It should also be clarified that this is the major difference
between a hybrid ferrite combiner and a cavity combiner. The hybrid can be
used with any freq's in the specified band, no matter how close spaced (
technically 2 transmitters on the same freq is ok) , but at the cost of
major power insertion with large channel capacity... Cavity combiners are
substantially less loss however the freq spacing needs to exceed 150khz
between channels to get reasonably better performance....even then cavity
versions are going to be on the order of 5-6db IL on channels in a 10
channel config. ( Theory vs real world performance)
Real power loss on a hybrid combiner is more like 4db per 2 port/channel
coupling, as opposed to 3db, so IL is going to be higher than the
theoretical losses.
Doug
KD8B
At 10:48 AM 8/5/2005, you wrote:
>Tom Saunders wrote:
>
> >>about 55% of each transmitter's
> >>output gets burned up in a dummy load, each time two signals are
> >>combined. Thus, eight 100 watt repeaters combined into one antenna will
> >>have about 11 watts at the antenna.
> >
> >
> > While it is true that aprox. 50% of the power from each transmitter is
> > lost in the combiner, the remaining 50% gets thru. So a 100 watt
> > transmitter will send 50 watts out to the transmission line. 50 * 8 =
> > 400w total.
>
>No-doesn't work like that. For every two transmitters you combine, you
>have ~3dB loss. So for 4 tx's, you have 6 dB loss, and for 8 tx's, you
>have 9 dB loss. (Barring of course hardware differences that will move
>those maybe a dB either way.)
>So for 8 100W tx's, the theory gives you 12.5 W to the bottom of the
>coax per channel. And other factors will likely add up to yield the 11W
>that was mentioned.
>--
>Jim Barbour
>WD8CHL
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