[time-nuts] Opinion Of Attached - Possible HPSDR GPSDO 'Engine'

John Westmoreland john at westmorelandengineering.com
Sun Apr 15 01:36:37 EDT 2012

Hello Ed,

Wow - what a great reply and thanks for your analysis.  I am cc'ing the
HPSDR discussion group in this reply.

Well, I think the answer I am seeing for what we are trying to accomplish
is 'good enough'.

One of my friends that I consider to be one of the best engineers that I
have worked with says, 'good enough is perfect'.


On Sat, Apr 14, 2012 at 10:18 PM, Ed Palmer <ed_palmer at sasktel.net> wrote:

> 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.
> Here are some measurements that I made on the 1 PPS of the GPSTCXO and
> other GPSDOs:
> GPSTCXO .... Std. Dev. < 400 ps. min-max range < 4 ns.
> Tbolt ................ < 500 ps. ............. ~ 4 ns.
> Z3801A ............... < 300 ps. ............. ~ 2 ns.
> Z3817A ............... < 100 ps. ............. < 1 ns.
> 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.
> 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.
> A few random points to remember about the GPSTCXO:
> - There's no way to set the time zone offset - fixed at UTC.
> - There's no way to set the elevation mask - fixed at 10 degrees.
> - The Allen Deviation matched the graph in the manual which is available
> at the Jackson Labs site.
> - On the evaluation board, the 1 PPS is wired to the "DCD lead" on the
> USB-emulated serial port.
> - I can confirm that, as mentioned in the manual, performance improves
> substantially when you shield the unit from temperature fluctuations.
> - 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.
> 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.
> I have no relationship to Jackson Labs.  They did make a GPSTCXO available
> to me for this testing.
> Ed
> On 4/14/2012 7:10 PM, John Westmoreland wrote:
>> Hello Fellow Time-Nuts,
>> I am new to the group - and was asked by someone from HPSDR/TAPR to get an
>> opinion, good/bad, of the attached PDF which I hope doesn't exceed the
>> allowable byte size of posts.
>> Jackson Labs has given me a verbal on the attached as sub $300.00 QTY 1.
>>  We are seeing if there is interest in a possible 'bulk' buy.
>> I will post more on the HPSDR Wiki as soon as I sort out my password - and
>> will post an e-mail regarding the other files associated with the GPSTCXO.
>> If there is sufficient interest we may do a spin of the HPSDR Excalibur
>> project or perhaps just do a new project with the attached device.  It
>> should be easy to interface
>> directly to the Alex Bus in the OpenHPSDR Architecture.
>> Thanks and 73's,
>> John W.
>> San Jose, CA
>> AJ6BC (Ham Call Sign)
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