[time-nuts] Re: Symmetricom/Datum FTS-1050A Disciplined Frequency Standard

[Michael Garvey]

>>It was model FTS-1050A Disciplined Frequency Standard.
The FTS-1050A was the second product of Frequency and Time Systems Inc
(FTS) and appeared in the market around 1980.  The instrument architecture
was the product of Martin Levine (of Levine and Vessot Gravity Probe A) as
implemented by Jerry Welch.  The 1050A employs an analog PLL.  The heart of
the 1050A instrument was a 1000A quartz oscillator designed by Donald
Emmons.
Most of the FTS, Datum, Symmetricom products relied upon trade secrets for
protection of intellectual property which is why you'll find few patents or
detailed technical manuals.
The Datum 2110B, developed first at Austron (Austin, TX) was a similar (to
the 1050A) instrument which used a digital FLL.  The 2110C (based upon the
2110B and developed in Beverly, MA), was a more sophisticated (though not as
low noise) version with a dual input FLL that would discipline to the
average of two reference inputs and, upon loss or severe degradation of one
input, would switch to the use of a single reference input. The primary
application was for robust, redundantly referenced timing sources for
telecom Central Office instruments.  The design was by Peter Vlitas.
I was a scientist at FTS then CTO, retiring in 2011.
Mike Garvey

-----Original Message-----
From: Joseph Gwinn <joegwinn at comcast.net> 
Sent: Monday, April 18, 2022 6:18 PM
To: time-nuts at lists.febo.com
Subject: [time-nuts] Symmetricom/Datum FTS-1050A Disciplined Frequency
Standard

On Wed, 06 Apr 2022 03:30:35 -0400, time-nuts-request at lists.febo.com
wrote:
time-nuts Digest, Vol 216, Issue 10

>>> 
>>> Message: 4
>>> Date: Sun, 3 Apr 2022 09:53:18 -0400
>>> From: Bob kb8tq <kb8tq at n1k.org>
>>> Subject: [time-nuts] Re: Low Phase Noise 10 MHz bench signal source
>>> 	sought
>>> To: ew <ewkehren at aol.com>, Discussion of precise time and frequency
>>> 	measurement <time-nuts at lists.febo.com>
>>> Message-ID: <11376923-062A-4011-A6D4-1D9CE3361466 at n1k.org>
>>> Content-Type: text/plain;       charset=utf-8
>>> 
>>> Hi
>>> 
>>> These days a PLL is going to either be analog or digital. If it’s 
>>> analog, you get into size constraints related to capacitors as you 
>>> go to lower crossover frequencies. With digital, you get into all of 
>>> the noise issues that any digital circuit will have.
>>> (Yes, they can be addressed but it’s not easy at very low offset 
>>> frequencies).
>> 
>> All of the loop filters I've seen recently had nominal bandwidths in 
>> the Hertz to tens of Hertz, usually implemented in some kind of 
>> digital signal processor.
> 
> 10 Hz or higher is certainly do-able with analog loop components. 
> There are a lot of products out there that work that way.
> 
>> 
>> About 30 years ago, there was a legacy 5 MHz disciplined oscillator 
>> that could be set to a 100-second response time.  I never did find 
>> any real technical data or patents on it.  I don't recall its name, 
>> but it may come back to me.  I think it was made by Symmetricom.

I finally recalled the details, after all these years.  It was from
Symmetricom, they having acquired Datum in 2002.  It was model FTS-1050A
Disciplined Frequency Standard.  Despite the implication of the product
name, it does appear to be a phase-lock loop design at heart, from the users
manual (my copy being dated 1999).  This is the one that I suspect was in
fact a 3rd-order PLL design, because it would become unstable if the the
incoming reference were too faint, being far more fussy than your usual PLL,
which would happily lock onto a pretty faint and ratty reference signal.

It has two switch-selectable integration periods, one second and one
hundred seconds.  I assume that the integration is digital, but in hardware
versus a computer.

I can provide the documentation, if anybody wants a copy.  Apparently a
number of folk were looking here, over the years.  Maybe something to add to
Febo.com.

I wonder who the designers were.  Hmm.  I bet that Robert Lutwak, William
Riley, and Kenneth Lyon were involved, as these folk are the inventors of
patents assigned to DATUM TIMING TEST AND MEASUREMENT Inc and Datum Inc in
the day.  I worked with Ken Lyon some time ago, if I have the right Ken
Lyon.


Joe Gwinn
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