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Debugging a bug - crystal controlled - have you met one? - RF Cafe Forums

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Post subject: Debugging a bug - crystal controlled - have you met one? Posted: Mon Feb 05, 2007 6:45 pm


Joined: Sun Apr 30, 2006 2:22 am
Posts: 1
I have several UHF "bugs" and I wish to understand several things:
All the bugs I have work on the 433MHz band. SMD components.
Several use a simple metallic case crystal, U49, and several use SMD, and I suppose they work on the third overtone and then doubled, meaning I think the crystals are around 87MHz. The SMD ones have 4 "legs" - no idea which kind of crystal is this one, or it may be even an oscillator. I cannot debug it to know which kind of device is it. I need your help, maybe someone may know this device: 4 legs - one from each side, black, about 6mmx4mm. All I could do is to measure the frequency with a counter - at 3 legs it shows me 433.9MHz - but I'm not 100% sure it's not inductance from the PCB. I'll be very thankful for any help - maybe a link to similar device.
It confuses me very much, as it is written 480 - no doubt, but it works on 433.9MHz - so it has no sense. As it uses only 3 transistors and 1 diode - which I guess it's a varicap (maibe a PIN diode), it's a "miracle"... 2 AF transistors and one (the one which you can see at the end of the PCB - and it's "deleted" or in any way I cannot read what is written on it) - I suppose it's an RF amp....
It doesn't make me any sense...



Post subject: Posted: Thu Feb 08, 2007 10:50 am


Circuits & Components Forum 13

Joined: Tue Dec 26, 2006 5:39 pm
Posts: 10
That circuit is quite simple. If you would provide us with a schematic, I am sure that some reader could tell you everything you need to know.

Are finding these transmitters in actual service? I mean have you found them in someone's office or laboratory ? If so, I would be investigating the laws concerning industrial espionage in your locale.

Does this unit operate FM or AM ?


Post subject: BugPosted: Thu Feb 08, 2007 1:24 pm


Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104

I'd bet that the 4-terminal block is a SAW-stabilized oscillator. That might give you something to Google on.

Good luck!

Posted  11/12/2012
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