Let's Build A Field Strength Meter
HTML-код
- Опубликовано: 13 сен 2024
- I follow Richard's, KB3VZL, February 2015 QST (page 71) article about building a field strength meter into a DVM. He built the circuit to fit inside a Harbor Freight digital volt meter. You can get these free at Harbor Freight if you have the right coupons.
I also use my new ISO-TIP battery powered soldering iron.
www.iso-tip.com
Three capacitors, two diodes and a pot is all that is needed. Build this on a small perf board and it fits easily inside the meter.
Parts:
0.05 uF Cap
470 pF Cap
0.01 Cap
1N34 Diodes, you need 2
50K trim pot
hunk of perf board
switch
connector for antenna
I don't believe I have ever seen a circuit built on an upside down perf board! Whatever works right!
@JOSEF BORG You are the borg don't assimilate this guy he does things upside down...
What a fantastic simple project for a "ham in waiting for the ULS to get updated". Thanx, Randy. Am enjoying learning from your experience.
Thanks, Randy, that's a great way to use an old meter that we have lying around. After a while they tend to breed like rabbits - I must have collected eight or ten of them over the years, both analog and digital, most now in various stages of disrepair. BTW, you probably know that the Iso-tip soldering iron isn't new. I had two of them back in the mid 1980s. Mine were made by Whal and were powered by nicad batteries, but neither lasted long as I recall. The tips kept breaking, especially when dropped, and the batteries had too little capacity. Maybe they're using nimh cells now. They were, however, good for field repairs if care were taken in their storage and charging.
I have made it with 1n4148 diode, and set the meter on 200milivolts range, its working fine, Cool Project. Thanx sooo much.
I have an endfed wire antenna that I use on several of the lower bands. Transmitting 100 watts max output, so of course there is a bit of RF in the shack at times. A field strength meter is very useful in sniffing the RF and helping to know how to arrange cables, power leads, installing ferrites, counterpoise, etc. in order to keep RF away from keyboard, mouse, etc. It may be a little "old school" but I simply placed a germanium diode across the terminals of a Simpson model 374 microammeter. No antenna lead necessary- it is plenty sensitive. Just move the meter around to hunt the RF hot spots. Very handy indeed. (And no batteries required, haha...)
Thanks Randy for another handy project and the tips on getting the meter. This mod should work with other meters even an old analog. Nice that the switch lets one use it as a field strength meter or multimeter. Good job.
Bob McClard you are correct
Hi folks, don't knock Randy for putting those parts through the opposite side of the board, it does have its advantage, because the printed circuit HOLES are copper, and RF can jump to each of these because they are so close causing interference from stray RF signals outside the meter, and adding a miniature DPDP switch to disconnect both the + and the -- will keep the user from electrical shock when measuring high voltages.Thanks Randy, great job.
What a great job, Randy! I love what you're doing, helping keep ham radio a hands on hobby. So many new hams today can't build anything and know very little about electronics.
Rick W0SKI/7
thanks
Thanks Randy well done ! I built one and it works great much more sensitive than my old heathkit field strenghth meter picks up my 1 watt two meter HT at a distance of 25 feet with a 19 inch whip on both . I did not have 1N34 diodes but did have two 1N295 germanium Diodes I don't know what the difference is but they worked fine I am thinking that just about any of the germanium glass diodes will work ok . I also eliminated the 50 K pot shown in the QST article just put a 100 k resistor there across the .01 cap figuring the meter has several Voltage ranges and in this case would not be required . 73 Bob W9RAS
Randy, great job! I'm planning on making a FSM, and your video was the first to pop up. I like the design of adding this into the HF meter. Very cool!
FYI - that Iso-tip link is not valid any more, it apparently goes to a malware web site.
Hey Jim, I just had the same thought today. When I saw Randy had done it I clicked him first also.
I have one of the original's from qst and it uses an analog 1ma ge meter. Its pretty sensitive. Good that this one uses germanium 1n34 diodes for best sensitivity. i'm going to build one inside this same box with the analog meter, but it will add a little .96inch digital display. I'll use an i2C circuit and probably an arduino nano. So it will be an analog/digital hybrid.
Great as usual...gotta love the "lava light"...
the lamp is great
Randy, love all your videos. New ham (KK6VZD) in Yuba City just breaking into playing with building electronic projects. Yours was easy for a beginner and it was a kick to see it actually function when I finished it. SInce the only toggle switch I could find was a double pole I used the extra pole to add an LED to the top to indicate when the circuitry is engaged. Only question I have is what to set the 50K pot to, not in your video or the original article. I think I ended up adjusting mine to 10k. Next step: put together another FSM from different plans using analog meter.
+Chris McLain The pot is just used to set the scale, which isn't really too important. Sounds like you had fun putting this together.
I now regret throwing out two old ultra cheap mms a couple of weeks ago that I 'made do' with when I first got back into the electronics construction hobby after a thirty year hiatus 😀
And this is how to create cold solder joints
Inspiring. Thanks for another great lecture.
Nice project. Time to dig through the parts bin.
Digitial volt meters are made to a safety spec (CAT 11) Thats to protect the user. Adding external metal work with internal connections makes the meter unsafe to the user when making normal voltage measurements to the maximum, under fault conditions a user holding the meter in hand could be touching the external metal work and recieve a fatal shock.
Good point
great video, this will be my first Electronic project. Exciting!
Hope the build goes well
A very nicely done project and at minimal expense. I wonder if the circuit can be further simplified by eliminating the pot and the capacitor right at the meter terminals. And, I wonder if Schottky diodes would work just as well; since they too would have a very low forward voltage drop at these tiny rectified currents, and their capacitance would be very small compared to the disc capacitor values used.
Sure, try all those ideas and see how it work.
I built it with banana plugs on the back. Just plugs right in when I need it. Made to fit my $100 multimeter.
Good idea
LOL, this field strength meter has been one of the most interesting projects i have ever done. Probably the simplest and cheapest, but definitely the most interesting. I have probably done something wrong in the build, but i think it may be more useful as an GHOST detector, or maybe some kind of light power tester....LOL It seems to shoot up in value when i get just the right distance from a light.... as long as i am transmitting on my HT. it also seems to work no different if i disconnect the red wire from my circuit board????? so that may be a clue to what i have done wrong , but i still haven't figured that out, even though i have built two of these for comparison but get the same exact results. LOL, if nothing else it was fun scaring the grandkids that it is a GHOST detector! LOL
+Hammer USN Are you getting close to a CFL or LED bulb? You could be picking up noise from the lamps. Have fun chasing ghosts.
Not wishing to be critical, but I cannot see how it measures field strength. It seems to just be an indicator.
I would also suggest that the voltage doubler circuit is not the best for small signals as it involves two diode drops.
Very neat project. I have to ask what camera you are using. Even at 720 it looks amazing- beyond amazing in fact. Do tell :) Great job. Cheers
Eric William Sony HXR-NX30E,thanks. New lights in the hamshack too.I tweak the black and contrast levels for each clip, gives it a bit more zip.
I agree, I'm only watching at 360p and the video quality is excellent compared to many other so called 360p videos out there.
good project, but need more tests! and check exact frequency field that this small circuit can detect, THanks
Good idea to install it into a DVM. Project for tonight! 73 VA7GTE
A very nice little project Randy. Thanks!
73 Simon -PD0KDN
nice video
Unfortunately I can't get germanium diodes in Australia. 🥺
Very cool project!
Randy, how does it do with HF in the shack, did you try that yet? I am interested in making a field strength meter with a buzzer if it climbs above a certain value. This will be a clue to something being wrong long before it becomes a bigger problem. I think it can easily be done by using an ATTiny85 controller, but only if the sensitivity is good enough the see HF RF in the shack..
I would love to see someone use this to test the effectiveness of adding a counterpoise wire aka "rat tail" to an HT. I have built a counterpose for mine but almost feel silly using it since I don't have any good way to know for sure if it works. Would also like to test rubber ducky vs third party antenna on an HT. This simple device would be great for these as relative is all we really care about.
Tracy Reed Sounds like an interesting test
Misleading, it does not check the effectiveness of a dipole vs. beam, for example. Distance from each would have to be the same, polarization of antenna would have to be the same and since you are on the ground take off angle would be different. In any event I have 2 of the meters, if I send you both will you make me a field strength meter, you can keep the other meter.
burt2481 It would still be interesting to test the antennas. I am really not setup to build meters. And, I have 4 or 5 of these DVMs.
K7AGE I have 3 of the meters. It is interesting that is why I wanted a meter built. But it does not do as you said ( check the effectiveness of a dipole vs. beam). Otherwise the video is useful.
+burt2481 do it yourself
+W3TFART You are right I should really listen to someone with FART in his name
burt2481 Yes you should 73
Randy, is there any special reason you made the antenna 19"? Would any length have worked just as well? Thanks, Larry DL8VKO
Hello, I K7AGE circuit generates the magnetic field strength meter thread.
Randy, how do you like the ISO-TIP soldering iron? Does it have a small tip for surface mount parts?
Ive had mine since 95 and purchased the needle tip for smd parts. when the original battery gave up the ghost, I replaced it with a larger capacity nmhi instead of a lower capacity nicad
Great video. I shared it with my Amateur Radio Club. I have 5 hams interested in doing the project. Cool right? Just wondering what the is the setup procedure for the potentiometer?
Since the Harbor Freight meter is a Digital Volt Meter with a high input resistance, I am assuming the detector module can be added to any DVM as an external module maybe with a spiffy custom case)?
You mentioned it in the video, but I would be careful about applying voltage to the DVM when the switch is in the RF Meter mode. Sparks could fly. Maybe an very low amperage in line fuse could be used to protect the user from a mistake or change the sub mini toggle changed to a momentary push button (both with the max rating of the meter's voltage range)?
Joseph Levesque I just the pot to the high end. I don't know if there is an method to adjustment. It may be a left over from the days of using an analog meter. Sure, you could build this in an external box. You can deal with whatever level of protection that you feel is needed. One guy mentioned that the meters are so cheap you could use it just for this application; You could fill the test lead holes with bathtub caulk to prevent plugging in the test leads.
Question: Does this work to measure relative signals from different types of TV antennas that can pull digital broadcast signals (UHF)?
Verry interesting. I'm kinda a butter fingers. Could I put the board in a box, and carry the box with the meter. And plug it in as needed? So That my box complements the cheep but fine meter? Kv4li (brushing 68 and not ultra stable. Hi hi ) 73 de kv4li
I cannot find the article mentioned online. Can you post it as a pdf? Thanks.
I've always enjoyed your videos--and lemme guess, somebody told you to smile. Ha ha. It was sort of your trademark, a somewhat dour-but-nonetheless-cheerful presence. Anyway, glad to see this excellent video. Best 73, W0XO
;-)
Great video makes me want to build one just to say I built one HAHA. Don't have a use for it, but hey putting some components on a board and soldering and getting it to work is always great practice anyways.
Warm up your iron
K7AGE I actually think I may need to invest in one of the new ones last time I used mine it didn't work very well but then again its 30 years old LOL.
Very useful, I want to try it someday. Tnx Randy.
73 de yc5nbx - J.Lesmana
Greetings, looks like a great project, I was just wondering if a fellow could use one of those little chinese volt meters all in one displays instead of hacking a multimeter? Should work, I use them on other projects all the them where I need voltage readout.
+Jerry Ericsson If they are sensitive enough. Give it a try...
Randy nice job but why you put the coper side up side down and don't use for better soldering?
Just a fail or is better like that?
ezquimal I didn't think anything about that, as I soldered the wired together, not to the holes.
Thanks Randy.
What would be the sampling rate, and how many Ghz does it go up to?
I would only use this below 30 MHz.
Hi,
Can any body tell me, does it measure signal strength of RFID reader?
Why have the capacitor on the antenna? I dont see a point
The two caps and diodes are a voltage doubler circuit
Would a 1N4148 diode work for this application?
sorry, no there silicone you need geranium.
Hello. I am looking to make a simple signal strength meter to use with my "quad bowtie" broadcast tv antenna (up in the attic). It is my hope that I will be able to orient the antenna for the best possible TV reception by watching the field strength meter as I move the antenna around. Do you think this little device would do the job? The channel frequencies that I am looking to receive are from 200 to 600 Mhz. Any thoughts? Thanks!
+Anon This meter would not be sensitive enough to measure the signal strength from a transmitter far away. Check in the menus of your TV, you might find a display that shows the signal strength to help point your antenna. If not find the angle to the left and right that the picture breaks on and center the antenna between the two direction.
+K7AGE Hi. Thanks for your input. I have been using the "back & forth" method of finding the best signal, but it does not really give me what I'm after. I think that my antenna might benefit from being tilted upwards slightly, but I'm not sure. I also have a few big homes sitting directly in the signal path so I'd like to try and find a "hotspot" n my attic. Of course, in the old days, I could just watch the screen on the TV and see the picture get better or worse, but those days are gone. Either the digital signal locks in or it doesn't. So, I would really like to come up with something that could be directly attached to the 75 ohm balun on the antenna and be used as a sort of signal strength meter which would cover the 200-600 MHZ range. That's where my channels of interest lie. Oh well, back to the drawing board!
+Anon Sound like you need a real CATV meter.. tinyurl.com/hvfn6g9
******************** I wonder what else can be made with a multimeter?
Will this measure field strength from a GHz output if capacitor values are changed?
I'm not sure if the diode will work up in the GHz freqs. Wire up some parts and connect it to the inputs on the front of the meter to try out.
Sir does it work for Detecting VHF Signal or fixing antenna at sweet point.. please Tell me
If you know how to use it, it does
Hi Randy, do you still have this copy? I am going to try this project but would love to read the article first.... any chance that you could scan a copy of in and link it here?
Thx
Steve
M7SAB
I'll look. What is your email?
@@K7AGE thx it is sbods@hotmail.com
Hey Randy - Just completed this project and it works well (not quite as sensitive as I would have liked but all good. Thanks for posting this and inspiring me to have a go!
ok sir, im at the soldering station trying to figure out how u tell which pin on the pot is hooked to which, im assuming it matters because one is the wiper ......i think lol
+Hammer USN The center is the wiper. If you have an ohm meter, check out the pins as you adjust the pot.
Ty, sir
+K7AGE ok, had to go back home for a few weeks, got back this mourning , and got mine working.... thanks, and i should be taking my tech exam , in dayton, in a couple weeks, thanks for all your help with everything, "ELMER RANDY"
Hard to find 1N34s these days
Yes, you need to hunt around. Try Shockley diodes. Silicon may work with reduced sensitivity.
I am getting readings in 0.07v for 4watt fm transmitter at a distance of two feet.when I almost touch the antenna of transmitter I m getting 1.5v whats wrong??
Maybe adjust the pot for a higher reading? I'm not sure where my meter is to try it out myself.
Nice KN4AWO
Why not build it plug in play to Jack's that come with meter
I don't see why not... Give it a try.
what would be a application for this, or is it just a fun project?
+Hammer USN This can show a relative difference between antennas.
+K7AGE OK thanks, the reason I asked was I built your vertical antenna , and was wondering if I would be able to tune it in with this field strength meter , or I guess I'll have to pry the wallet open for swr.... lol
+Hammer USN this isn[t for tuning. You'll need an antenna analyzer for the antenna tuning. $$$
Great job the lower scales on the mtr works better 4 me i used a mini slide switch every ham should have one tnx randy bcnu on ham nation 73 kg6mn
too long, tooo slow, toooo blablabla
Hello, I K7AGE circuit generates the magnetic field strength meter thread.