I have a pdf copy of the Moto Diplex Manual. If it s needed
I can upload it somewhere.
73, Dick, W1KSZ
-Original Message-
From: skipp025 skipp...@yahoo.com
Sent: Aug 23, 2010 12:49 PM
To: Repeater-Builder@yahoogroups.com
Subject: [Repeater-Builder] Re: Motorola Diplex Antenna Manual
Re: Motorola Diplex Antenna Manual
Scott Zimmerman wrote:
I would LOVE to know some of the theory behind
this method. I was hoping to use this on a remote
base antenna with 'Station' type antennas, but I
don't think that will work since it clearly states
that Only standard base-loaded antennas are used
Looks like a straight forward scheme to isolate two ports
with odd wave-length coax stubs. The paper says only one
of the stubs may be extended an extra half wave-length.
I suspect the restriction to base loaded coils forces each
of the antenna feed points to retain in forced physical
hardware something close to their (hopefully) 50 ohm drive
impedance at the F-center tuned frequency. That relatively
low Z value would hopefully be 1/4 line transformed into a
relatively high Z (impedance) value back at the T-Connector.
Some type of ensured feed-point decoupling requirement might
be involved/required.
Comments? Suggestions? Theory?
I think we went through that already...
men...@... men...@... wrote:
The Motorola document is based on the use of the Spectrun
base loaded antennas sold by Mother. The Spectrum antenna
is a series coil arrangement, not a shunt fed or tapped
coil; this is very important!
I don't remember seeing any paperwork on the Spectrum Base
Loaded Antennas... Out here on the west coast, Mother is
a Cookie Company (with decent but hard Oatmeal cookies).
I would expect the series coil antenna to be something similar
to a 3/4 wave or electrically shortened antenna system and the
shunt/tapped coils to be more 1/2 and 5/8 wave. Why would a
series coil antenna be a requirement?
The chart works quite well for the Spectrum antennas and
will probably work for any other series fed LB coil. It
will not work for any antenna that is shunt fed as myself
and several others found out when trying to make two
non-Motorola antennas work on a fire engine.
On Low Band with Utility Vehicles, I've found a number of
reasons why certain low band antennas don't work well. Depends
on each situation and I've recently had an install where only
a shunt fed antenna would work.
The maker of the Untenna antennas told me once that they
could be combined in the same way but the method was different;
IIRC the antenna to T cables were to be quarterwaves but
were for the opposing frequency. Never tried it and that
was a long time ago and no notes to back up my memory.
Another document exists that details using a ball mount
full length whip and a Spectrum series fed LB base load
in the same shared configuration.
Milt
N3LTQ
Quickly looking at a Spectrum Antenna data sheet, I might
suspect they are trying to simulate/emulate/achieve a no
ground plane halve-wave operation for proper feed-line
decoupling.
got to go, back later...
s.
Yahoo! Groups Links
