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Gareth,
For two transmitters the length of the circulator
to porcupine jumper would be 5/8 wavelength in coax.
When these two are parrelled the common
impedance is 25+j25 ohm.
Looking at the Smith chart it looks like a
paralleled s/c stub of -j25 would acheive a match to 50 ohm.
Putting these figures into lengths of
RG213:
Circulator to porcupine
jumper 0.85m
s/c stub 0.58m
I dont know how many transmitters you are
combining,the stub impedance is -j16ohm for 3 transmitters and -j12 for
four.
There are lots of good transmission line
calculators available on a google search.
Ian
G8PWE
----- Original Message -----
Sent: Saturday, November 27, 2004 4:11
AM
Subject: [Repeater-Builder] Transmitter
combiners
Hi there Group :-)
Is there somebody in the group
who has knowledge on "Star" transmitter combining? I am trying to remember the
formula for the "Tuning Stub" that also is fitted to the star, or "Porcupine"
as we call them over here. All the stubs here are less than 1/4 wavelength
(Including VF of cable) and as normal are shorted at the end :-)
..
Everything else is as one
would expect with the food chain going like this...
Transmitter-Isolator-Cavity-"Porcupine" - Antenna.
I want to tune this as best as
I can, but don't want to spend large amounts of time hacking off coax
:-)
Any formula would be
appreciated. I have tried to reverse engineer what we have in service to gain
some formula, but nothing makes sense.
Can anybody remember?
Thanks in advance :-)
_________________________________________________________________
Gareth Bennett
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