At 08:48 PM 7/5/2005, Mathew Quaife wrote:
>Ok, the situation is that my repeater is being heard by commercial
>aircraft on 132.950 Mhz.
Ouch! BTDT, with a kenwood synthesized transmitter that didn't
detect out of lock properly.
I had to pull the plug till it was resolved.
>I've looked at the transmitter on the SA, there is one small spur
>there, but this same spur is there if I use just an ht, or any other
>radio for that matter. This is hooking it to the repeater antenna
>directly, or through the duplexer's. My question is, could it be
>something in the antenna system, or where might I look.
What I did to fix this, was to first realign the synth so the PLL was in lock.
Then I added a coax stub filter on the transmitter output, cut to be
an odd 1/4 wave multiple at 121.1 (where my problem was) and an even
number of 1/4 wavelenghts at 146.730, where our carrier should
be. The stub got me 40dB of supression, and the retune got rid of it
entirely, so even if it happens again, the stub assures that the
tower will not be hearing from us.
Ideally, tune the stub with an SA and tracking generator, so you can
be sure the pass and stop are where they should be.
I also made two spares when I made mine, and labeled it so some well
meaning guy years in the future dosen't remove "that useless hunk of coax".
The planes hearing it more than the tower was also the case here, it
just happens that they frequently overfly the repeater site.
> The transmitter is the Maggorie Hi Pro EV1 and
>the amplifier is a Vocom 200 watt amp. 90 Watts is what is being fed
>to the antenna from the duplexer.
Crystal or synth transmitter? If xtal, does the problem show up on
(your transmit freq - the crystal freq)?
Could be hopping in and out of an overtone mode, maybe a failing
crystal, or bad component in the osc itself.
My experience with the local tower folks was very good. No heated
tempers, and they even complimented us to the FCC about how quickly
and well we resolved the problem.
The funny thing was, this has always been an example I used in talks
as a "nightmare scenario" of what could happen...
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