cavity to cavity spacing should be an electrical 1/4 wave. So you will need to
know your cables velocity factor to do the calculations. Do not forget to
measure to the center of the "Tee" connector for the lengths. And I was told
that the duplexer to TX/RX should not be a multiple of a 1/4 wave but rather
odd lengths. I remember a Wacom sheet saying that the TX lead should be changed
in length for minimum VSWR. You may want to do some more research.
You will want to use double shielded coax. Such as RG-214 and RG-223. I would
recomend 1/4" Superflex FSJ1-50A if you can find some surplus, A compresion
type BNC connector can be soldered on to it with some modifications with a
dremmel and will save you a boat load on connectors.
Stay away from Braid/Foil coax such as Belden 9913 as this may micro arc and
cause desense. I had some RG-6 (40% braid) on a mountain that was running a
50MHz IF from a microwave reciever. A paging transmitter would turn on and all
the other signals on the mountain would merge and play pac-man in between the
braid and the foil to the point where you could put an antenna of a spectrum
analyzer next to the coax and see a signal increase. I replaced that crap with
Superflex FSJ1-75A (75 Ohm) and the problem has never returned
---------- Original Message ----------------------------------
From: "Jim B." <[EMAIL PROTECTED]>
Reply-To: Repeater-Builder@yahoogroups.com
Date: Mon, 29 Mar 2004 12:49:22 -0500
>Daron J. Wilson wrote:
>
>>>Is there a formula to calculate the cable legnth between duplexer
>>>cans? I find reference to the formula for the cable legnth coming
>>>from the duplexer to the TX-RX, but not between the cans.
>>
>>
>> Where did you find (what is) the formula for jumpers from the duplexer
>> to the transmitter and receiver?
>>
>> N7HQR
>>
>
>...especially since those lengths aren't important.
>
>--
>Jim Barbour
>WD8CHL
>
>
>
>
>
>
>Yahoo! Groups Links
>
>
>
>
>
>
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