Rick
That pretty much sounds like a inadequate duplexer or a
dirty transmitter making noise.. You might check hamonics as they may
sneak through the duplexer with enough power to desense the rx...
initially it sounds like the tx is pretty clean but something is
getting through to the rx....
I would connect the spec an to the rx port of the duplexer and watch
to see what jumps with ptt pushes... look at harmonics and open the
window... any jump at the noise floor would be suspect...
Doug
At 04:56 PM 12/18/2008, you wrote:
>Thanks to all who have responded. A quick up date.
>
>Putting the dummy load on the TX port of the repeater (replace the
>duplexer with a dummy load) has shown that the repeater works without
>cycling - so my initial thought of something going on inside the
>repeater is out the window... (Thanks Doug)
>
>If is was spurious TX trash while the transmitter was coming up, then
>after we overcame the desense with the service monitor and the TX
>stabilized, then when we turned the service monitor back down, the TX
>should have stayed on, but it didn't and started to cycle again
>
>Still racking the grey cells,
>Rick, N5RB
>
>--- In
><mailto:Repeater-Builder%40yahoogroups.com>[email protected],
>"pontotochs" <pontoto...@...>
>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
> >
>
>
