[CQ-Contest] Multiple direction antennas on one radio...why?

[Igor Sokolov]

Danny, Microham stack switch can split into 2 or 3 amp 
http://www.microham.com/index1.html
Then one can split output of each amp into 2 or 3 antenna with anpther stack 
switch.
73, Igor UA9CDC

----- Original Message ----- 
From: <e73m at e73m.com>
To: <cq-contest at contesting.com>
Sent: Thursday, October 20, 2011 5:48 AM
Subject: Re: [CQ-Contest] Multiple direction antennas on one radio...why?


> Update, I found the other place to buy splitters, even for 4 amps,
> http://www.communication-concepts.com/new_page_17.htm
>
> 73 Danny E73M
>
>
> On Wed, 19 Oct 2011 00:30:48 -0400, Tom W8JI wrote:
>> This has my curiousity.....does anyone know what stations doing this
>> really
>> do?
>>
>> When I have a splitter, power divides from the exciter. Each amp has
>> fixed
>> gain. If I have one 10 dB gain amp and a 100 watt exciter I have 1000
>> watts.
>> If I split the power into two 10 dB amplifiers, I have 500 watts per
>> amp
>> minus splitter losses. If I split it four ways, I have less than 250
>> watts
>> per amp. It doesn't matter if I split before the amps or after,
>> except for
>> the size of the splitter.
>>
>> I would either have to have a variable gain amplifier driving the
>> splitter
>> that would increase power into the splitter just over 3 dB  for each
>> two-way
>> split, or I'd have to have dummy loads and replace amplifiers with
>> dummy
>> loads as I pulled antennas out of line.
>>
>> How do they do it?
>>
>> On receiving, summing receive signals from four antennas in different
>> directions would hurt MDS, because at minimum every additional pair
>> of
>> antennas would decrease receiver S/N by at least 3 dB. There would be
>> at
>> least 6 dB of S/N loss and probably more in most cases.
>>
>> Why would someone do that?
>>
>> Or do they really use four radios with four amplifiers and four
>> antennas,
>> and transmit on all and only listen on one???
>>
>> Does anyone actually know how these systems really work, because it
>> seems
>> pretty strange to me on the surface. Are these systems planned, or is
>> a case
>> of just throwing something at the wall and hoping more sticks to the
>> wall
>> than falls off?
>>
>> One way it would work well is with four listening operators on four
>> separate
>> receivers so there is no S/N loss, and one transmitter at a time
>> driving all
>> four amps through one additional amplifier so there is minimal phase
>> distortion if someone hears more than one TX antenna at once.
>>
>> I'm just trying to learn something useful here. I would never think
>> of
>> running four antennas in different directions into one radio for
>> receiving
>> except as a last possible resort.
>>
>> 73 Tom
>>
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