Gary,
Before a solution can be discussed, you need to define the problem.
Connect a spectrum analyzer to the end of the hardline and determine the
frequencies and relative amplitudes of the signals you see. You may
discover that your receiver is being desensitized by a harmonic or other
spurious emission from another transmitter at the site. If this is the
case, the owner of the offending transmitter has the responsibility to
fix the problem.
It is also possible that intermodulation is occurring, either due to
problems at the site, or within your own receiver. Such problems can be
a bear to resolve.
My gut feeling is that one or more notch filters may be part of the
solution. You can only do so much with bandpass filters; when you have
very powerful transmitters that are close- such as the 101.5 MHz signal-
a very sharp notch cavity may be needed for each one. That's why I
suggest using a spectrum analyzer to identify what it is you have to
notch out. You might be able to create some effective notch filters
with quarter-wave lengths of 7/8" or 1.25" hardline.
There's also the possibility that some inexperienced technician has left
the shields off a UHF station, and its exciter (which is normally a VHF
exciter followed by a tripler) is radiating a signal close to your image
frequency. Spurious signals originating in the equipment building may
become much more pervasive when the victim's feedline is not properly
grounded.
Finally, keep in mind that paging systems frequently use backhaul or
control links in the 72-76 MHz band. If such a link is at your site, it
probably has a ferrite isolator to protect it from other transmitters.
Such a device requires a harmonic filter to block the second harmonic,
which will be in the 144-152 MHz band. Hmmm...
73, Eric Lemmon WB6FLY
[EMAIL PROTECTED] wrote:
>
> A question to all you repeater guru's out there. Have a repeater in a high
> noise environment at a large TV tower site. Lots of pagers, FM transmitters, 2
> ways, etc on this tower. My Super Stationmaster 2 meter antenna is just 5
> feet
> away from a bed spring style 45 kw FM transmitter on 101.5 MHz. My repeater
> is a Canadian mobile Micor along with Wacom duplexer and a circulator on Tx
> side. Have a DB 4062 cavity can tuned to bandpass Rx between duplexer and
> receiver. Works OK but the 1000 feet of 7/8 hard line has a great effect on
> the Rx
> side of the repeater. Also a new paging tenant might be blanking the Rx out
> of my repeater. Putting the repeater at the base of the antenna is not
> possible. I would like to improve the receive side of the repeater. Have the
> following
> equipment available:
> Advanced Receiver Pre amp GaAsFET P144VDG
> Telewave TWPC-1005-1 pass cavity 88 - 108 mhz
> DB 4062 WC-B 143-156 mhz 6 can duplexer
> Wacom 641 duplexer 4 can (second set)
> Kay switchable attenuator pad
> DCI bandpass 144-148 filter
> DB 4048 cavity cans (2) from disassembled duplexer
> What would be the best choice and hook up to increase the Rx sensitivity and
> keep the noise out of the receiver? Any help would be really appreciated.
> Gary K2UQ
>
>
> Yahoo! Groups Links
>
>
>
>
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