[USRP-users] Capturing signals at the carrier

Marcus D. Leech mleech at ripnet.com
Mon Sep 30 18:18:45 EDT 2013


On 09/30/2013 04:47 PM, Cochenour, Brandon M CIV NAWCAD, 4.5.6 wrote:
> After some further experimentation...I notice that not all carrier frequencies result in the DC component being removed.
>
> For example....using the N210 with WBX...
>
> At a 50 MHz carrier...I can modulate a single tone all the way down to about 200 Hz with no issue.  Between 100-200 Hz...I observe all sorts of weird harmonics.  At 100 Hz...everything is fine.  Between 1-100 Hz...strange harmonics. And then a 0 Hz...a clear spectral peak at DC.
>
> However at certain other frequencies....I'll get no DC through at all.
>
> I also note that it doesn't matter if I use the TX side of the WBX as my input...or if I try to tune an external source to get as close to the USRP LO as I can.  Some center frequencies work.  Others don't.
>
> There doesn't seem to be much rhyme or reason as to why certain frequencies work, and others don't.  Should there be?
>
>
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The amount of DC offset and gain and IQ imbalance produced in the PLL is 
highly dependant on the tuned frequency.



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

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