Cheap DIY RF detectors

I came across a couple of videos some might find interesting:

1) Point contact mixer diode 1N3747 used for DIY RF antenna.
https://youtu.be/xYjEkg7FuM0

2) Simple RF Detector with a detector diode and an LED.
https://youtu.be/vHVmJ5lD9jc
(This person does not believe in EHS, but makes interesting videos, he has a couple more).

i actually went looking for that 1N3747 military surplus mixer diode, but I think the only stock comes from people salvaging old equipment.  Amazing how simple the circuit is.  Magic!

My long-term fantasy is that after the election season is over in 2020, we take all those useless lawn signs for candidates and repurpose them into RF meters with red/yellow/green LEDs.  If everyone in a neighborhood had one it would be much more obvious how pervasive those signals are.  The 1N3747 video sparked my hope, but I am not yet handy enough to improvise on this idea.  But some day maybe ...

Fog Top wrote

Very interesting videos, Merializer!  Now I wonder why a plastic German high-frequency analyzer cost me $400?

The Gigahertz and Cornet meters are supposed to be calibrated; so if you and I both test the field strength around the same microwave while it's running, we should both get roughly the same results - even if my meter is a Cornet and yours is a Gigahertz.

I'm not sure if that's true.  I got some weird readings with my Cornet, and eventually the RF mode stopped working altogether.  It also never told me the frequency of the signals it was detecting, which it's supposed to do.

So maybe having separate antennas for each of the common frequencies and hooking them up to a microamp meter like the one in Merializer's second video* is the way to go.

*They're cheap:  https://www.jameco.com/z/AIM60005-Velleman-Analog-CURRENT-PANEL-METER-50UA-DC-60-X-47MM_315301.html

Here is some more information on designing/building these:

https://www.qsl.net/g3oou/simplerfdetectors.html

https://en.wikipedia.org/wiki/Envelope_detector

I think it would be possible to make a meter with a few of these tuned to different frequencies, and a multi-position knob to switch between them.

FWIW, I bought some specialized detector diodes that are supposed to work above 8 GHz, and hopefully will be able to use them to detect car radars and 5G transmitters at very close range*:

https://www.skyworksinc.com/-/media/SkyWorks/Documents/Products/201-300/Surface_Mount_Schottky_Diodes_200041AE.pdf

https://www.skyworksinc.com/-/media/SkyWorks/Documents/Products/2001-2100/SMSA7630_061_203200D.pdf

The first one is rated to 24 GHz and is tiny - 1.6 mm long including the pins and 0.8 mm wide.  The other is rated to 77 GHz and is even smaller.

They're designed to be used with a technique called reflow soldering, but I think the easiest way to experiment with the larger one is to insert it longitudinally INSIDE one of the holes in a piece of phenolic perfboard, then attach short copper strips to each side of the perfboard to form the dipole antenna like the one in Merializer's second video.

* If it works, it probably still won't be sensitive enough to pick up a -40 dBm signal.  But it could be handy for determining if the 5G antenna in WiFi router is really disabled.  Or for locating the adaptive cruise control radars in newer cars.

I made a tiny little radar detector using one of the 24 GHz diodes:



For the moment I stuck it to a piece of clear tape, then added 0.001" thick aluminum foil strips to form a dipole antenna tuned for 10.5 GHz.

It's not sensitive.  I get 50-100 mV between the two sides of the diode when I shine an HB100 radar transmitter at it from a few inches away.  But since there's almost no voltage between the two sides when no radar is present, any signal strong enough to generate 5 mV would be detectable.