[time-nuts] GPS antenna installation problem

Jim Palfreyman jim77742 at gmail.com
Sun Mar 1 18:06:38 EST 2009


All those lengths and temperatures in some weird old fashioned measuring
system make my head spin.

2009/3/2 Bill Hawkins <bill at iaxs.net>

> 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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