Hi

The first gotcah is that the distinction is not very clear. A TBolt varies the frequency of
the OCXO in the GPSDO. GPSDO’s that use Rb’s can and often do vary the frequency.

Indeed some devices use a DDS to generate an output rather than varying something else.
I suspect that is what you are bumping into. In some cases a DDS feeds a cleanup loop or filter
that restricts the output range.

If you are after low noise at 10 GHz, the multiplier chain needs to be carefully designed. There
is a lot more to it than you might think. The first and most basic question would be “is it a fixed
frequency output or tuned?”. From there you can head off in a number of directions.

If you need to be able to change frequency from 1 MHz to 10 GHz in a few nanoseconds, then
there is no alternative to using a DDS. If hat is part of the requirement then you go from there. If
you want only 10 GHz +/- 0.001Hz then there are other, more quiet / lower spur ways to do the job.

Indeed it goes on and on …..

Bob

I also see terms like GPS tamed or PLL-GPS. 
https://www.ebay.com/itm/1pcs-PLL-GPSDO-10M-GPS-tamed-clocks/263392170249?hash=item3d53659109:g:1p0AAOSwH3haNo7c
https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313.TR12.TRC2.A0.H0.Xgps-pll.TRS0&_nkw=gps-pll&_sacat=0
It is not at all clear which one is what type and how it is designed. 

Even in main well known brands, I understand PRS10 and sa.22C and fe5650 are fundamentally different.
I guess they are all "GPS disciplined" in some way but for a newbie, telling one apart from the other and picking a suitable architecture for the purpose is very difficult.

(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG

On Wednesday, September 25, 2019, 9:28:29 PM EDT, Bob kb8tq <kb8tq@n1k.org> wrote:  

Hi

The first gotcah is that the distinction is not very clear. A TBolt varies the frequency of
the OCXO in the GPSDO. GPSDO’s that use Rb’s can and often do vary the frequency.

Indeed some devices use a DDS to generate an output rather than varying something else.
I suspect that is what you are bumping into. In some cases a DDS feeds a cleanup loop or filter
that restricts the output range.

If you are after low noise at 10 GHz, the multiplier chain needs to be carefully designed. There
is a lot more to it than you might think. The first and most basic question would be “is it a fixed
frequency output or tuned?”. From there you can head off in a number of directions.

If you need to be able to change frequency from 1 MHz to 10 GHz in a few nanoseconds, then
there is no alternative to using a DDS. If hat is part of the requirement then you go from there. If
you want only 10 GHz +/- 0.001Hz then there are other, more quiet / lower spur ways to do the job.

Indeed it goes on and on …..

Bob

It might be a bit of an over-simplification to split oscillators in
those two camps, "fixed" and "agile". There are often many trade-offs in
performance that you have to deal with. Moreover if you are getting your
oscillators from eBay, or especially parts from China, you may also have
to assume that original factory specs are no longer valid.

This is one reason why the time nuts list is so preoccupied with making
accurate measurements of frequency standards. You only know what you
have if 1) you buy it new from a reputable company, or 2) when you buy
it cheap and measure it yourself with reputable test equipment, or 3)
you get it from a friend who has measured it for you.

If you're asking specifically about Rb, I think the data shows that hp
5065A has best performance, followed by PRS10, followed by all the cheap
telecom Rb. Sorry, I don't have plots or URL's handy at the moment to
support this with real data. My main take-away is to start with your
requirements, see which products / specs meet that, and if you're buying
dirt cheap surplus, make your own measurements to validate your
requirements.

/tvb

On 9/25/2019 3:45 PM, Taka Kamiya via time-nuts wrote:

Maybe that "GPS tamed" is literally translated from chinese for "GPS
disciplined". It is indeed the disciplining that gives personality to
the GPSDO. You can PLLize the OCXO's 10MHz or the PPS derived from the
OCXO's 10MHz and see different results on the 10MHz's stability and
accuracy. It seems that Chinese built GPSDOs are derived from the
BG7TBL's design, you can find performance data here:
http://www.ke5fx.com/gpscomp.htm

On Thu, Sep 26, 2019 at 8:00 AM Taka Kamiya via time-nuts
time-nuts@lists.febo.com wrote:

Tom,
I know you are absolutely right.  When I buy from eBay, I have no idea where they came from.  Reject pile, junk yard, or pristine clean room.  Unfortunately, I can afford up to certain amount.  I have lots of PRS10 but their origin is unknown.  Even if I buy 5065A, origin will be unknown and so as condition.  Recently, I called around local cal-lab to see who can help me validate these devices.  No one could.  I'm very tempted to buy T-bolt or PRS10 new but at $1500, it's quite hefty.  I may just have to.
I'm at learn as much as I can stage.  I have a Cesium but it's old.  4040/A  I have no idea how it was used or stored.  It would be nice to have one known good standard.  The best I can do for now is my array of GPSDOs.  (from unknown sources)

(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG

On Thursday, September 26, 2019, 3:05:19 AM EDT, Tom Van Baak <tvb@LeapSecond.com> wrote:  

It might be a bit of an over-simplification to split oscillators in
those two camps, "fixed" and "agile". There are often many trade-offs in
performance that you have to deal with. Moreover if you are getting your
oscillators from eBay, or especially parts from China, you may also have
to assume that original factory specs are no longer valid.

This is one reason why the time nuts list is so preoccupied with making
accurate measurements of frequency standards. You only know what you
have if 1) you buy it new from a reputable company, or 2) when you buy
it cheap and measure it yourself with reputable test equipment, or 3)
you get it from a friend who has measured it for you.

If you're asking specifically about Rb, I think the data shows that hp
5065A has best performance, followed by PRS10, followed by all the cheap
telecom Rb. Sorry, I don't have plots or URL's handy at the moment to
support this with real data. My main take-away is to start with your
requirements, see which products / specs meet that, and if you're buying
dirt cheap surplus, make your own measurements to validate your
requirements.

/tvb

On 9/25/2019 3:45 PM, Taka Kamiya via time-nuts wrote:

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

On Wed, September 25, 2019 5:45 pm, Taka Kamiya via time-nuts wrote:

That is a bit oversimplified.  GPSDO is "GPS disciplined oscillator,"
meaning that the output frequency of the oscillator is forced to follow
the inverse of the time measurements derived from the Global Positioning
System.
Obviously if the oscillator has to follow another reference it cannot
truly be fixed frequency on the output, but there are various different
ways that the frequency can be varied.  Depending on the important
parameters for your needs the differences in mechanism may or may not be
important.

You are mixing different types of equipment together, so it is a little
difficult to know what you are asking.
FE5650, PRS10 and SA.22C are rubidium frequency standards.  A rubidium
frequency standard is fundamentally an OCXO which is slaved in a frequency
lock loop to a way to measure atomic transitions in rubidium vapor.  There
are various systematic errors which pull the frequency of that atomic
transition measurement, so a rubidium standard will commonly have an
adjustment mechanism that can adjust the output frequency far enough to
compensate for those systematic errors, but you need a more accurate
device for comparison for that adjustment to be worthwhile.

A Thunderbolt is a complete GPS disciplined oscillator system which
accepts GPS signals from an antenna, and outputs 10MHz which is slaved so
that on average there are always 10 million output transitions per
GPS-derived second estimation, and outputs a pulse once per second which
occurs on  the transition of the GPS-derived second estimation.

When the GPS signal is not available for some reason (antenna failure, GPS
system problems, etc.) the GPS disciplined oscillator has to run in
undisciplined mode.  Over that time the corrections to the oscillator
frequency are not available, so only the intrinsic stability of the
oscillator used sets the long term stability of the output frequency.  In
that particular case (no GPS available) a GPSDO using a rubidium
controlled oscillator as part of the design will have more  stable long
term frequency than an oven quartz oscillator.
While GPS signal is available to measure and control the output frequency
there is little difference between an ovenized quartz and a rubidium
controlled (which recall also has an ovenized quartz oscillator driving
the output, but has a control loop using rubidium vapor transitions to
correct any frequency drift of the quartz oscillator).

A very good place to start is searching for John Vig oscillator tutorial.
John Vig has a lengthy presentation about all things relating to
oscillators, if you can find the version which includes the notes along
with the presentation slides you can spend a couple of days studying that

Mixing different types of things into a single question again.
The term PLL is phase locked loop, it is a particular type of control loop
design which measures the edge transitions of a reference frequency input,
the edge transitions of an output signal, and controls the output so that
the edges match the reference.
You can phase lock quartz, rubidium, pendulum.  Maybe an hour glass, but
the only transition I can think of is when you turn the hour glass over,
so that  would be an impractical PLL.

No, SA.22C and FE5650 have no connection to GPS,  they are not GPS
disciplined in any way as stand alone devices, but can be used as part of
a full GPS disciplined oscillator design. The SA.22C has a
pulse-per-second (PPS) input, so it can be connected to GPS, but that gets
into a lot of secondary questions relating to how that PPS is derived and
whether it helps or hurts overall stability.

--
Chris Caudle

On 9/26/19 6:15 AM, Chris Caudle wrote:

https://tf.nist.gov/sim/2010_Seminar/vig3.ppt

Hi

There are some “simple” answers to this:

1. You can (and many of us do) set up to measure things yourself. For most setups this means
   comparing devices, but indeed Time Nuts seem to have piles and piles of devices. You can do this
   with shiny new gear (possibly for a lot of money), eBay versions of the same stuff (hopefully for
   less money) or with home brew / DIY gear. Phase noise and the various xDEV’s (like ADEV) can
   be measured this way.

2. You do need to figure out what the objective is. If it’s microwaves then the test gear needs to
   run to those frequencies. If it’s just 10 MHz then not so much. If you do indeed anticipate having
   gear at the 1x10^-15 @1 sec level then your setup needs to be a bit fancier than if “only” 1x10^-11
   is what you are after.

3. If this is cost constrained, be realistic about the costs. It is very easy to say “max $100” and then
   start talking about many thousands of dollars of gear. It is also easy to start with a budget and have it
   creep on and on and on. Even projects funded by national governments (with far larger charge cards
   than any of us have) hit limits in terms of costs. It is part of this at any level.

It’s easy to say that you are setting up a full lab. If so, a hydrogen maser (possibly two or three of them)
could be part of the mix. There are Time Nuts who have set up that way, but very few of them. Short
of setting up that way, you will be in a compromise situation. (Indeed even a maser is a bit of a compromise
compared to other more exotic gear). Some degree of focus will be needed. Few of us have a really good
handle on that “focus” thing …..:)

Another wrinkle to this is that there are indeed measurements and terminology that are a bit unique to
the field. Indeed the measurements and gear that were common in the 1950’s have evolved into something
a bit different today. The same is true if you go back into the 1930’s. Different disciplines focus on different
measures, even today. Tying papers, spec sheets, or measurements from one era or discipline to another
can be challenging. There is no one universal single number that measures “best”.

So yes, it’s complicated and it can be confusing. Welcome to why it’s called Time Nuts :)

Bob

I have a number of revisions of the John Vig tutorial in my Manual pages.
The most recent was sent to me directly by John but I am not sure if it has
the notes.
www.ko4bb.com
Go to Manuals and search for Vig

Didier KO4BB

On Thu, Sep 26, 2019 at 7:03 AM Chris Caudle chris@chriscaudle.org wrote: