[USRP-users] Capturing signals at the carrier

Cochenour, Brandon M CIV NAWCAD, 4.5.6 brandon.cochenour at navy.mil
Mon Sep 30 16:47:14 EDT 2013


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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