Rick;
I think you need to isolate whether it is tx through the
duplexer or something else bothering the rx and or squelch. It sounds
like the tx signal fundamentally is clean from your analysis so far..
in order to isolate through the duplexer, connect the tx directly to
a dummy load instead of it's side of the duplexer while injecting rx
into the duplexer. if it does not cycle, the tx is sending something
through the duplexer to the rx....if it does cycle.. it is an
internal issue as you suspect.. I would use the tx to duplexer cable
in the dummy load path as you want to see if some radiation from it
is part of the equation.
I lean more to spurious on initial keyup... causing a noise burst
maybe due to exciter tuning... but this test should tell you if it is
conducted internally or passed through the duplexer.
Doug
KD8B
At 05:04 PM 12/17/2008, you wrote:
>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
>
>
