The cables not only need to be 100% shielded but should be some sort of
solid dielectric or flexible mini hardline like superflex. Why? The use
of cables like 9913 suffer from hot spots if bent too sharp or tied
tightly with a wire tie. Hot spots are places where the cable does not
conform to it's impedance standard. Solid dielectric cable like RG-214
can be bent fairly sharp and tied without fear of creating this. 9913
also suffers from dissimilar metal construction and is a poor choice in
duplex radio.
Kevin
The Lacko's wrote:
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FYI,
What i have found that work great is to use your monitor and 1 if not
two receivers. I have found that the final tune has such a sharp drop
that a radio on the port and the monitor on high gen gets it right on.
One word of caution make sure all your cables are top notch and 100 %
shielded. I can't tell you how many hours i have spent chasing my tail
because of a bad shield on a connector. Also remember to terminate all
ports during tuning.
Scott
I would like to expound upon this a little.
A while back a gentleman contacted me and warned about the wording
on my suggested duplexer tuning page at:
So I reworded it to allow
some caution, but here is the real skinny.
He suggested that the tuning rod made from Invar (a material that
expands and contracts at the same rate as aluminum) would be
damaged, by the arcing, from tuning the cavity under power and load.
I agree if the cavity is not in resonance, the arcing will be
significant due to the mismatch, however when a cavity is close to
resonance, arcing is minimal.
So...... My suggestion is to use little power if retuning a duplexer
to a new frequency that is more and a few kc's from where it is now
tuned, to get is close, then peak them either for lowest SWR or for
maximum power which ever you prefer with the power you intend to
use.
I use a Yaesu FT-530 handheld and a Bird wattmeter with a 5 watt
slug to get the pass side close. I then use my service monitor (IFR
1200A) and the handie to make the notch close. I then put the
duplexer in line using the cabling I intend to let at the site and
tune the SYSTEM for maximum performance.
I tune for maximum power for solid state equipment, and minimum SWR
in Tube power.
The best way is to have Bird samplers that you can let in place so
as not to change cabling lengths, but I realize not everyone has the
means of doing that.
I have used my GE Mastr Pro / II 4EF5A1 330 watt 2 meter amp into a
set of Wacom WP-641 duplexers in one of my systems for years.
I recheck tuning on the system every 6 months UNDER POWER. I have
never had a duplexer failure due to tuning under power.
If you use your head....and common sense.... there is no problem.
Kevin
Oh yes, One other thing.....
In duplex service.... Tubes are better than transistors.....less
noise.
