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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Neil,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Locking to 10K PPS does not provide all the benefits you would expect
because of the statistics of the 10K PPS signal. That fact killed a “black
project” that Tom and I worked on a while ago. Locking to 1PPS is not
more difficult than locking to the 10K PPS and the Jupiter is an old design.
There are new receivers on the horizon that will all be 1PPS. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Yes, the best locking solutions (including mine) are proprietary, but
we may be able to get past that with some thought or policy flexibility. We should
decide what oscillator (and clock) characteristics are important and design to
meet them. I have some ideas that I will share later.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Rick<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>W2GPS<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>AMSAT LM2232<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> </span><o:p></o:p></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> hpsdr-bounces@hpsdr.org
[mailto:hpsdr-bounces@hpsdr.org] <b><span style='font-weight:bold'>On Behalf Of
</span></b>neil whiting<br>
<b><span style='font-weight:bold'>Sent:</span></b> Thursday, May 25, 2006 6:18
AM<br>
<b><span style='font-weight:bold'>To:</span></b> hpsdr@hpsdr.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> [hpsdr] High Accuracy
Timing for HPSDR</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>A few thoughts on SDR frequency references. I'm not sure the Gibralter
PCB <br>
needs to be as complex as suggested. <br>
<br>
- Most people who are worried about having GPS-accurate frequency are likely <br>
to have an existing reference source. <br>
<br>
- Many of those who don't have an existing reference are likely to be happy <br>
with a simple OCXO tweaked to the right frequency. Locking to GPS is not
<br>
necessary for SDR operation. <br>
<br>
- If a locked frequency is required (eg for modern digital modes, <br>
microwave EME, etc) <br>
- locking to 1pps is tricky/complex and existing solutions may not be <br>
open source <br>
- locking to 10kHz as output by some GPS modules (eg. the Jupiter-T, <br>
which is available surplus) is rather easier, just using a
simple PLL <br>
<br>
It would seem that a good balance would be to provide 3 options: <br>
- an external reference input, <br>
- an option to use the Gibraltar PCB populated with just an OXCO, no locking <br>
- use Gibraltar with simple PLL locking to 10kHz from a suitable onboard GPS <br>
module <br>
<br>
Does this make sense? Have I missed something? <br>
Are suitable GPS modules available at a reasonable price (new, not surplus)? <br>
<br>
73, Neil G4BRK <o:p></o:p></span></font></p>
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