[time-nuts] Next upgrade
EWKehren at aol.com
EWKehren at aol.com
Thu Nov 23 13:18:35 EST 2017
The Next upgrade has touched several subjects we deal with on a dayle
basis. Allow mw to add my thoughts. First we are time nuts trying within our
limits to advance time and frequency generation and measurement with
affordable resources. We are at least a factor four orders of magnitude behind the
big boys in performance and combined available resources.
As a market we are to small potato's so products tailored to our needs are
limited and are getting less. An example SRS FS740 a nice box but no help
to get past E-12. New GPSDO's for Telecom do not have 5 or 10 MHz output.
PRS-10 a nice Rb, originally intended for FRS replacement has ADC and DCA
control limeting it to 2 E-12. I have one, have not said anything because I
want to get rid of it.
The question of why Rb. For our work there are only two reasons. Not living
next to NIST the only precise frequency reference is GPS. To overcome its
limits you need long time averaging. Aging compared to a OCXO is orders of
magnitude less. Second because of aging and tuning range a 16 bit DAC will
do the job. There was recently discussion of the use of the LTC1655 which
is still my # 1 choice. What was not mentioned on the 1650 is that in needs
a external reference discontinued and double ling the cost. 18 bits would
be nicer but we have not found one affordable. Using a modified Shera with 1
E-14 steps yields a range up to 6.4 E-10. We are presently running three
Tbolts, standard, OSA 8600 and the Efratom M100 with 40 000 seconds and 6
E-17 per uV direct C field drive through a 10 K resistor. Temperature,
pressure and some start up issues make it a less desirable option.For temperature
and pressure we have an interface board, but automatic recovery after
power or GPS loss is not there after two weeks. That is why we keep going back
to 1655/Shera. Going to 6 E-17 keeps the jumps we all see below ! E-13.
Attila recently caught up with me on my Europe trip at Juerg's home in
Switzerland and can tell you about all our projects. Using the standard Tbolt we
also showed him the consistent jumps with a Tracor 527E and a Cesium
Yes doing a Cesium GPSDO again with 1655/Shera is doable but the question
has to be: is it necessary. I worked with Richard McCorkle on it 4 years
ago. The question is does it make sense. My HP5061B with the new smaller tube
shows no aging but my GPS measuring capabilities are limited to 1 E-12. We
have decided to monitor 1 pps from a Tbolt against a 1pps derived from our
respective Cs and if necessary manually adjust.. To do it with le least
amount of equipment we decided to take a PICTIC II a divider chain and a
custom V drive using USB stick and blue tooth monitoring low cost, no fan and
low power. I never built a PICTIC but did combine Richard's and my boards for
cost reason. Bill Riley did an extensive evaluation and recommended to
consider 4 layers. This was the first time I looked at the board. Richard used
schematic capture resulting in no ground plane and long ground runs not
what you want when you chase nsec. I took a look and decided 4 layers is not
necessary but was able to add a nice ground plane. I have boards of PICTIC,
divider and V drive. Right now we still have work to do on M100/FRK GPSDO
and the high resolution Austron counter. If some one wants to build a unit,
please contact me off list, if I am convinced you will do it, I will send
you the boards free of charge.
Richard did a PICTIC III and was working on a 4 and I was working on a 5.
Sadly contact with him has stopped, the last correspondence was two years
ago, he had fallen and broken some ribs and had prostate cancer. His last
words where, he would get back with me after health was back under control. I
have tried what I did with Brooks, send a letter with USPS which resulted
in Brooks Wife responding, you know the details, no response from Fairbanks.
Has any one heard from Richard? He did a lot of work for us, brilliant, I
would ask a question, because of the time zone the typical next day
response was working PIC code.
In a message dated 11/22/2017 7:26:57 P.M. Eastern Standard Time,
k8yumdoober at gmail.com writes:
For the most part the SRS-10 is a nice choice, although I'd always be wary
of buying a
My only real beefs are that the tuning granularity is rather coarse, about
2E-12, and the
disciplining loop seems to be a bit aggressive so that the poor oscillator
around quite a bit by the GPS. This makes for rather ugly-looking plots of
The above comments are derived from about 3 years of operating one as a hot
emergency spare at the Arecibo Observatory against the day when the H-maser
crashed abruptly. In this case the SRS-10 was embedded in an FS725 which
On Wed, Nov 22, 2017 at 4:16 PM, Jerry Hancock <jerry at hanler.com> wrote:
> Three questions:
> 1) Now that I’ve split my Lucent RFTG-U into a REF0 and REF1 unit with
> both supplying 10Mhz and 1PPS, is there a way to combine the outputs or
> some other technique to improve the short and/or long term performance?
> 2) I’ve become interested in Rubidium Disciplined Oscillators recently
> was now thinking of purchasing one of the PRS-10 that I see on Ebay. If I
> did that and replaced one of the DOCXOs from one of the Lucent boxes,
> impact would this have on the overall performance both with and without
> (when in hold-over)? Basically, is it worth the money to upgrade one of
> the boxes to a Rubidium disciplined oscillator assuming the GPS signal is
> rarely lost?
> 3) Figuring the PRS-10 will cost around $250 when all is said and done,
> there a better option to improve my GPSDO system?
> I basically use the GPSDO as a reference for any equipment that takes an
> input. I have no monetary need for a reference, just an interest.
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