Debugging a Bug - Crystal Controlled - Have You Met One? - RF
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 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
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.