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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