[time-nuts] GPS discipline oscillator vs phase lock

Brent brent.evers at gmail.com
Wed Jun 21 11:54:36 EDT 2017

Jim -

Your first thread in this post was fascinating to me - stuff I'd never been
exposed to.  It seems like the 'tricks of the trade' for so much of how
things actually get done are so often only accessible to those who work
closely with them.  I was about to shoot you an email to ask if there was
any reference (other than piles of journal articles) that cover some of
these topics, when I scrolled down and found this post with the Descanso
links and references.  What a trove!  There's more info in the links on
that page than I could ever hope to comprehend.

Many thanks for this post.  It will remain marked and in the back of my
brain as "stuff that you should learn".  If we only ever had enough time.
Why didn't anyone ever expose me to this stuff when I was young and just
starting in RF?


On Sun, Jun 18, 2017 at 1:36 PM, jimlux <jimlux at earthlink.net> wrote:

> On 6/18/17 7:10 AM, Attila Kinali wrote:
>> On Sat, 17 Jun 2017 06:29:02 -0700
>> jimlux <jimlux at earthlink.net> wrote:
>> Well, at JPL we regularly lock two crystal oscillators together that are
>>> over a billion km apart with added Allan deviation of less than 1E-15 at
>>> 1000 seconds with a radio link at 7.15 GHz.  It's how we measure the
>>> distance and velocity to spacecraft (a few cm in range and mm/s in
>>> velocity) and from that figure out the gravitational fields (among other
>>> things)
>> This sounds interesing. What do I have to google for to learn more?
> It's just how we do radio science/ranging - you transmit a spectrally pure
> signal from earth (typically oscillator locked to a maser), at the
> spacecraft you have a very narrow band PLL (traditionally a VCXO) that
> locks to the received signal, and you generate the downlink signal from
> that same oscillator, transmit it back to earth, and compare.
> The transmitted signal is precisely in a specified ratio with the received
> signal (880/749 for X-band 7.15 GHz from earth, 8.4 GHz coming back). For
> Ka-band, the earth signal goes up at 34 GHz, and comes back at 32 GHz
> A typical spec is that the transponder introduce no more than 4E-16 ADEV
> at 1000 sec.
> https://descanso.jpl.nasa.gov/ has links to a whole bunch of useful
> references
> https://descanso.jpl.nasa.gov/monograph/mono.html
> specifically volume 1 by Thornton and Border talks all about radiometric
> ranging.
> The various design and performance series describe the specific
> implementations.
> Joe Yuen's "Deep Space Telecommunications Engineering"
> https://descanso.jpl.nasa.gov/dstse/DSTSE.pdf
> Chapter 3 covers receiver design
> Chapter 4 covers radio tracking
> --
> Then you can look for papers on "deep space transponder"  The classic
> design papers are in the 90s.   IEEE MTT, and the JPL IPN progress reports.
> The Cassini Deep Space Transponder is sort of a progenitor of them - then
> there's the Small Deep Space Transponder (SDST) designed in the 90s, flying
> 2000 through now.
> Somewhere around 2000, the design started moving away from trying to lock
> the oscillator to doing the phase lock and phase/frequency turnaround in a
> digital loop, with a fixed oscillator driving DDS or NCO.  At JPL, this
> would be the "Advanced Deep Space Transponder", but Thales Alenia Space
> Italia (TASI) uses a similar approach for their deep space transponders
> (look for Juno and BepiColombo)
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