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