Re: Subject: (Fwd) Antenna Diversity

[raf40@oes.amdahl.com (Richard Funnell)]

It's been a while since I looked at such things in detail, but I think you
might have a lot of trouble if you just join the two cables, even if you
properly match the impedance.  Matching impedance will avoid high losses
and reflections, but it won't match phases for you.

The diversity FM units have separate tuner front ends that each receive
separately from one antenna each, then compare strength.  It may be worth
having a switch to allow manual switching between the two cables.

>Note that you have to match impedance when connecting two RF conductors into
>one, so you can't just patch together two antenna cables. Unfortunately, this
>is not a common setup for car radios. If you were trying to split a 75 ohm
>television cable, you wouldn't have any trouble finding an appropriate
>splitter. There must, however, be some circuitry in the head unit that deals
>with this signal diversity issue. Otherwise, you may be feeding in two signals
>at the same frequency that are out of phase. Does someone know if any
>aftermarketeer offers a coax joiner intended for automobile use?
>
>Chris Blumenthal
>'96 A6Q (are they all green?)

Richard Funnell,
San Jose, California
'83 urQ
'87 560 SL