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

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


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

Lieutenant

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...

Regards,
Ridgh






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wb9jtk
Post subject: Posted: Thu Feb 08, 2007 10:50 am

Captain


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 ?


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fred47
Post subject: BugPosted: Thu Feb 08, 2007 1:24 pm

General


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

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

Good luck!
Fred



Posted  11/12/2012
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