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
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.
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
Components Forum 13
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.
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.