[Discuss-gnuradio] BasicRX boards and AM transmission

[Martin Braun]

Hi,

I'm still in the exploring phase of my GNU radio work and currently ran into 
an annoying problem. All I want to do is transmit AM from one USRP to 
another, which I thought would be the simplest RX/TX chain I could come up 
with for a start.

However, I have not managed to get a clean AM reception with a USRP. I'm 
pretty sure the tx component works, because I can listen to my transmission 
with an old kitchen radio and it sounds fine.

RXing with the USRP simply doesn't work, though, neither with usrp_rx_nogui.py 
nor with anything I could come up with. I get lots more noise than expected 
and usually I get a very loud buzz or whistle which is a lot louder than the 
TXed signal. Has anyone else had this problem?

I'm using the Basic* boards directly connected to an antenna (no bandpass 
filtering). I realize this is not how the BasicRX is intended to be used, but 
can this be the cause of a loud buzz or would it only create lots of extra 
noise? Basically, is this a completely futile attempt?

I also tried the TVRX and then I sometimes get some spectral lines around 
40kHz next to my main signal (this frequency doesn't occur anywhere in my RX 
chain, it's audio at 32kS/s interpolated to 320kS/s for the USRP). My filters 
on the TX chain seem OK, at least I haven't seen those spectral lines on an 
(external) spectrum analyzer. Has anyone else ever seen lines like this?

Thanks for any help,
-- 
Martin Braun
Institut fuer Nachrichtentechnik
Universitaet Karlsruhe

http://www.int.uni-karlsruhe.de