hi Herbert

I have the same kit , how can I assist you?
mine works fine.
did you double check the assembled kit ? all parts in place ? what about the
voltage supply? did you know there is two supplies?
6V and 12V ...

Regards

Tal Bejerano
AMC - ISRAEL


-----Original Message-----
From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On
Behalf Of Herbert Graf
Sent: Sunday, June 09, 2002 1:52 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: [EE]: FM transmitter problems


Hello to all, was wondering if someone might be able to helping me figure
out what wrong with the FM transmitter I have. First a little background...
:)

I built an MP3 player out of a Pentium PC and installed it in the car. I
currently have an audio line going to the front which I connect to a tape
adapter, the car radio has no audio in, and I don't want to modify it. This
system works, but is a little involved.

So, I had the "brilliant" idea of using an FM band transmitter instead. I
tried a few retail cheapies (read RadioShack) and none worked well, the
radio catches the signal but gets louder, and softer, then louder again, at
a freq of about 0.5Hz.

I decided I'd buy a cheap kit and build my own Stereo FM transmitter, I
decided on the CK222 by CanaKit (www.canakit.com). It is a simple stereo
transmitter based on the BA1404 with a single transistor acting as a power
amp. I assembled it and got it work, however it exibits the EXACT same
problem, the radio signal comes through but it alternates between really
quite and loud, and about 0.5Hz. I am truly at a loss as to WHY this is
occuring, I also tried my home theatre receiver, with the same results!@ :(

I connected my trustly HP 1710A scope to it (a 100MHz analog dual trace
beauty from the 70's!) and I don't quite understand the waveforms fully
(both are DC coupled, 0.1V/div). I made links to them here:

http://repatch.dyndns.org:82/06080001.jpg (20ns/div) 84k
http://repatch.dyndns.org:82/06080002.jpg (50ns/div) 109k

There are TWO signals, one at just below 50MHz (which doesn't seem to
modulate at all) and one at something less (which DOES seem to modulate),
the interesting thing is the lower freq signal doesn't change much if I
change timebase, which tells me there are some harmonics or something
happening since I'm at the edge of the scopes input bandwidth. I had the
transmitter set at 88.6 MHz.

If anybody has any ideas as to what might be causing this I'd love to know,
I have little RF experience (hence the buying of a retail product at first,
and then a kit) but would love to figure this out. Could it be the AFC
circuit in the digital tuners "hunting" for the not so perfect stereo
signal? I say this since if I short out the crystal on the board (thereby
removing the FM stereo pilot signal at 19kHz (I think) and causing the
receiver to go into mono mode) the problem magically disappears. Thanks in
advance for any help/advice. TTYL

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