[time-nuts] GPS antenna installation problem

Bill Hawkins bill at iaxs.net
Sun Mar 1 15:05:00 EST 2009


Group,

My GPS time system consists of two Z3801A receivers with two HP cone
antennas.
I built a mast from plastic pipe (6" base to 2" arms) that is about 16
feet tall.
The antennas are 4 feet apart, each 2' from the center of the mast. The
mast
rises from a deck and is fastened 8' up at the roof line. The mast sits
on a
3/4" sheet of high density marine plastic fastened to the deck with
stainless
hinges so that the antenna can be folded away from the house and brought
to the
deck railing. The mast was put up in 2003.

The antenna cables are each half of a 100' coil of RG-8U. Each cable is
about
half in the house and half outdoors. N connectors are soldered to both
ends, so
no adapters are used. The cables leave the house through a waterproof
boat deck
fitting and travel about 5' under the deck to the mast. There's a
service loop
to allow the mast to be lowered, then the cables rise unsupported
through the
mast pipe and branch out to the antennas, which support the weight of
the cables.

Oh, and the location is Minneapolis, MN, USA.

The problem is loss of signal during cold weather. Last winter (07-08) I
lost
the signal from one antenna during a cold snap, but it came back a week
or so
later when it warmed up outside. This winter, I lost The North antenna
on Nov
22 when the low was 15, and it didn't come back. Then the South antenna
went
away on Dec 24 with a -17 low and didn't come back. I'm still running on
holdover.

I suspect that it's not a good idea to hang 20 feet of RG-8 from an N
connector
without some kind of strain relief, but I don't know why that would be a
cold
weather effect. Perhaps the center conductor shrinks more than cable and
its
braid, and pulls the center pin out. There's definitely an open circuit,
looking
at the receiver end of the cable. There's no alarm from the Z3801.

Any thoughts, comments or ideas?

Bill Hawkins





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