I'd be willing to bet your noise problem is site related and has nothing to do
with the feedline. Rusty wires and rusty metal can cause micro-arcing just like
the shield/braid problem in the LMR400 cable, especially in windy conditions.
The problem is your options are limited in trying to find and fix these noise
sources.
With the system being noisy and you physical present at the site, cap off the
feed line at the antenna with a dummy load
and check for noise. If there's still noise, It could be the feedline, duplexer
or a repeater TX problem.
If the dummy load trick eliminates the noise, Try using a separate antenna for
RX and TX, and run them into the cans without the "T" connector. If you can get
some decent vertical separation > (40ft.) , this might be worth a try. This
will provide more isolation from locally generated noise.
Steve
WA6ZFT
>
> From: "derek_mcintyre" <[EMAIL PROTECTED]>
> Date: 2005/01/17 Mon PM 12:40:14 EST
> To: Repeater-Builder@yahoogroups.com
> Subject: [Repeater-Builder] Duplex noise/LMR-400 w/sticky stuff?
>
>
>
> 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.
>
>
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>
>
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