Electronic Eavesdropping Devices Detector

[yourwins]

http://www.electronics-lab.com/projects/rf/005/index.html

Can Transistor( BFR 90A ) replace with other component  and
        Diode( NTE 112 ) replace with IN4007  and
        IC (

[Ante]

Yes all of them can be replaced. As long as they are equivalent in data.

Ante

[yourwins]

Can Ante Specify that parts for me ?

[Ante]

yourwinns,

The BFR90 can be replaced with BFG90, BFQ28, BFR14, BFR49.

The MC3403 with LM324

And the NTE112 is a TV UHF Mixer diode can be replaced with BA481

Ante

[sargehendricks]

I am a new electronics hobbyist, and I am very interested in this circuit for use in a current investigation (can't elaborate much).  Anyway, I am looking for a schematic like this that will detect up to 3000MHz.  Therefore, my question would be: How do I modify this schematic to detect up to 3000MHz?  I pretty new to any kind of RF electronics (building).  Thanks for the help.

[audioguru]

Hi Sarge,
Welcome to our forum.
You are talking about detecting very high frequency microwave frequencies, where a short piece of wire is a tuned circuit and a short piece of metal is an inductor. Therefore a special wiring technique must be used (waveguides) that resembles plumbing.
Also, parts that operate at high microwave frequencies are not readily available.

This simple circuit is not tuned and would be overloaded by every radio and TV station, taxicab radios and anything else that transmits nearby.
Good luck.

[jason]

Hello there,

Just like sargehendricks I'm quite new to this stuff. (cannot elaborate on the purpose of constructing the gadget either...) I created this device from scratch, simply bought the components, blank circuit board and not to forget soldering iron from the local store. It now seems to work, so I'm quite proud...  

Question: I tried it before puting it in the metal box. Adjusted the pot-meter so that the sound was barely there. As soon as I start to move the antenna the sound goes crazy. Is this because it's not in the metal case or does this mean my entire appartment is bugged  ? I tried to 'detect' the signal from my cell-phone, but when I move the phone (while calling some number) towards the antenna, the sound from the speaker becomes less...

Can anyone help me out??

[maximus]

Hi

I am intersted in your rf sniffer project. several questions

1 would you be able to make it tunable so that you can select a required frequency.

2 Does the sniffer pick up normal am reciver signals

3 could you incorporate a data slicer at the output stage so data could be fed into a PC

[audioguru]

Hi Jason,
Welcome to our forum.
The project is just a simple circuit that detects a transmitter by making a tone. When you touch its antenna then you also become its antenna and it picks up more radio and TV stations, taxi cab radios etc.

When you move your transmitting cell-phone closer to it, the pitch of the tone should increase, unless you have its sensitivity control set too high and it is overloaded.

Hi Maximus,
Welcome to our forum.
1) You could tune it by replacing its R7 with a high-Q parallel LC network.
2) It picks up any RF within its frequency range and sensitivity. If you added tuning and it received a radio station, you wouldn't hear the program, just a tone.
3) Its output stage just provides a tone, no data.

[maximus]

would it be possible so that you can here what was been recieved instead of hearing audio tone.

[audioguru]

Hi Maximus,
You need a radio circuit with many tuned circuits, transistors and ICs, not this simple untuned single transistor detector circuit.

[steven]

  i think talking electretronics has the rf sniffer project or circuit. hey i just found out that my amplified ear circuit  i biult from circuit off the net has sniffed out a radio or tv reception and i can hear them talking about the tsanami disaster

[jason]

Hello Audioguru,

Thanks so far for the help. I have almost completed the construction of the gadget. Now that the circuit board is in the metal box, I don't have the problem I had before, that the thing reacted to every movement. I can now adjust the pot-meter so the tone is reduced to a mere cracking sound. However when I move my cell phone towards the antenna the pitch does not change at all. Do you have any idea what could be wrong. I fear that if a potent transmitter such as a cell phone is not detected, it will be an illusion to sniff out the real bugs.

Do I understand it correctly that the ground (-) of the circuit should be connected to the metal casing??

I attached a pic of what it looks like so far...

Hopefully you can help me out before I close the case.


 

[audioguru]

Hi Jason,
Maybe the VCO isn't working properly and doesn't change the pitch of the tone with changes in signal strength.
Maybe your cell phone operates at a radio frequency higher than this project can detect.
Try driving it closer and closer to a radio or TV transmitter with its sensitivity turned way down, to see (hear?) if it works.

It is good that your metal box made it more stable. You are correct, the circuit's ground (-) connects to the box.