is only suitable for QRP levels of power. See my other videos on RF Samplers to get some ideas for higher power RF monitoring. Yes, both the RF sampler and the detector WILL affect the SWR.
I am wondering about the 1k across the demodulator. This would give a very high cutoff surely? The time constant with the 1000p cap would be 1uS. I tried your circuit out with the values shown and found that sure enough, pretty much all I could see was residual RF and no AF. Increasing the value to 47k gave a good result, nice clear demod and very little RF on the signal. The results are clear but I do wonder if my thoughts are all wet?
+984francis The 1K resistor is just to provide a bleed off path for the charge stored on the 1000 pF capacitor. A higher value will give a slower bleed off rate, and will work fine for demodulating audio frequencies. You're results are fine - simply choose the values to suit your application.
Alan..I had written you a couple of days before and was interested in how you would calculate the power dissipation of the 47K and 690 ohm resistors needed for one leg of the RF sampling circuit. It seems to me that the resistors would have to be significantly more wattage than 1/2 watt. I certainly understand that you are extremely busy, so if you could direct me to a source that might help I would also be appreciative. I got my EE in the 1980's and never really developed the "knack" . Thanks
Sorry keep bothering you but I think your the best teacher for electronics I am looking at this one
Tektronix 2465BDV 400MHz is it a good deal for 300.00 thanks
I think the 690ohm resistor should be 680ohm as 690 is not a standard resistor. I might be wrong. Kind regards Spence
PS: Great video as ever
Calculate the voltage expected across each resistor. The power is the rms voltage squared divided by the resistor value, P = E^2/R The resistor ideally would have a larger power rating. For non-QRP, the diodes or 10pF cap may not handle the peak voltage. You could attach the diodes at the divider where the voltages are much lower, or build a second divider ahead of the 10pF cap.
This is awesome! Could this concept/configuration be use to monitor a stereo receiver output?
A fun thing to do is to put the scope in XY mode and apply the right and left channels to the two inputs.
@@w2aew Thanks for responding Alan! So with your attenuation device, no danger to the scope? Also, I have an old Sencore vector scope I can have some fun with... Thanks again and looking forward to your next vid!
Good morning. First of all I want to apologize for my bad English. My question is what is the capacitor value of the RF sample, I don't understand its value... 10pF?. 0.01nF?. It has to be plastic and not ceramic? I loved the video, I have an SM-220 from Kenwood but in the second QTH I want to put the same thing but with an old oscilloscope that I have several. Thank you very much for your answer dear friend, a great teacher although I have a hard time understanding the details by the language.
There are better ways to do the RF Sampling. Check out these videos:
ruclips.net/video/0Kk_N_TpDeo/видео.html
ruclips.net/video/2D83xp3H5Bo/видео.html
Alan, please let me go back to basics: I was thinking that the 100w generator "looked into" the "rf in" on your diagram and saw the 47k in series with the parallel combination of 690 and 50 (which is the o'scope) with both the 690 and the 50 tied to ground. Is this wrong?
Hello, congratulations, very usuable device.
What is the max. input power? what is the attenuation on RF port?
What is the max operating frequency¡?
73´s de XE1XNP
Thank you for your response. . Are you saying that the advice is conflicting because, in fact, the scope input Z is not 50 ohms?If the scope input Z were 50 ohms then the 50 would be across the 690 and that would act like a resistor of 46.62 ohms in series with 47000 ohms thus the 1:1000 voltage divider. But as I understand it you are saying that in fact the input Z is more like 1 Mohm and so the voltage divider is really more like a 690 in series witth the 47000K. Am I understanding what you ?