[Discuss-gnuradio] Spectrum at 1 GHz

[Umair Naeem]

I have a query regarding flow graph in GRC.
I am trying to get spectrum from DBS_RX daughter board using GRC. I have used 
three blocks as

USRP2 Source --> FFT Filter --> FFT Sink

They have following parameters,

USRP2 Source:
Decimation 1M
Frequency 1G
Gain (dB) 0

FFT Filter:
Decimation 1
Taps firdes.complex_band_pass(1.0, 3000, -0.05e3, 0.05e3, 5, 
firdes.WIN_HAMMING, 0)

FFT Sink:
Sample Rate 2K
Baseband Frequency 1K
FFT Size 512
Refresh Rate 30


I need to display shows frequency spectrum centered at 1 GHz. Since I am using 
decimation of 1M, the frequency is lowered down to 1K. I filter it using FFT 
bandpass filter with 100 Hz bandwidth. The fft sink shows spectrum at around 1 
KHz. The problem is if I do not use decimation, the GRC seems to be very slow 
(may be processing 1 GHz at  GHz sample rate is too much). I need to make a FFT 
plot showing spectrum at 1 GHz. How Can I accomplish this?


Regards,
Umair Naeem
MSc Communication Engineering
Chalmers University ot Technology, Sweden.