[Discuss-gnuradio] Amplitude variations inn FFT sink

[eivim]

Hi all

I'm trying to use the USRP1 as a beacon receiver i.e. measure the  
amplitude and frequency of a signal then store the detected values to  
file. I'm using the DBSRX daughter board to measure satellite beacons.

However I have ran into some problems. When viewing the FFT plot from  
USRP_FFT.py I can see amplitude variations of up to several dB when  
using a highly stable frequency generator. The amplitude variations  
seem to increase with decreasing input power i.e lower C/N. Even with  
the averaging function turned on the fluctuations are noticeable at  
about 10 dB C/N.

My question is therefore: What is causing this ? And is there a way to  
avoid or reduce this effect ?

I have already tried to reduce bin size an added FIR filter to the USRP_FFT.

Thanks in advance.

Eivind

usrp_fft.py
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