I don't know what type of service monitor you are using, but I tend to use an
iso-tee to measure desense with the duplexer hooked to a dummy load through the
iso-tee. It might be possible for the service monitor to contribute to some
signal reflection if it is used as the power termination.
Make sure the cables to the duplexer are double shielded, like RG-214, and
inspect the connectors to make sure all the grounds are in good shape. Check
the internal cables in the VXR-7000 for the same potential problems.
I may be preaching to the choir and if so I apologize.
73 - Jim W5ZIT
--- On Wed, 12/17/08, pontotochs <pontoto...@bellsouth.net> wrote:
From: pontotochs <pontoto...@bellsouth.net>
Subject: [Repeater-Builder] VXR 7000 with desense
To: Repeater-Builder@yahoogroups.com
Date: Wednesday, December 17, 2008, 4:04 PM
Hi,
I've checked the previous posts on this issue, but I am hoping that
there is more light to be shed.
We have a VXR 7000 that has had issues for a while as a two meter
repeater.
In the shop we set it up with its DB 4026 duplexer and 50 ohm dummy
load and monitored the output power with a Bird thru line watt meter.
We used a service monitor to inject the RX signal to get 10 dB
quieting (approx 0.2 micro volt). Put the unit into repeat mode and
the repeater will cycle (go in and out of transmit) until the RX
signal is increased about 20 to 25 dB (approx 3.6 micro volt).
Looking at what is coming in the receive port with the transmitter
is keyed is about -75 dBw (50 watt out with about 95 dB of isolation)
at the TX frequency, and there is little to no hash at the RX
frequency - seeing the noise floor of the spectrum analyzer (-120 dB).
Put the 7000 into base station mode, hooked up second signal source,
set first signal source to give 10 dB quieting at the RX frequency
(0.2 uV), set the second signal source to emulate what we saw from the
duplexer (79 mV at TX frequency) and there was no desense. Increased
the simulated TX voltage to better than 1 volt and still no desense.
My thought is that something has gone bad internally within the
7000. Is there something else I need to try?
Thanks in advance for your help.
Regards,
Rick, N5RB
