Hello Group,
I have read the messages and heard the debates about using LMR-400 or
99/13 type cables with aluminum foil mixed with tinned copper braid,
and the duplex noise it presents when used on the output of the
duplexer to the antenna. I have tried to stay away from this since I
got serious about higher powered ( > 110 watt) transmitters used for
duplex service.
I recently ran across a pile of LMR-400 "DB" I believe it's called,
it has a sticky substance throughout and is said to be water tight.
I used a 90 foot piece of this cable on a VHF repeater running ~ 80
watts out of the duplexer and feeding a very reliable, "duplex noise
free" antenna on the tower.
I couldn't believe the duplex noise I get from somewhere, and I am
thinking it's the cable itself. When injecting a signal through a
directional coupler, I am receiving ~ 0.25 uV for 20 dB SINAD while
running full power. But each time I even think about touching the
feedline, a ton of noise occurs (better than 30 dB of duplex noise).
I have tried both crimp on and compression N-type connectors but no
difference.
The duplexer is a new Wacom with 214 interconnect cables.
Can this LMR-400 really be the cause of noise this bad? There are
two pagers (152.480 and 158.700) about 1/2 mile from the site. No
other transmitters besides a few UHF repeaters. Everything at the
site has an isolator on the transmitter output, including my 2M
repeater. Something is arc'ing somewhere. Any suggestions besides
changing the entire feedline to something more reliable, such as 1/2
inch Heliax or hardline without braid?
Thanks, KC4FWC
Derek.
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