Topband: Magic 'T' Combiners

[Tom Rauch]

> If each antenna's input impedance is 50 ohms, and each
feedline is 70.7 ohms
> and an odd number of quarter waves long, each 50 ohms is
transformed to 100
> ohms.  Two 100 ohm loads tied together in parallel is 50
ohms.

.......but if the sources are amplifiers or some other
system or device that is not bilateral in impedance one
device can load the other and cause all sorts of odd
problems.

Say for example you couple two amplified antennas to one
common point in a phased system. The amplifier's impedance
for external signals applied to the output might be pretty
high or low, in which case the impedance terminating the
common point might load the other leg. This can increase IM
products or decrease signal levels.

The same can be true for systems with loss. Systems with
loss don't always (or often) have the same source impedance
as they do load impedance.

73 Tom