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
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
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....
make me any sense...
Post subject: Posted: Thu Feb 08, 2007
Circuits & Components Forum
Joined: Tue Dec 26, 2006 5:39 pm
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
I'd bet that the 4-terminal block is a SAW-stabilized oscillator.
That might give you something to Google on.