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

[Ulrich Bangert]

Ed,

> - 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.

as the author of the mentioned Z38XX I would like to clarify this claim. If
serial echo is enabled then the GPSTCXO is the SOURCE of the serial echo and
echoes every single character sent by Z38XX. This worries Z38XX a lot
because it expects to put forward a question to the device and then to
receive an answer to that question. It does not expect to receive its own
question and for that reason it takes the echoed question as the answer
sometimes. 

The problem is the "sometimes" because the next time the correct answer may
be read. Whenever you get the impression that the communication with a GPSDO
is kind of "unstable" with Z38XX you should give the serial echo the first
check. That applies to ALL GPSDOs and not only the GPSTCXO. The GPSTCXO was
the first device to notice this fact because the default for the serial echo
seems to be "On" which is a handy feature when you use a common terminal
program for communication.

Best regards
Ulrich Bangert   

> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Ed Palmer
> Gesendet: Sonntag, 15. April 2012 07:18
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] Opinion Of Attached - Possible HPSDR 
> GPSDO 'Engine'
> 
> 
> 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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