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From: | Marcus Müller |
Subject: | Re: [Discuss-gnuradio] Testing crystal accuracy |
Date: | Tue, 12 Jan 2016 18:47:28 +0100 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0 |
Oh, sorry, I forgot to hit the "replace LaTeX by rendered formulas";
let me re-do that, before I comment on your comments :) 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! |
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