Thank you for visiting RF Cafe! Electronics World Cover,TOC,and list of posted Popular Electronics articles QST Radio & TV News Radio-Craft Radio-Electronics Short Wave Craft Wireless World About RF Cafe RF Cafe Homepage RF Cafe in Morse Code Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs Twitter LinkedIn Crosswords Engineering Humor Kirt's Cogitations Engineering Event Calendar RF Engineering Quizzes AN/MPN-14 Radar 5CCG Notable Quotes App Notes Calculators Education Magazines Software,T-Shirts,Coffee Mugs Articles - submitted by RF Cafe visitors Simulators Technical Writings RF Cafe Archives Test Notes Wireless System Designer RF Stencils for Visio Shapes for Word Search RF Cafe Sitemap Advertising Facebook RF Cafe Forums RF Cafe Homepage Thank you for visiting RF Cafe!

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

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

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
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...



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


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 ?


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


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

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

Good luck!

Posted  11/12/2012

RF Cafe Software

   Wireless System Designer - RF Cafe
Wireless System Designer

RF & EE Symbols Word
RF Stencils for Visio
Calculator Workbook
RF Workbench
Smith Chartâ„¢ for Visio
Smith Chartâ„¢ for Excel

About RF Cafe

Kirt Blattenberger - RF Cafe WebmasterCopyright
1996 - 2022
Kirt Blattenberger,

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website:

Try Using SEARCH
to Find What You Need. 
There are 1,000s of Pages Indexed on RF Cafe !