Hi Ian, very informative. I wonder what calc
program you recommend?
This is for Transmit combining at 83 MHz and at
present I am utilising 3/4 wavelength coax (213) from the cavities to the
porcupine.
There is only two transmitters on at present and
the stub somehow likes to be shorter than 1/4 Wavelength.
I'm trying to replicate a system that was
de-commissioned about one year back, and the tech that took over ripped
everything out thinking that he knew better. Originally we were using 6 port
porcupines but he threw these out and I have been fortuitous to even find an 8
port one. All unused ports are left open (Except for TX1, TX2 and the
stub).
We used to run "Star" combining like this in the
old New Zealand Post Office and it worked great!. Just a pity I didn't obtain
some of the site planned and calcs then :-(
Thanks for your help!
_
Gareth Bennett
This e-mail is confidential, if you received this message in error, or
youare not the intended recipient,please return it to the sender and
destroy any copies.Thank you.
- Original Message -
From:
Ian
Ashford
To: Repeater-Builder@yahoogroups.com
Sent: Sunday, November 28, 2004 5:23
AM
Subject: Re: [Repeater-Builder]
Transmitter combiners
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
impedanceis 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
jumper0.85m
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
www.gb3dx.com
- Original Message -
From:
Gareth Bennett
To: Repeater-Builder@yahoogroups.com
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
This e-mail is confidential, if you received
this message in error, or youare not the intended recipient,please
return it to the sender and destroy any copies.Thank
you.
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