Ron,
The WP-641 is barely adequate for a 600 kHz split, and it will let in a
lot of energy from the 144.390 transmitter. I'd try putting two of your
bandpass cavities, tuned to pass 147.690 and with about 1.0 dB insertion
loss, on the input of your repeater, and the remaining bandpass cavity,
tuned to pass 144.390 and with about 1.5 dB insertion loss, on the
144.390 transceiver.
A 2m repeater on 147.090/147.690, with a 50 watt transmitter and a 0.35
uV receiver generally requires about 88 dB of isolation for no desense.
The WP-641 duplexer is rated at 85 dB, but most can manage only 80-83
dB. When you add a 144.390 transmitter to the mix, the desense will
become very obvious. If you are running lower power or have a less
sensitive receiver, the duplexer may have enough isolation- but just
barely.
A bandpass filter on the packet accomplishes two functions: It greatly
reduces the sideband noise that might fall on 147.690, and it provides
densense protection for the packet receiver. Your mileage may vary...
73, Eric Lemmon WB6FLY
Ron Stordahl N5IN wrote:
>
> Have an existing site 147.09 Transmit/ 147.69 Receive site using a 4
> can Wacom WP-641 (uses four 8" cans).
>
> I would like to add APRS on 144.39 receive and transmit (packet).
>
> What I have work with are 3 old DB Products rectangular bandpass
> cavitites (4.5" square by 21" high).
>
> Could I combine these with the WP-641 and achieve adequate
> performance?
>
> Or if I need to round up some better elements to make a usable system
> what would it take? I do have a WP-639 (uses four 5" cans) but I
> would rather not have to use it as I have another application for it.
>
> Ron N5IN
>
>
> Yahoo! Groups Links
>
>
>
>
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