On Tue, 10 Jan 2006 23:53:50 -0500, "J. Mc Laughlin"
wrote:

However, when mobile stations are sent by the control channel off to one
of the allocated frequencies, problems seem to occur with the digitally
encoded voice signals. Since systems that use a total of one transmitting
site do not appear to suffer and systems that use multiple transmitting
sites do suffer, one hypothecates reasons.

A form of multipath distortion exists that is due to the use of
multiple, well spaced transmitters that are transmitting at the same time.
That is the type of distortion I called "multiple-transmitter-multipath."

Multiple site Motorola systems don't transmit on the same frequency
from different sites. In theory what you say is true (although it's
not "multipath", it's plain old simple interference - multipath refers
to a signal from a single transmitter arriving over multiple paths,
and nothing else), but if you look at the actual in-the-field sites,
you'll see that your theory isn't put into practice.

One might guess that if one is close to one of the transmitters (of a
multiple transmitter system) then one would not have a problems because the
near transmitter's emissions would dominate. I have not tested this
hypothesis.

It's not an hypothesis, it's called "capture effect", and it's a
property of FM receivers.

When listening to a one transmitter site (Owosso), my BCD396T receives
almost all voice signals well most of the time. When listening to a system
(APCO25) that uses multiple transmitting sites (Genesee), my BCD396T
produces distorted audio much of the time.

Genesee is *a* site - in a larger system that encompasses many sites..
The fact that it lists more than 1 control frequency doesn't mean that
it has multiple control channel transmitters on the air at the same
time.

At my location, the signal from
the control channel of the multiple transmitter system is somewhat stronger
than the signal from the one transmitter system.

Since there's only 1 control transmitter on any one frequency at any
one time for any one site, you're analyzing the situation incorrectly.
You may be getting interference of some sort, but it's not due to
multiple control channel transmitters from the same system at the same
location.

In short: multipath can be caused by means other than signal
reflections

Except that what you're describing isn't called multipath. Multipath
is the term used to refer to signals from a single transmitter
arriving over multiple paths - hence "multi-path".