Re: [Discuss-gnuradio] dual coherent channel rtl_sdr

[Heath Hunnicutt]

I wonder, since you are emulating the crystal output, if the R820T would ordinarily drive the crystal to rail-to-rail, square wave output.  It might be worthwhile using a high impedence probe to see what the signal you are replacing looks like.

I say this because the elonics patent suggests that staying in the linear region of the amplifiers in the feedback circuit (not rail to rail) reduces jitter.

On Thu, Sep 26, 2013 at 3:41 PM, Marcus D. Leech <address@hidden> wrote:

On 09/26/2013 06:32 PM, Heath Hunnicutt wrote:

Juha,

Ordinarily, I would choose to feed a clock into xtal_in, this seems logical.
However check out the Elonics patent:

http://www.uspto.gov/web/patents/patog/week49/OG/html/1385-1/US08324978-20121204.html

The main thing to note is that square-wave clock input should be fed to
xtal_in for the elonics chip.

If you read that patent, it may give you some ideas about feeding a clock to
xtal_in of other chips.  Maybe other chips will also expect a sawtooth in
the linear region of voltage swing, not rail-to-rail square wave.  Note the
comments in that patent on jitter at square wave, etc.,

Nobody on this thread has stated whether they are using e4000 or r820.  That
would probably be helpful.




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Well, my tests have been with R820T, which has a clock output that goes to the RTL2832U chip.

I've actually tried both sides of Xtal_I and Xtal_O on the R820T, and it makes no difference.


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

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