As the others already said, you MUST have very well shielded jumpers. RG-214
will do if you have some, otherwise go with super-flex hard line. Both are
often available on eBay. Try to stay away from the LMR coax, as it consists
of a braid and foil shield which expand at different rates and cause all
sorts of noise problems. Great as far as shielding goes, however. Super-flex
cable is corrugated and has just a copper outer conductor so no metal
expansion to worry about, but it can't be bent too many times. Excellent for
use in and around repeaters and will work well outside if you tie it down
properly. You may want something larger than 1/2 inch depending on the loss
your system can tolerate.

Depending on your Tx/Rx spacing, you could get away with less than 95 dB of
isolation in the duplexer, but a 4-cavity unit will give you about 80 dB at
best, so you really want a 6-cavity unit. Alternatively, a very tight
receiver might help you, such as a Motorola Micor or MSF5000.

The antenna could also be a source of desense. There aren't many ways to
prove where the desense is coming from, but a good spectrum analyzer on the
receiver's antenna input might tell you if you're getting signal directly
from the transmitter, through the duplexer, or back from the antenna.

Connect a dummy load to the output of the duplexer and use a signal
generator to key the repeater. Check if you still have desense that way. If
so, the problem is in your cables and/or duplexer and/or repeater. If not,
it's a function of the antenna and feed line.

A friend of mine is having a similar problem and he has gone through all the
appropriate steps. His desense appears to be coming down from the antenna,
and in his case it takes an additional 15-20 dB of signal (using a signal
generator) to keep the repeater open once the transmitter comes on. I can't
tell you how many S-units that is, but it's still a lot of signal, and he
has a 4-cavity duplexer and is running a 1 MHz split. Operation with a dummy
load is 100% perfect, so his problem is external to the equipment.

Unfortunately, if the signal is coming down from the antenna, then you could
have a 60-cavity duplexer and it wouldn't eliminate the desense.

Bob M.
======
"Robert Kubichek" wrote in message
...


1st Use superflex 1/4 - 3/8 hardline jumpers between duplexer and
repeater....
2nd Make sure that if the duplexers are in the same cabinet as
repeater,put some sort of shield between the two...
3rd Use at least 1/2 inch, preferrably 7/8 hardline from cans to
antenna, as even the LMR coax is still more lossy at 2M...
4th Make sure all connecters cables are solidly connected.
5th Use a poly phaser lightning arrester as it will ground cable,
and make sure cabinet(s) are/is grounded, with a good earth ground.


Get rid of the RG8 superfoam and go with hardline!!!!!!
That's causing a lot of your problem..... too much loss of signal.

I used to run a 2M repeater, and I found that the above are a must for
good reception.. Also Hamtronics is correct, you should have a better
set of duplexers, my old set was around 105db isolation( 6 can set about
30" tall) and I put them in thier own metal cabinet.

Good luck

Bob N9LVU


Hi guys. Thanks in advance for any help. Please post
responses in NG as my email 'reply' address is fake
since some don't know how to mind their manners.
I recently put back into service a Hamtronics REP100
two meter repeater with a new Telewave Duplexer and
the antenna is a Ringo Ranger II with radials. Coax to
the antenna is RG8 superfoam and jumpers between
repeater and duplexer are RG8 superfoam.
Here is the problem. I am experiencing 'desense' on
the repeater to the point where it takes a signal of S5
or better to get in. A lesser signal just makes the
repeater "chop" (continually opens and closes the
transmit side. The Duplexer was factory tuned
(for what it was worth) and I did 'tweak' it and got a
much noticible improvement. Before tweaking, it took
an S9 or better to get in. I realize I should be running
(supposedly) double shielded jumpers from repeater to
the Duplexer, but I can't imagine they are going to make
that much difference. I am also told to mount the duplexer
in it's own enclosure (it's rack mount so that would be cute)
to keep it away from the repeater.
The Hamtronics manual says you HAVE to use a
duplexer with at least 95 db of isolation (try to find one)
and mine is 77db. I really can't imagine there is not
enough isolation, because I know where there are other
machines running with old duplexers with much less
than 77db of isolation. Just to add to the mix, I sent
the repeater up to Hamtronics and had it tuned and
checked out and it is 100 percent, so I *suspect* it
is not a repeater problem. (Someone suggested to
try killing some of the sensitivity of the reciever).
So....looking for ideas and suggestions on what to try
next (other than double shielded jumpers to the duplexer).
Thanks for any help or ideas...
73's Rick