Neal,
The best answer to your question is probably: Whatever works! Both Bill
Lieske of EMR and Len Pringle of Telewave have given me pretty much the
same answer about jumper lengths for duplexers they manufacture.
In most duplexers, the cavities are individually tuned for the desired
insertion loss by adjusting the coupling loops or probes, and each
cavity is tuned for the desired pass loss and notch depth. This is an
iterative process, and eventually the technician has two or three high
pass cavities that are identical, and two or three low pass cavities
that are identical.
At this point the technician selects a test jumper from a rack of
pre-made jumpers that are arranged in 1/2 inch (usually) increments.
>From long experience, he picks one that he knows is close to being the
right length. If each cavity had 0.6 dB insertion loss, he looks for a
jumper that results in about 1.2 dB loss for the pair. If the loss is
more than 1.3 dB, he'll try a shorter or a longer jumper until he finds
one that gives the minimum combined loss. If this is a six-cavity
duplexer, he'll add the third cavity and repeat the process, looking for
about 2.0 dB total loss. If the customer wanted a deeper notch, each
cavity's loops might have been set for a different coupling, which means
that the optimum jumper cable lengths might not be the same. So, the
jumper lengths are not always pre-calculated.
Some duplexer manufacturers have just two or three cable harnesses that
they use for all duplexers in a particular band, and these are
compromises. Sad to say, many commercial installers have no interest in
optimizing their installations, because that effort is time-consuming
and is therefore costly. Hey, if it works, that's good enough! A
purist does not embrace this one-size-fits-all approach!
Regarding jumper cables, they should always be double-shielded; RG-214,
RG-142, or RG-400 are good choices. Do not use RG-58, RG-8, or RG-213
because those are single-shield cables.
73, Eric Lemmon WB6FLY
Neal Newman wrote:
>
> BTW the cans are WP-641's
>
> Neal Newman wrote: Hey Guys.. I am having a problem with my Wacom Cans...
> I am just curious what should the length be for the 4 jumpers.. the 2 between
> the cans and the 2 that meet at the output Tee..... the repeater is on
> 145.230 and what type cable should be used ( I think it's RG-213?) I noticed
> that one cable is teflon... and 2 seem longer than the other 2.. I
> tookmMeasurements.... the jumpers between the cans measure 8.5" and 8.75"
> the 2 jumpers between the cans and the output tee measure 11.77" and 13.5
> "(teflon) I know this is not correct... Serves me right for loaning out the
> cans to friends club for a few years. For some reason I always thought all 4
> cables should be about 13" but I may be wrong... Does anyone know the correct
> length? BTW I measured tip to tip of the pl-259's
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