Electronic – Simple high frequency (GHz) RF radiation detector

frequency-measurementhigh frequencymicrowaveRF

I want to build a simple RF radiation detector that shows if there are any RF devices transmitting at a certain frequency. I want to use it to detect RF radiation in the 2.4 and 5 GHz range. I have a 1SS86 diode which works at high frequencies, a MMBR941 HF transistor (works up to 8Ghz) and a 2SC3356 transistor.

I also have a DC ampere meter (range 0-100uA) which I would want to use to measure the signal strength. Or I could use an LED instead. Or better I could use headphones to measure the radiation intensity as sound.

Basically I want to extend the range of this device (I think it's called lectenna.)

I tried to build it myself like it was shown in the video and the LED and ampere meter only detects the radiation when the 1SS86 diode is near the Wifi antenna (the meter shows a 10uA at a distance of 10 cm from the antenna and spikes up to 100uA when I move it right near the antenna). But if I move further away from the router, like more than 15 cm away, the meter does not record anything. So I thought that I need to somehow amplify the signal so thought to use a transistor but that did not work for me so maybe some of you could help me?

For the 2.4GHz I use a dipole antenna with a total length of about 5.9cm (2.95 cm in each side), like it is shown in the video. I do not have a variable capacitor to create a LC circuit so I am using fixed length of the antenna in a hope that this can bypass the use of variable capacitor.

If I absolutely need to create a LC circuit, I can build the coil myself and for the variable capacitor, I could try to make one using aluminium foil and paper like in some Youtube videos although I am not sure that it will work at such high frequencies.

This is what works

Best Answer

The ISS86 diode has a capacitance of 0.85 pF and, at 5 GHz this is an impedance magnitude of 37.45 Ω making it pretty unsuitable as a diode detector because, in the forward direction, it will rectify (what you want) but, in the reverse direction it will still have high AC conduction due to the 37.45 Ω capacitive reactance.

The MMBR941 has an \$f_T\$ of 8 GHz and this means that at 8 GHz the current gain has dropped to unity. At 4 GHz the current gain will double to 2 and, at 2 GHz \$h_{FE}\$ will be 4. In other words a fairly poor device for your targeted operating area.

The 2SC3356 has an \$f_T\$ at 7 GHz. Enough said.