[USRP-users] Non-desired received frequency components when decreasing decimation

Jorge Miguel jmiggal at gmail.com
Mon Nov 29 03:01:37 EST 2010


Hello all,

I am receiving a single tone at (5GHz + 10KHz) with a USRP2 and the XCVR2450
tuned at 5GHz.

The reception of the tone is correct. However, as long as I decrease the
decimation of the USRP2 I start receiving very strong components at
frequencies that depend on the USRP decimation. See pictures bellow:

10 KHz at 512 decimation:
http://s2.subirimagenes.com/otros/previo/thump_557687610khz512dec.jpg

 10 KHz at 64 decimation:
http://s2.subirimagenes.com/otros/previo/thump_557687710khz64dec.jpg
Signals at +- 500KHZ ?

 10 KHz at 32 decimation:
http://img560.imageshack.us/img560/6688/10khz32dec.jpg
Signals at +- 500KHz and +- 1500KHz?

When I change the frequency of the input tone, those non desired components
also move the same frequency amount that the input tone. But they are not
part of the input signal (single tone from a good signal generator).
Furthermore the input frequency is smaller than Fs/2.

What is going on? Any ideas?

Many thanks,
Jorge.
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