Electronic Eavesdropping Devices Detector

[badai]

Is it alright if I don't install into the metal box?....... :-\

Do you have any circuit that can detect the signals up to 108MHz(approximately-like tune radio frequency for FM)

 

[audioguru2]

Hi Badai,
I don't think a metal box is necessary for this project because it doesn't have much RF gain.
Lots of circuits can detect signals up to 108MHz and higher, they are called radios and TVs.

 

[badai]

actually i'm a beginner user for EAGLE Layout Editor, so I'm not sure either i draw the layout right or not. Can you send me the pcb design(electronic eavesdropping devices detector), so i can send directly the transparent directly to pcb lab at my faculty?

 

[audioguru2]

Hi Badai,
A picture of a bare PCB and its parts layout is in the article for the project.

 

[HoLoDuKE_za]

Hi everybody, I'm new to this forum.

I built the rf sniffer circuit only to find that it didnt work - the schematic doesnt match the actual PCB layout at all. Take a second glance! When I built the circuit according to the PCB layout, including enclosing it in a metal box, I found that it was just sounding continuously... It only responded to my cellphone while I was making a call, and when it was held within inches from the device. Any clues as to what problems I may have encountered?

 

[audioguru2]

Hi Duke,
Welcome to our forum.
I am sorry to hear that the project didn't work for you.
Please tell us what errors you found on its pcb layout.
1) Did you substitute any parts?
2) When you turn down the sensistivity control, dose the pitch of the VCO reduce to a low-pitch growl or stop?
3) Do you have a strong radio or TV transmitter nearby ?

 

[HoLoDuKE_za]

I should've been more clear about what I said earlier.

- I built the project according to the schematic and not the PCB.
- Afterwards, I realized that the schematic and the PCB on this website don't correspond.
- I then changed the project to correspond to the PCB layout.

In response to audioguru's questions:

1) I used an LM324, 14-pin IC as a substitute, instead of the "IC1 = 

 

[audioguru2]

Hi Duke,
Your LM324 should work fine in this circuit.

I see what you mean that the schematic and the PCB in this project don't correspond.
I think both the schematic and pcb are wrong and the circuit will work well if you re-build it to agree with the VCO on the LM324 datasheet:

View attachment 36888

 

[HoLoDuKE_za]

Hi audioguru and all o' ya...

I think that the mistake I made initially was to assume that the schematic is incorrect and not the PCB.

I built the whole project *on breadboard*, according to the schematic. I would suppose that this is why it wouldn't work. When dealing with such high frequencies such as 1MHz-1GHz, breadboard testing won't work...

Fore sure, I know that there is an error on the schematic (D1 is used to label a capacitor) but I dont know whether the schematic was indeed the right one for this project.

The strange thing is that when I checked the schematic on the 'Smartkit' website, I found the very same schematic for Kit #1154.

Think I'll try a new approach and let you all know my results.
Thanks again..

The Duke,
South Africa

 

[audioguru2]

Hi Duke,
Sometimes kit-makers put errors on purpose on their schematics and pcb patterns to stop people from simply copying them. It is fun for me to try to re-engineer what is correct.
Besides the opamp wiring and parts differences, all around the diode looks odd.

The RF section of this project belongs on a tightly layed-out pcb to work at those extremely high frequencies. It hardly has any RF gain, maybe to avoid picking-up radio and TV stations, so I don't expect it to be very sensitive.  ;D

 

[Olihou]

Hi Audioguru and every body

I am curious at the thinking that kit-makers put errors in their products purposely -- and if the kits would not work -- would that defeat their intention to sell the kits  -- so they have protected their intellectual properties -- but not their businesses ?

I have experience in using kits only a few times and am lucky that I succeed every time. It is nice to have some one in this forum poiting out the traps, saving the headache of many .....

 

[audioguru2]

Hi Olihou,
I don't think the kits have errors, only the schematic and/or the pcb pattern so that circuits and pcb's copied from them don't work, but the kits work fine.  ;D

 

[Olihou]

I see.

Thanks a lot Audioguru !

 

[maroela]

i have purchased the electronic eavesdropping devices detector kit, assembled it, but it doesnt work. I checked if all the components were in the right place, and it seemed all to be in order. Could there be a problem with the kit, or is there something I could have done wrong?

 

[audioguru2]

Hi Maroela,
Welcome to our forum. ;D
Does the speaker make a sound when you turn-up the sensitivity?
What radio transmission are you trying to detect?
Please measure the voltages at the outputs of the opamps and the collector of  TR1 and post them here.

 

[maroela]

the speaker makes no sound at all, no matter what I do to the sensitivity. I am just trying to detect a normal FM bug. Its going to be part of a university project. my multimeter broke a few days ago, so i will not be able to give you those readings. As this is quite urgent ( it needs to work by tomorrow!), please could you give me any advice that might work.

 

[audioguru2]

Hi Maroela,
Maybe the circuit isn't sensitive enough to detect the low power of an FM bug.
Try to detect a cell phone.

Maybe the kitmaker supplied 2N2222 transistors with a plastic case. To be certain that you have installed them correctly, compare the pins of the metal case on the kit's layout diagram with this comparison picture showing both:

View attachment 37036

 

[audioguru2]

I have corrected the schematic for the Electronic Eavesdropping Devices Detector project so that it is the same as the project's pcb and parts layout diagram, and is also the same as National Semiconductor's schematic:

View attachment 37037

 

[maroela]

hey audioguru, thanks for all your help, i played around with the circuit for a while, and im not sure exactly how i did it, but i eventually got it to work. Ill probably speak to you again on another forum,  cheers!

 

[audioguru2]

You're welcome, Mareola. ;D
Its great to hear that you got it to work.