Dave, just out of curiosity, can you remove the can, say run only four of them,
and get all to work ok on the system. Also, what would happen if you changed
the placement of the can, say if this is in your tx side, move it to the rx
side, could be a bad spot in the cap, but may be good in another spot. Just
some thoughts. If this is the first can in the series, from the antenna port,
what does the connector look like, ie burns, color, etc....
Mathew
ve7ltd <[EMAIL PROTECTED]> wrote:
I was helping a local group tune a 6 cavity Sinclair Q2330 VHF
duplexer. With a spectrum analyzer, I was able to get the pass/notch
looking really good into a dummy load.
I did notice that one of the capacitors did not tune linearly. All
of the other caps would tune the notch smoothly as it approached the
correct notch frequency. This one cap would tune weird. As you
rotated it on one direction, it would tune the notch closer, then
farther, then closer, then father. All the other caps would only
move linearly in one direction when rotated.
When hooked up at the site, there is not a lot of loss either on the
RX or the TX. But as soon as the transmitter comes on, no matter
what the power output, there is a huge amount of RX noise generated,
whether terminated with a load or the antenna. The noise is also
intermittent - It comes and goes. If that suspect cap is turned
under any transmit load, it crackles loudly. None of the other caps
exhibit this behaviour. The noise desenses the receiver badly.
I have not scoped the transmitter yet, but it was working fine when
removed from service (GE MASTR II 40 W station). I also have used
and tuned many of these in the past, and they all have worked fine.
There was signs of lightning damage on an old antenna they removed
from the site a few years ago (the cable harness in a Sinclair 210C-
4 was burned in one dipole. I am unsure if they replaced the
feedline. There is no reflected power.
The duplexer also was originally tuned in the low 160's and I am
aware that the harness may need to be changed.
Here are my questions:
1) Besides the weird behaviour, is there any way to test if the cap
is bad?
2) If there is lightning damage, where/how may it be visible? Is it
repairable? Where would I find a replacement cap?
3) Does the fact that the system works fine with a signal generator
and sprectrum analyzer suggest that the problem is in the duplexer?
I have set up many repeater systems, and never had a problem like
this before. Any ideas?
Thanks all. This group is a great resource for people like me that
want to get into repeater building. I would not be able to be where
I am without the help you all provide.
Dave Cameron
VE7LTD
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