Cell phone detector circuit modification

Thread Starter

MCH170

Joined May 13, 2021
12
Hello, I want to build a cell phone detector circuit. I searched on youtube and found this to be the best video explaining how. I was wandering where can I connect an antenna (also what length does it have to be) and which component(s) do I have to change in order to increase the circuit's sensitivity/range. Thanks for your time.

YouTube video I found:
 

scorbin1

Joined Dec 24, 2019
103
I hope you are not looking for something extremely accurate. This circuit will absolutely not discriminate between a cell phone and other RF devices operating close to the same spectrum. You could tune the device to filter out other bands known not to be cell phones, but what's left over is a pretty good sized spectrum. On top of that, there are several different, and considerably spaced, bands that cell phones operate on depending on location. For this device to detect ALL cell phones, it will need some fairly sophisticated circuitry well beyond the scope of the tutorial you show.

This sort of looks like the circuit in the old light up cell phone antennas with an amplifier added in. Those will generally flash when fed with an RF signal on almost any band. It may well detect cell phones, but it's likely going to detect MANY other things as well, like WiFi, bluetooth, and microwave ovens for example.

Sensitivity and filtering would be adjusted by modifying the associated component values around the OP Amp. Those values would depend greatly on the exact frequency range you are wanting to detect and how much amplification you imagine you would need. Still, I don't think you are going to get very good accuracy. I am guessing that at the point where the sensitivity becomes useful for moderately distant devices, it will also become useless as it will likely pick up just about anything giving off RF noise.

Just my two cents, and not to be taken as fact. Perhaps someone else will chime in and confirm or correct me.
 

MisterBill2

Joined Jan 23, 2018
12,704
I discovered that an older police radar detector will detect cell phones quite well, at least the one that I got would. So I could know when anybody within a few hundred yards was using a cell phone. That was 15 years ago, now cell phones use several different bands.
 
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