Re: [Discuss-gnuradio] problems with benchmark_ofdm and N210

[Marcus D. Leech]

> On Wed, Jun 8, 2011 at 11:24 PM, Morgan Redfield<address@hidden>  wrote:
> I found that centering my FFT on a frequency that's offset from what
> I'm transmitting at will remove that central spike. I was able to
> finally see the gap in the center of the OFDM boxcar and adjust that.
> It looks like in my setup I have an offset of about 6kHz.
>
> My OFDM signal never seems to be more than about 10 dB above the noise
> floor though. When I bump up the gain or tx-amplitude, everything gets
> raised by the same amount. I'm still not able to demodulate packets,
> and I think this is why. Do you have any advice about this?
>
> Thanks,
> Morgan
If changing the *TX* amplitude doesn't improve things, then perhaps the 
frequency offset is the problem.
  I'm not much of an OFDM guy, but it seems to me if your OFDM "bins" 
aren't where they're supposed to be,
  to less than a fraction of a bin-width, then there could be problems.

Also, to confirm that your RX is sensitive enough, if there's a way you 
could generate a single-tone signal at
  about -110dBm, directly connected to the RX, and see if you can see 
the tone in an FFT display.  If not then
  you have RX sensitivity issues.




--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org