Sensitive RF Field Meter Circuit - Pinpoint Transmitters
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- Опубліковано 10 жов 2013
- Very simple but handy circuit to have when testing/adjusting FM transmitters. The circuit shown uses a minimum amount of components, and when using the correct meter(100uA), it is extremely sensitive and can be used for pinpointing hidden FM transmitter locations using the zeroing knob. Schematic can be seen in the video. This circuit detects the energy emitted from my cell phone better than my expensive tri-field meter!
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Great tutorial and works great! I used a 100uA meter I got from an old metal detector and a 10-turn 1K pot. The multi-turn pot makes it much easier to zero in. I also tried a 500mA gauge which worked, but was less sensitive. I attached a telescoping antenna which increased the range dramatically to several meters away. I had to turn the sensitivity way down. I used a fixed 100nH inductor in the tank circuit with a germanium diode and a 820p cap. The JFET is a J211. I'm using 9V, but I was able to get it working with proper sensitivity at 3V. At 1.5V it lacked sensitivity. I'm using it to adjust an FM transmitter I built based on the UA-cam video "Quality FM transmitter" from andydaviesbythesea, to which I've added a power amplifier stage. BTW, I also copied your square loop transmitter, which works very well, and your mains-powered LED indicator. I use it to monitor my soldering iron so I remember to switch it off...Thanks again to all of you who provide informative videos.
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After some experimenting I've realized the antenna impedance of the transmitter and meter need to be matched. When I get some connectors I'll follow your suggestion and make detachable antennas for the meter to swap out as needed.
It was designed for VHF/UHF, but I don't see why it would not detect HF. I would experiment with different value coils. Maybe 2-3 turns of 20ga wire around a 1/2" form. Also need to make sure the antenna is the proper size(1/4 wave or 1/2 wave) for the strongest signal detection.
Brillian! :D
Got it working all the way down to 3.5 MHz, prob a bit lower. Really worth the time to build.
Beautiful job! I have to biuld one! Cheers from Australia
It's a fun little project. :-) Be sure to rate thumbs up, subscribe, and look over my extensive video playlists below for many other videos of interest to you. Taking one minute to share a link to my channel with others on social networking sites would be greatly appreciated. Thank you!
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Many thanks great tutorial. Acquiring JFET 2N4856 and 100uA class 2.0 ammeter to build my very first RF Strength Meter.
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Sure, thumbs up ! Btw, will JFET J310 able to fit well ? RF/VHF/UHF amp or 2N4391 ?
Not sure. You can check using this below, or you have to look up the data sheets and compare them.
nte01.nteinc.com/nte/NTExRefSemiProd.nsf/$$Search
Yes, comparing the data sheets now.
I have a couple old CB' radios I could salvage parts out of . ANY Advice and or tips would be much appreciated .
I find the size of the antenna needs to be roughly the same size as that of the transmitter I'm detecting. A
full sized telescoping antenna detects my 17'' ground plane transmitter antenna, but I need to use a small wire antenna to detect an FM bug transmitter. Any thoughts?
Can we replace with bjt or mosfets ?
Can I use an schottky diode instead of germanium one for better sensitivity?
No
What about HF 30MHz and below?
How about 50 uA panel?, I couldn't find 2N4856, which values Is the important in the data sheet for finding an equivalent transistor?
You can try it, but it's way too low. Use NTE's website to find an equivalent transistor. Thanks for watching!
Anyone know how to detect a 500 htz signal and help me out?
500 khz? Try modifying an old AM radio. :-)
@@electronicsNmore I do sewer work and need way to detect my 512 htz sonde. They have a reciver wand but that thing is like $1200
I used a am radio and it sorta works but super weak. Is there any way to detect that thing from above ground without spending so much
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I love your videos, but I don't think those fancy new graphics on the intros go with your style. They are cold and modern, and your style is warm and friendly. The graphics push me away and your style of presentation draws everyone in. What if you just used a piece of paper with the video title on it in big letters handwritten. Then that would go with your style of presentation which I think is just outstanding. And I like your choice of circuits.
I find the size of the antenna needs to be roughly the same size as that of the transmitter I'm detecting. A
full sized telescoping antenna detects my 17'' ground plane transmitter antenna, but I need to use a small wire antenna to detect an FM bug transmitter. Any thoughts?