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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