>"kc4ih" <[EMAIL PROTECTED]> wrote:
> After much head scratching I believe that the
> difference in frequency of the pager transmitter
> of 600 khz is the problem
Head scratching doesn't provide real answers. Are
the paging transmitters running circulators? Are
they licensed for the rated power (you'd be surprised
how many are way over their licensed power).
> but have no idea how to solve the problem without
> going to an odd split. The repeater coordinator
> for this area of Virginia won't even consider that
> as an option.
Simple Install and use a parallel aux receiver until
you actually track down the problem(s). Unless you
cause a problem elsewhere, the coordinator can
pound sand.
> The transmitter and receiver on the repeater are
> both Motorola Micor
Are you using a preamplifier? GasFet or Bi-polar
in the receiver section.
> We are running a set of Wacom cavities which were
> bought new and are correctly tuned and the antenna
> is a Phelps-Dodge Stationmaster.
Have you checked the entire system as of late? Reflected
power from the Antenna and the Duplexer. Older antennas
can be problematic. Duplexer plungers do pit and
require checking.
Try a simple DC grounded antenna, mounted low with
known good reflected power (low SWR). Does the problem
go away?
> When the intermod occurs it is dependant on BOTH
> pagers transmitting at the same time. If only one
> pager is transmitting there is no problem.
You will need to find where the mix occurs, location
wise. The hardest part of the job...
> This may at first sound unusual but the pagers are
> in the 150 mhz band and they are exactly 600 kc
> apart. These transmitter are both 250 watts or
> more output.
Got Circulator? or do they have circulators?
> My theory is that the 600 kc (difference of the 2
> pagers) is mixing with the output of the repeater
> 146.64 and producing the 146.04
> signal, the repeater input frequency.
Possible, but not in stone. Never assume a theory
until you've first done the homework.
> We are using sub-audible tone for repeater access and
> as soon as a station working the repeater drops carrier
> the repeater drops. The intermod cannot hold up the
> machine once the tone is removed.
You're lucky, there are cases where the intermod
can hold up the repeater for some time. Lovely
to hear at 3:30 am when you forget to turn the
volume down on the radio in the other room.
> This may be happening in the antenna or hardline
> connectors prior to the cavities. Every test I have
> run, and there have been many, supports this conclusion.
Or your receiver, or someone else's receiver - transmitter
- power amplifier - antenna. The only thing you can first
do is make sure it's not caused by/within your own
equipment.
> We are not the only 2 meter repeater that has fallen
> victim of this problem and in every case we have found
> two pager transmitters situated 600 kc apart near the
> repeater. Most of the other machines have been taken
> off the air, others just put up with it. No one has been
> able to solve the problem and many technicians have
> studied it.
Anyone actually tried anything?
> The searches I have done on Google has turned up
> the stock answer of helical resonators which would
> apply to 2 meter radios but not repeaters.
You might try a High Q Notch Cavity (or cavities) in
the repeater antenna system set to notch at F-center
of the two paging transmitter frequencies.
> If you are familiar with the Micor equipment you
> know that the receiver has excellent helical
> resonators built in.
Which can go right out the window if you're running
some type of receiver preamp. (the wrong way).
After checking your own system first, you need to open
a dialog with the paging companies' technical people
after you first verify they are allowed to run 1/4kw.
> Have any of you ever had this problem and solved it?
> Any input (pun intended) on this matter would be appreciated.
> Ken Sturgill, KC4IH
> Marion VA
> please reply to ([EMAIL PROTECTED])
Get a note book, start writing down what you have and
what you can find out about the paging transmitters.
Do they have Circulators? Do you? Does the mix
go away when your repeater transmitter is terminated
into a load. What type coax jumpers are you using?
Does the mix happen on a different antenna? Is your
antenna dc grounded?
Has the duplexer been checked for Reflected power
and proper adjustment? A nearby lightning strike
can damage the duplexer - receiver - antenna,
yadda... yadda. These are all things you need to
know. You can bet the noise floor of the hill top
can't be great with 500 watts of paging nearby.
Write down everything... keeping track of covered
ground. We'll be here to comment when you get back
to us with your progress.
Good luck
cheers,
skipp
skipp025 at yahoo.com
www.radiowrench.com/sonic
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