RE: [Discuss-gnuradio] Spectrum at 1 GHz

[Ian Holland]

Hi Umair

I believe the decimation factor you have chosen is beyond the maximum
allowed (I think, from memory this is 512, which is well less than 1M =
1 times 10^6).

It seems you are trying to sample the passband signal to show a spectrum
at 1 GHz, however a digital-down conversion is performed at the
receiver, so you should see a signal at baseband. You should not need to
use such a high sampling rate - ideally, Nyquist rate (based on the
signal bandwidth when downconveted to baseband) will suffice.

Regards

Ian.
 


-----Original Message-----
From: address@hidden
[mailto:address@hidden On
Behalf Of Umair Naeem
Sent: Monday, 12 April 2010 4:59 PM
To: address@hidden
Subject: [Discuss-gnuradio] Spectrum at 1 GHz

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.


_______________________________________________
Discuss-gnuradio mailing list
address@hidden
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio