[time-nuts] Re: Stability question

[va2hdd at ebox.net]

Hi Jack.

At work I had to bring GPS signal to one of our labs, which is in the 
middle of a building with no rooftop access or nearby window. The only I 
was able to do it was to bring a long run of LMR400 cable from my 
rooftop antenna on top of the building which connects to a GNSS splitter 
amplifier in the middle of the path; and then another long LMR400 cable 
connected to a second splitter and from that second splitter I 
distribute the GPS signal to the clocks that sync our lab equipment. The 
total cable run from the antenna to the first splitter is 60 meters (196 
feet). The cable from that first splitter to the second splitter is 70 
meters (229 feet), and at the output of the second splitter I have 
cables from 5 meters to 25 meters to bring the signal to each clock. 
Even with this far from optimal setup I have not experienced 
insufficient signal level or signal loss problem.

That being said, I had problems with two older Datum ExacTime 6000 and 
6010 clocks that would take forever to lock or receive only 2 or 3 
satellites. They also were affected by a GPS epoch problem.  So I 
attempted to cure their problems with a GPS receiver upgrade made by a 
French company called HEOL designs : https://www.heoldesign.com/, the 
exact product is : 
https://www.heoldesign.com/N024-GPS-receiver-board-for-Tymserve-2100?lang=en 
. With the receiver upgrade the long lock delay and intermittent signal 
loss problems disappeared, and the epoch rollover bug was cured, BUT 
although the clocked was locked and correcting the "LOCK" LED was never 
on. It seems that the upgrade board is fully compatible with the 
TimeServe 2100 but only partially compatible with the ET6000.

So I junked the two ET6000 and replaced them with more recent vintage 
clocks and all is OK since I installed the replacement clocks.  For some 
strange reason clocks of similar vintage as the ET6000 always synced OK 
and they still sync perfectly, like an ancient TrueTime NTS-100i.

Of course this is my experience and things might be different for you.


Claude

Le 02/03/2022 18:49, Jack Davis a écrit :
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> 
> I have a Datum Exactime ET-6000TCXO that I use to lock all my test
> equipment to 10 MHz.  My GPS antenna is approximately 200 feet from
> the receiver and I have intermittent GPS signal levels and associated
> unlocking of my ET-6000TCXO.  I have tried using bigger less loss coax
> cable but its just not enough to make it reliable.
> 
> 
> 
> I see there is a Symmetricom Kit 142.6150 consisting of a model
> 140-615 GPS antenna / downconverter and a model 150-615 upconverter
> available to allow longer runs of coax cable.  From what I can tell
> there is a local oscillator in the antenna that down converts the
> 1,575.42 MHz GPS signal to 4.092 MHz for lower cable loss.  The up
> converter on the receiver side apparently another local oscillator
> that up converts the 4.092 MHz IF to 1,575.42 MHz.
> 
> 
> 
> My question is: will the two local oscillators and the up and down
> conversion cause phase noise or frequency instability of the GPS
> signals into my ET-6000TCXO?  It does have some sort of flywheel
> correction internally but is it enough to keep the 10 MHz timebase
> stable?
> 
> 
> 
> Thanks,
> 
> Jack  K6YC
> 
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