Just another freindly reminder how important Amateur Radio really is makes
cause for a good argument if anyone questions how its really done.
maybe we should teach the Military how to be Hams & show them how radio
works..
M. H.
----- Original Message -----
From: "Eric Lemmon" <[EMAIL PROTECTED]>
To: <Repeater-Builder@yahoogroups.com>
Sent: Monday, January 03, 2005 10:15 PM
Subject: Re: [Repeater-Builder] Mobile Repeaters- Another Case History
>
> I had planned to sit on the sidelines and enjoy the spirited dialog, but
> Jim brought up a point which needs to be chiseled in stone:
> Communications vans are NOT the ideal environment for a repeater!
>
> Case in point: A nearby Air Force Base has a mobile command post which
> is, for all intents and purposes, a communications van. I invited the
> officer in charge of this vehicle to bring it out to a radio club
> meeting for a "show and tell" to which he readily agreed. It was a
> wonderful experience for the members of my Amateur Radio Club to
> witness, first hand, the superior technology that the communication
> wizards had employed to create this masterpiece of emergency capability.
>
> Our joy at observing this epitome of radio communications capability was
> diminished when one of the hams asked what all of the antennas (UHF
> mobile 3dB gain) lined up, 10 inches apart at the rear of the trailer,
> were used for. The officer replied that each of the antennas was
> connected to a separate Motorola Astro Digital Spectra radio, so that
> multiple conversations could be carried on, using the Base's UHF trunked
> radio system. When asked if two or more conversations had ever been
> handled at one time, the answer was, "Uh, no, for some reason we can
> only talk on one radio at a time." DUH, Hello!?
>
> Rest assured, your local, state, or federal taxpayer dollars are being
> spent for fiascos such as this, simply because these communications
> vans/trailers/command posts are seldom being designed and engineered by
> radio-savvy people, but by catalog browsers and bean-counters. Not only
> is a 10-inch spacing between the antennas of two same-band transceivers
> an invitation to disaster, not to mention potential damage to nearby
> radios, but none of the comm van designers seemed to understand the
> realities of desense and bandpass filtering.
>
> Of course, it is a challenge to install bandpass filters on
> frequency-agile radios, but if you want to operate independently in a
> dense RF environment, you must design your system accordingly. The
> primary channels should be on single-frequency radios, with extremely
> tight bandpass filtering on all receive frequencies and, if necessary,
> on all transmit frequencies.
>
> When properly designed, a communications van/trailer/command post can
> operate simultaneously on a multitude of frequencies, bands, and
> emissions. Unfortunately, far too many such installations are doomed to
> failure before a switch is thrown.
>
> 73, Eric Lemmon WB6FLY
>
> "Jim B." wrote:
>>
>> Running that much power in a communications van *WILL, REPEAT, WILL*,
>> cause interference to other radios in the van, and is TOTALLY
>> UNECESSARY! 10-20 watts is PLENTY for a 'portable' repeater.
>> And in most communcation van environments, there is not enough room for
>> anything the size of a 2M or even a 220 duplexer. A 10 watt UHF repeater
>> in a communcations van with a 3dB gain antenna on 30' to 60' of mast is
>> quite adequate for anything you would need a repeater in a comm-van for.
>> If you need more coverage then that, you need to deploy more then just a
>> comm-van anyway.
>> Of the active comm-vans I am familiar with, only one has a repeater on
>> board, and it never gets used in a response, cause it usually causes
>> more problems then it cures, to the extent that they are thinking of
>> pulling it.
>> --
>> Jim Barbour
>> WD8CHL
>>
>>
>> Yahoo! Groups Links
>>
>>
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> Yahoo! Groups Links
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