Hello Ed,<div><br></div><div>Wow - what a great reply and thanks for your analysis. I am cc'ing the HPSDR discussion group in this reply.</div><div><br></div><div>Well, I think the answer I am seeing for what we are trying to accomplish is 'good enough'. </div>
<div><br></div><div>One of my friends that I consider to be one of the best engineers that I have worked with says, 'good enough is perfect'.</div><div><br></div><div>73's,</div><div>John</div><div>AJ6BC<br><br>
<div class="gmail_quote">On Sat, Apr 14, 2012 at 10:18 PM, Ed Palmer <span dir="ltr"><<a href="mailto:ed_palmer@sasktel.net">ed_palmer@sasktel.net</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I recently had a chance to look at the GPSTCXO. I was quite impressed. It's performance is a lot better than any bare GPS receiver, but maybe not as good as some GPSDOs.<br>
<br>
Here are some measurements that I made on the 1 PPS of the GPSTCXO and other GPSDOs:<br>
<br>
GPSTCXO .... Std. Dev. < 400 ps. min-max range < 4 ns.<br>
Tbolt ................ < 500 ps. ............. ~ 4 ns.<br>
Z3801A ............... < 300 ps. ............. ~ 2 ns.<br>
Z3817A ............... < 100 ps. ............. < 1 ns.<br>
<br>
These measurements were 1000 pulses or more measured with an HP 5372A or 5370B for the Z3817A. The Z3817A requires an external 1 PPS source to lock to. I used a Navsync CW12-wi. Over longer periods of time typical GPS wander is present in all units.<br>
<br>
I measured the 10 MHz output of the GPSTCXO with the Histogram Time Interval function of my 5372A. Out of 200 million cycles, every one had a period of either 100.0 or 100.2 ns. There wasn't even one outlier. I have OCXOs that aren't nearly that good.<br>
<br>
A few random points to remember about the GPSTCXO:<br>
- There's no way to set the time zone offset - fixed at UTC.<br>
- There's no way to set the elevation mask - fixed at 10 degrees.<br>
- The Allen Deviation matched the graph in the manual which is available at the Jackson Labs site.<br>
- On the evaluation board, the 1 PPS is wired to the "DCD lead" on the USB-emulated serial port.<br>
- I can confirm that, as mentioned in the manual, performance improves substantially when you shield the unit from temperature fluctuations.<br>
- If you use Z38XX to communicate with the GPSTCXO be sure to disable serial echo as described in the manual. The GPSTCXO _really_ doesn't like serial echo. It can cause the unit to reboot.<br>
<br>
The GPSTCXO stands between a bare GPS timing receiver and a typical GPSDO. It's performance is closer to a GPSDO than to a GPS receiver, but it's price is closer to the bare receiver than to the price of a new GPSDO. It should be useful in many situations.<br>
<br>
I have no relationship to Jackson Labs. They did make a GPSTCXO available to me for this testing.<br>
<br>
Ed<div><div class="h5"><br>
<br>
<br>
On 4/14/2012 7:10 PM, John Westmoreland wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hello Fellow Time-Nuts,<br>
<br>
I am new to the group - and was asked by someone from HPSDR/TAPR to get an<br>
opinion, good/bad, of the attached PDF which I hope doesn't exceed the<br>
allowable byte size of posts.<br>
<br>
Jackson Labs has given me a verbal on the attached as sub $300.00 QTY 1.<br>
We are seeing if there is interest in a possible 'bulk' buy.<br>
<br>
I will post more on the HPSDR Wiki as soon as I sort out my password - and<br>
will post an e-mail regarding the other files associated with the GPSTCXO.<br>
<br>
If there is sufficient interest we may do a spin of the HPSDR Excalibur<br>
project or perhaps just do a new project with the attached device. It<br>
should be easy to interface<br>
directly to the Alex Bus in the OpenHPSDR Architecture.<br>
<br>
Thanks and 73's,<br>
John W.<br>
San Jose, CA<br>
AJ6BC (Ham Call Sign)<br>
<br>
</blockquote>
<br></div></div>
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