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

[Ed Palmer]

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)
>