> Thanks for your thoughts Jeff, I will answer the questions you posed.
> How close are the respective antennas?
> The problem Paging Antenna and our repeater antenna are
> unfortunately about
> across from each other on opposite legs of the tower. When I
> swap the G-7
> out for the station master I will be up about 20' higher than
> the paging
> antenna.
That will help greatly. As long as you are in each other's aperature, you
will have very little (20-30 dB) of isolation. Once you get the butt of one
antenna above the tip of the other, isolation will increase greatly. Once
you move, you may not have any further problems, but don't count it on it.
> Jeff you stated : "A strong FM signal will create problems.
> The easy and
> cheap fix for that is to put something like a DCI window
> filter or similar
> window filter after the duplexer such that both tx and rx
> frequencies will
> pass". I am not familiar with the term "Window Filter. Is
> this a filter MFG
> by DCI? I am familiar with their site, is there another name
> for Window
> Filter"
> Thanks again Jeff and the group for sharing your expertise.
A window filter is a bandpass filter that, unlike a single-cavity bandpass
filter, passes a range of frequencies (a pass "window") instead of a single
"spot" frequency. The design of the window filter is such that it will pass
a range of frequencies with virtually little difference in attenuation
within the passband; whatever residual variation there is response within
the passband is referred to as passband ripple. A window filter that passes
both your 147.21 tx and 147.81 rx would allow both to pass from the duplexer
to the antenna with little attenuation, yet provide rejection of both the
152 paging tx as well as the 3m FM broadcast signal. The standard DCI
window filters for 2m are comprised of four aperature-coupled helical
resonators. They will custom-make anything you want as well, but you might
as well try just an off-the-shelf 4-pole one to start with (about $100).
Lookee here: www.dci.ca.
--- Jeff
--------------------------------------------
Jeff DePolo WN3A - [EMAIL PROTECTED]
Broadcast and Communications Consultant
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