Hi Skipp,
Thank you very much for your very informative message, and you seem to
be right on. I just went trough it quickly and will reread it again
shortly in order to send you some specific answers. But in the mean
time please allow me to send you a copy of some information about
tests we have performed in the last few hours, as they might be
usefull (I hope) to better understand what is happening with the
system. Please keep in mind this text was sent to a third party so
there might be some references that do not apply to you directly.
Thanks again for your help and time, as it is very much apreciated.
Bellow please find the copy of said message.
Alex
=======MESSAGE COPY================
Well today is radical testing day. Last night we disconnected all the
Fylde equipment from the system, replaced all the RG58 jumpers between
the repeaters and the RX multicoupler with RG142 double shielded
cable. In order to eliminate the 9913 jumpers between the combiner and
the repeaters, I managed to pull out the combiner input cables to hook
them up directly into the repeaters, all but one channel that for now
remnains unconnected. Even so the interference continued.
So this morning I completely disconnected the combiner from the
repeaters, and hooked one tower antenna directly into CH6 TX, and the
other into CH5 TX. Then I connected the small mobile antenna (just
outside the window) as RX to the RX multicoupler input. Then I
programmed a conventional portable radio so I could transmit on any of
the RX frequencies of the repeaters, so as to try to simulate the same
condition as when a MPT call is placed, the control channel is also on
the air, and the radio that initiated the call is keyed, which is the
condition where the interference comes up.
Now I can manually key up both CH6 and CH5 (with their mikes), and
when I transmit on the portable the interference now DOES come up as
when the MPT call is placed. So this of course rules out any problems
with the Fylde equipment, and I guess also the combiner, as they both
are completely out of the loop. Furthermore I had a helper walk the
portable radio away while I stayed and keyed up both repeaters, it is
interesting to note that I still get the interference while the other
person is at least 300-400Ft away from the equipment rack and keys the
PTT of the portable. Seems that a very strong RF field just in front
of the equipment rack is not really needed to cause the interference.
Remember that I am now receiving with the small mobile antenna, as
both tower antennas are used as TX for CH6 and CH5 repeaters, so the
natural way the signal from the portable can get into the equipment
seems to be trough the mobile RX antenna? or would you still sugge
st that the signal could also be reaching the equipment direcly from
the distance (300-400Ft)?
So maybe the above might point to the preamp, as how else such a
comparatively "weak" signal from the portable radio TX (compared to be
standing just in front of the rack) can cause this interference. My
guess is that there has to be some kind of active amplification
participating in the process so all three carriers (CH5/6 repeaters,
and the portable 300-400ft away) can mix and produce the interference.
So in view of the aparent preamp lead I once again I started inserting
the 6db pad at several places in the RX multicoupler chain, and saw
some slight variation on how many, and which channels where affected.
Then I decided to bypass the preamp altogheter (and turn OFF the
multicoupler power, but I still get some interference (much less) on
some channels. I guess this would definitively rule out the preamp as
a cause. This way the repeater rx is very hard, as the squelch starts
to open up at arround 1uV input signal.
So what else in your opinion could we try? Basically we are now down
to 2 repeaters conected directy to two TX antennas on the tower, and
the mobile antena outside the window used as RX connected to the
multicoupler. All connections between the multicoupler are now made
with RG142, and all the 9913 jumpers are out of the loop. Between the
TX ports of the repeaters, and the 7/8 line that goes to the antenna,
we used two 1/2-inch superflex jumpers.
Any further suggestions and or help would be greatly apreciated.
Thanks for all your help so far.
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