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Re: [Discuss-gnuradio] Passive radar using my hacked dual coherent chann


From: Juha Vierinen
Subject: Re: [Discuss-gnuradio] Passive radar using my hacked dual coherent channel rtl_sdr dongle
Date: Fri, 27 Sep 2013 15:48:27 -0400

Cool. 

I wrote up a few blog posts about the tests I did this week:

http://kaira.sgo.fi/2013/09/16-dual-channel-coherent-digital.html
http://kaira.sgo.fi/2013/09/passive-radar-with-16-dual-coherent.html

PS. I tried adding a third dongle to run with the same master clock. I didn't do it correctly this time either by using an active signal splitter, as that would increase the total cost :). I'll hopefully have some more to report next week. 

juha


On Fri, Sep 27, 2013 at 2:16 PM, Marcus D. Leech <address@hidden> wrote:
On 09/26/2013 11:27 PM, Jared Clements wrote:

Since they're clocked together I would assume that your alignment would consist of interpolation on the primary FM signal, what do you do to remove it later?  If your code is too messy to release can you share a block diagram?

Thanks,

Jared


I just re-did my tests with a pair of synched dongles, and instead of inject RF externally, I just tuned it close to the 2nd harmonic of the
  clock.

That produced quite stable, near-perfect, correlation, once I adjusted the phase to peak up the correlator output.  This puzzles me greatly.

This implies that both dongles are properly phase-locked to the master clock, and that the leakage  is being coherently downconverted, and
  that no samples are being dropped.

So, my phase-coherence issues are with my external RF injection.  Which I just plain don't understand....


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



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