[time-nuts] Rb vs.Crystal OCXO
Tom Van Baak
tvb at LeapSecond.com
Sun Apr 27 18:25:17 EDT 2014
> I unplug the antenna from my fury boards. I hope this is an effective alternative.
That's probably what I did for my tests. Or maybe I just used a SCPI command to do it. I don't remember anymore. Sometimes when I test multiple GPSDO at once it's convenient to just remove the antenna coax from the splitter; leaving everything else in the lab untouched. That method is also nice since you can see in parallel how quickly or slowly each GPSDO reacts to LOS. Then there's the John Miles' method: a hp RF relay to remotely connect/disconnect the antenna line on demand.
In the plot I made many years ago (http://leapsecond.com/pages/gpsdo/) you can see the Fury has very similar short-term performance with and without the antenna. So perhaps you have less to worry about on that GPSDO. Again, a lot of it depends on the tuning parameters (user adjustable), and your antenna/reception, and your lab environment, so I wouldn't want to make too many generalizations based on make/model alone.
Even "identical" GPSDO can show significant differences. My plots are for my Fury. It's hard to know how close your Fury performs to mine. See also section 6, Fury vs. Z8301A (http://leapsecond.com/pages/fury/) for another comparison.
----- Original Message -----
From: "Bill Dailey" <docdailey at gmail.com>
To: "Tom Van Baak" <tvb at leapsecond.com>; "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Sunday, April 27, 2014 10:04 AM
Subject: Re: [time-nuts] Rb vs.Crystal OCXO
Sent from mobile
On Apr 27, 2014, at 9:02 AM, "Tom Van Baak" <tvb at LeapSecond.com> wrote:
>> The Pendulum GPS-88 and GPS-89 have a button on the front you push when
>> you want to force it into hold-over to do your measurement, for this
>> very reason.
>> PPS steering and OCXO steering is the same thing once you forced the PPS
>> into the right range. Some *really* depend on the synchronicity between
>> 10 MHz and PPS, and you should not obscure it if possible.
> When doing a sensitive measurement where stability is more important than accuracy I turn off GPS disciplining.
> The TBolt has commands to go into and out of holdover. But more effective are the 0x8E,0xA3,4 and 0x8E,0xA3,5 commands which simply disable and enable disciplining.
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