Capture the same reference tone at
with both dongles, tuned to 
, choose 
.You would see a baseband tone at
and 
, respectively, and since no two
oscillators are identical, 
.W.l.o.g., let
be the tone as seen by your
"improved" dongle.Multiply both signals; what should happen is intermodulation; use a low-pass filter with a cutoff of ca
, so that you just get the
difference frequency at 
.Qt frequency sink, or quadrature demod->Qt time sink.
Cheers,
Marcus
On 12.01.2016 18:43, Jason Matusiak
wrote:
Thanks for the quick response Marcus!!!! Since my Latex isn't very good (as in pretty much non-existent). Let me see if I can rewrite what you recommended in my dumbed down language and see if I am close.: *I have two dongles, dongle 1 will be my modified dongle, dongle 2 will be my un-modified dongle. *Put a a known reference tone into each of the dongles where Ftune = Fref - Foffset ** Foffset should be roughly a third of the sample rate **An example at a sample rate of 1.024Msps would be a reference tone at 98MHz, and then tune the dongles to 97.659MHz *I'll now see a baseband signal for both dongles whose offsets won't be exactly the same. *Multiple the resulting signals found above against each other (offset,1 * offset,2) *Pass that through a LPF with a cutoff of Fsample/4, or 256khZ in this case **This will give the difference between the frequencies at frequency at Foffset,1 +/- Foffset,2 *perform a QT freq sync or a quad demod into a QT time sink to compare. Is that close? I think I am missing something in there, and I have a feeling that it has to do with the multiplication step as that makes the least amount of sense to me. Any way to enlighten me on what I am missing above? Thanks!