I've got a Comet diplexer that has been combining a 2 meter repeater & a UHF
repeater for about 3 years. The antenna was a Comet GP-15 (2m/6m/440) fed
with about 70 feet of 7/8 inch heliax.
While antenna sharing & using a Comet for the repeater antenna was certainly
not my preference, my UHF repeater showed very little if any difference from
the former 8 bay open dipole it had been using in the exact same spot. My
coverage & hearing weak signals seemed to stay about the same. The UHF
duplexer is a Phelps-Dodge 6 cavity pass/reject going in to a Micor receiver
with an ARR pre-amp and an extra Motorola pass cavity. The transmitter is 30
watts.
I can't answer for any changes on the 2 meter side as it is not my repeater &
was a new addition to the location. (a LOOOONG complicated story in ham radio
politics brought me to the situation of sharing my location) The 2 meter
duplexer is a Tx-Rx 4 cavity reject only. The transmitter is 30 watts.
The changes I did make:
On the Comet diplexer, I removed the UHF connectors & replaced them with N
connectors. I re-inforced the connections to the center pins & made sure the
grounds of the connectors were very well grounded to the shell of the
diplexer. I also insisted that the other repeater use Rg-214 for their
jumpers & I gave them about a 20 foot piece to make their jumpers with.
Our repeaters are about 10 feet apart from each other.
My system already used Rg-214 for all jumpers except for one very short Rg-223
jumper in a tight spot.
The only troubles I did have was audio from the 10 watt college FM radio
station coming in on audio input for my internet connection to the repeater.
A few ferrite beads immediately stopped it. (their antenna is about 20 feet
above mine)
------ Original Message ------
Received: Wed, 02 Feb 2005 07:36:41 AM CST
From: "derek_mcintyre" <[EMAIL PROTECTED]>
Subject: [Repeater-Builder] Re: Homebrew a 2M/440 crossband coupler?
> Thanks for all replies. I have several of the Comet diplexers with
> PL-259's, one "Pro-Am" model, one Larsen, and one made by Daiwa. One
> person commented on the duplex noise and I tend to get alot of this
> from all of these except the Larsen, which burnt up several years
> back with 60 watts of UHF running through it. A 3.3 pico capacitor
> smoked, and I replaced it with two 5.6's in series and all worked OK,
> but I had to run the power down a little in order to keep things from
> smoking again. If you look closely the paperwork on the comets and
> diamonds say "200 watts" but in the fine print, it says 200 watts SSB.
>
> I am planning to run one line of 7/8 up a 350 foot tower, but want 2M
> and 440 repeaters, with two separate antennas. I don't want to use a
> dual band antenna because the fiberglass comet and diamonds seem to
> disappear when hit by lightning.. I'd rather use 2 separate antennas
> and one feedline, and split it once up top and once on bottom. I
> plan to put the diplexer in a box atop the tower.
>
> One person mentioned replacing the pigtails on the unit to make the
> duplex noise disappear. I replaced the ones on my Daiwa unit with
> some small hardline used on microwave equipment that is RG-58 sized.
> The duplex noise went away. Thanks for the suggestions.
>
> 73, KC4FWC
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