Paul,
I have tuned three Q-202G duplexers in the past six months, and all
wound up with nearly identical performance. The only difference between
a Q-202G duplexer for the 2m band and one for the 150-174 MHz band is
the length of the jumper cables. The factory-made harness for the
commercial band measures 12" between the cavities and between the inside
cavities and the antenna tee connector. The 2m harness measures 14" for
these four sections. The measurements are between the centers of each
tee connector. The physical size of the cans and the coupling loops are
the same for both splits.
Using a network analyzer and great care to match the return loss between
cavities, I was able to achieve at least 86 dB of isolation at 1.5 dB
insertion loss. This is barely adequate for a solid-state 35W repeater
that has 0.35 uV sensitivity at 12 dB SINAD. If you're willing to
accept some impairment due to desense, you can run more power-
especially if you have a tube PA. A 100W repeater normally requires 100
dB of isolation for zero desense, and that usually calls for six
cavities. However, I have used a Q-202G duplexer with two added
bandpass cavities on the receive side, and it had zero desense with a
100W PA.
73, Eric Lemmon WB6FLY
Paul Holm wrote:
>
> Has anyone had luck using the Q-202G duplexers in the 145-148 range? What
> needs to be done with them for use in the ham band? Just different cables?
> What sort of isolation figure is possible? Thanks.
>
> Paul
>
>
> Yahoo! Groups Links
>
>
>
>
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