> "Harold Farrenkopf" <[EMAIL PROTECTED]> wrote:
> > > There are 5x transmitters from 151.5 through to 153.025
> > > with the closest TX to TX spacing being 250 KHz.
> >
> > .... which borders on almost being too close for a Star layout.
> > Unless the bottles are large and high Q, those two legs prob.
> > have a lot of loss.
>
> No, 250kHz is fine for a 5 TX star combiner (with isolators and or
> more pass cans in series). 10" cans can go down to 60khz.
Depends on what you consider usable performance. I'm not fond
of >4dB loss right out of the starting gate in addition to all
the other gremlins, which tend to pop up in marginal combiner
operation. Yes, the Q of the cans make a big difference as
well as the number of... but many of the common combiners are
single can and a bunch are even reduced size bottles.
> Sinclair's stubs are near open half waves if my memory serves
> me and are adjusted (trimmed) to present a balance return loss
> across the span of frequencies used.
Sinclair's Engineering is first rate work. Another applied stub
method is always interesting to learn about.
> > More often 1/4 wave cable lenghts in the popular 4 port (less
> > than or equal to) combiners when size and cable lengths permit.
>
> 5 way will require the 3/4 wave version to get to 5 cavities
> from the star.
In many cases yes, but I have seen "folded" versions of combiners
where 5 way starrs were used with 1/4 wave cables. The 1/4 wave
cable lengths seem to be easier to match.
> I was a systems guy and never got into those details.
I'm a moderate Republican not so happy with the way my current
Politcal Party trys to operate. .
> Look at manufacturer's catalog pictures to see how they
> do TX star combiners.
Catalogs can be very helpful.
> The loop and cable length presented approximately a 1/4 wave
> or 3/4 wave shorted stub when you look at it through the star
> with a tracking generator and spectrum analyser.
> The resonance I mentioned was a minimal insertion loss or
> the best VSWR (best return loss) at the middle of your
> frequencies)
The fly in the soup is the minimal insertion loss is not
always in/at the middle of the selected frequencies. And
the return loss or resonant curve/value is not a uniform
shape.
cheers,
skipp
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