Thanks for the feedback and general comments... Very informative and good to
have the topic kicked around a bit.
As mentioned previously I inherited a TX combiner on a radio site that has
just grown without any planning and thought involved. There are 5x
transmitters from 151.5 through to 153.025 with the closest TX to TX spacing
being 250 KHz.
I have seen star combiners that have been fitted with shorted stubs that
"Appears" to be in the vicinity of around 1/8 wavelength... I was hoping
that there was some theory or maths to get close to this length.
In the past I have maintained TX star combiners where the combiner
itself has been made for a selective frequency band, with capacitive disks
inside. (These almost always had shorted stubs fitted to a spare star port).
I understand the theory of an odd wavelength from the cavity to the
combiner (Usually 3/4 wavelength) But would like to know more theory and if
possible the maths that go into proper transmitter combining.
Thanks again for reading :-)
_________________________________________________________________
Gareth Bennett
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please return it to the sender and destroy any copies.
Thank you.
----- Original Message -----
From: "skipp025" <[EMAIL PROTECTED]>
To: <Repeater-Builder@yahoogroups.com>
Sent: Tuesday, May 02, 2006 6:04 AM
Subject: [Repeater-Builder] Re: Transmitter combining and Multicoupling
information.
> > "Harold Farrenkopf" <[EMAIL PROTECTED]> wrote:
> > Easiest way to verify the actual length required is to
> > remove the loop from the can (or adjust it for minimal
> > coupling) and put it in the star with a cable of
> > approximately the correct length and use 2 of the other
> > star ports to measure the resonant frequency of the loop
> > and cable to see if it is in the mid of your frequency
> > spread.
>
> Much of the time, the "mid frequency" is not the most
> desired location. I'm not sure if you'd actually call or
> spec the cable/loop combo as a "resonant frequency"
> element... although most people might call it one.
>
> > All the cables would then be the same length to the
> > star if the loops are the same.
>
> Not in all cases... also depend on the number of legs
> in use via the star or equiv device. Also the frequency
> spread...
>
> > The open stub would be close to the electrical 1/2 wavelength if
> > required to make the output return loss symmetrical and better. I
> > personally usually do not use a stub and try to make the cables work
> > alone but then again, I am using an Agilent 8753ES network analyser
> > that makes the job very easy. The stub is used if the frequency span
> > is larger or the cables used are not the ideal lengths.
> >
> > The open circuit stub is trimmed to make the return
> > loss symmetrical.
> > Harold
> >
>
> I've found the shorted stub used most often, Not only as a
> trap, but as a much desired (in most cases) dc shunt.
>
> I've seen star combiner setups with various caps and or stubs
> networks on the unused ports.
>
> Telewave sells a square box type - star, which I think is
> real crap. I like the Sinclair Star mucho betta'.
>
> cheers,
> skipp
>
>
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
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