[time-nuts] GPS Antenna Feed Line Decision

Bill Hawkins bill.iaxs at pobox.com
Sun Sep 3 01:37:55 EDT 2017

My HP conical antennas had N connectors, so I used 50 feet of RG-8.
Z3801 receivers never had a problem.

RG-8 is a sturdy cable, which may be the primary consideration for a 38
foot drop unsupported through the mast.

Don't have any comparison to lighter cable, though.

Bill Hawkins

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Clay
Sent: Saturday, September 02, 2017 1:57 PM
To: Time Nuts
Subject: [time-nuts] GPS Antenna Feed Line Decision

Having decision-making problems for the materials for my GPS main
feedline.  Going to use a TM LMR stock, just can't decide how big to go
with it...

26 dB 5vdc antenna on top of a 38 foot mast.  Feed will come down the
inside/center of mast and exit near the bottom, thence routed through a
window and to the GPS distro amp. Antenna will feed GPSDO, NTP Server,
Blitzortung System Blue station, and one other device TBD.

Just cannot decide how big to go with the antenna to distro amp feed...
Assuming 50 feet total (38' mast + 12 feet to amp in shack) @ 1800 MHz
(closest to 1725 MHz), here are the losses from just this piece
(ignoring the amp to device jumpers):

-240 = 5.45 dB XXX - too much loss?
-400 = 2.85 dB
-500 = 2.30 dB  XXX - too hard to find
-600 = 1.85 dB
-900 = 1.25 dB

Money not necessarily a consideration as this is a short run for a
permanent installation.  Don't anticipate ever moving the GPS antenna to
the tower.
For 900 and likely 600, likely would not be able to do it in one piece
as routing it out of the mast and into the shack would get complicated.
Would likely bring it out of the mast at the bottom with a right angle
connector, and then use a smaller diameter jumper for the last 12 feet.
500 is pretty uncommon stock wise and it and connectors are harder to

I already have the tooling for both 240 and 400... but I definitely
don't want to challenge ANY of the devices for signal gain.

So it mostly boils down to easy vs. more effort ($$ aside)....  Is it
worth the additional trouble to move from -400 to -600 or -900?  To NOT
lose the 1-1.6 dB additional?

I'd appreciate your recommendation and reasoning. Thanks in advance!


Clay Autery, KY5G
MONTAC Enterprises
(318) 518-1389

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