Re: [Discuss-gnuradio] Testing crystal accuracy

[Jason Matusiak]

Marcus,
 
> I shouldn't have hit the send button yesterday and went to bed right after.
> Had a night of bad sleep; I realized my formulas only applied to the case of 
> real valued signals.
Sorry for causing your consternation last night!

> Your dongles won't be giving you cosines in complex baseband for a signal 
> they see at;
> they will give you complex sinusoids
> and , respectively.
> To be complete, there'd also be a phase offset, so it'd be , and .
That makes sense and is something I should have probably realized on my
own as well :(.
 
> Now, multiplication of these really just is addition of the exponents, so 
> 
> which means you'll only see the "sum frequency".
> That's why you'd use the "multiply conjugate" block instead:

OK, so bring in the signals, do a Multiple Conjugate, LPF, and then sink
it.  Got it. 
 
Is the transition width of the LPF going to be crucial (ie: do I need to
have it be a multiple of something)?

I attached the script screenshot I generated and the results, I think I
must still be interrupting something wrong as I don't see how I can best
compare the two crystals.  Sorry I am not 100% there, but I think I am
close.

CrystalTest.grc.png
Description: PNG image

Screenshot from 2016-01-13 08:12:23.png
Description: PNG image