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 > > >
