LF: Re: 5 port combiner transfer function ?

["James Moritz" <james.moritz@btopenworld.com>]

Dear Graham, LF Group,

...>
2    ports      50  ohms      load
2    ports    power  input     50 ohm
1    port    power  out      50 ohm

Is  the  power  out  simply   i/p 1 + i/p2  =   o/p ??
...>
No... The output is only the sum of the inputs if *all* the inputs of the 
combiner are the same amplitude, and have the correct phase relationship 
(which might be 0, 180 degrees or phase quadrature, depending on the type of 
combiner). Roughly speaking, the difference between the input signals will 
be dissipated by the combiner. I think in this case (but you will have to 
check yourself ;-)), if the 2 driven inputs are equal, the output power will 
be the total input power -3dB (and a bit of insertion loss), i.e. the same 
as each input signal. If the two inputs are different signals, I think each 
input would be attenuated by 6dB at the combined output. This would 
therefore not be helpful as a way of combining the outputs of 2 PAs, but it 
would be OK as a way of combining two signal generator outputs to produce a 
two-tone signal, for example.
Cheers, Jim Moritz
73 de M0BMU