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

Tom W8JI w8ji at w8ji.com
Thu Oct 20 17:52:09 PDT 2011

> I assume that having antennas simultaneously pointed in four directions
> means that they have transmit gain in all four directions, although that
> would suffer a bit if you have all four amps cranked back to 1/4 legal
> power.  I suspect it would be awkward to readjust all amps for those
> times when propagation is clearly dead for one or more of those
> directions, assuming they couldn't afford to waste transmit power.

They would automatically crank back and up with an exciter into a splitter. 
Do a two-way, and each amp probably gets -3.5 dB drive. Do a 4 way, and it 
is -6.5 or so per amp. Do a 3-way, and it is either all -4.9 dB or one -3.5 
and two -6.5.

This assumes some reasonable loss.

> Having four antennas simultaneously pointed in four directions
> sacrifices the S/N you would otherwise have with just one antenna, but I
> assume that it does give you the ability to at least hear callers that
> would otherwise be off the back or side of a single yagi without having
> to switch antennas to do so.

That's what I assume also, but with stereo or separate RX's and ops nothing 
would be lost.

> I think can understand simultaneously using more than one antenna.
> What I cannot understand, assuming total power output meets all rules,
> is how using multiple amplifiers simultaneously to do so is not
> considerably more expensive, slower, and operationally awkward than
> simply feeding a single amplifier into a high power splitter as is
> commonly done with stacks or 4-squares.

Six of one, half dozen of the other. Split in front, drive reduced by the 
split. Split after, output to port reduced by split.

I'm not judging things one way or another, because I have no idea what 
anyone does. I'm just curious what people do. Seems like a waste of 
amplifiers to me, but who knows what people do.

The only thing that interests me is the advanced switching technology some 
people use. Very professional in a few cases. The replies, which there are 
too many to respond to, ran the course from a T connector up to some very 
fancy home made switching stuff. It looks like a common thing, to use 
multiple directions.

73 Tom 

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