John---
Just read today's emails---seems to me that we can make the assumption that
your repeater system did at one time work to everybody's satisfaction and then
went bad with a desense problem. If this is the case. we are looking for
something that has degraded from being acceptable------its probably not the
time to start redesigning and replacing the system from one end to the
other--but to fix the problem -----especially as you are under pressure to
perform a quick fix.
Now, you mention that your system includes a G7-144 (Hustler) antenna and I
read in your responses, several comments as to the Hustler antenna not being
very good and in fact being the cause of many problems. This is indeed the case
when corrosion sets in-----The antenna can switch from being a fine performer
to a source of totally disabling desense. I say this from experience with the
antenna---I've been there and VSWR readings remained normal.
My problem was that corrosion between the elements of the G7 antenna resulted
in rectification of the transmit energy and generation of wideband noise around
the transmit frequency with sufficient noise energy at the receive frequency
(which went back down the feedline, through the duplexer and straight into the
receiver) to swamp all but the strongest local users.
How do you determine if this sort of thing is responsible for your trouble?
Replace the antenna with one known to be good or if this can't be easily
done-----do some iso "T" testing. Iso "T" testing can be a bit involved for a
beginner and some auxiliary test gear is required which may not be
available----you can read about this in the RB archives. In your case, a simple
antenna change may be easier----just about any antenna will do from an AX-50
on----just be sure that the antenna you try is in good shape and the repeater
won't care.
If I'm on the right track, ask questions---and yes, the G7 antenna can be
rebuilt to better than new---been there and done that ---and am in fact still
using it now.
Scott, N6NXI
----- Original Message -----
From: W3ML
To: Repeater-Builder@yahoogroups.com
Sent: Sunday, October 04, 2009 10:24 AM
Subject: [Repeater-Builder] Radio for repeater use
Hi All,
I am looking at the changing radios on our repeater because of the problems
we are having.
We are using a GE Mastr II into a 6 can duplexer and up via 1/2 hardline to a
G7-144.
However, we can not raise the power above 10 watts before de-sense sets in.
Also the radio will climb in power level as it gets hot.
I set it at 5 watts out and by the end of a half hour net it is up to 12
watts out.
In my opinion this is not right.
What radio would be good for a 2 meter repeater.
Thanks and 73
John, W3ML
