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

Rudy Bakalov r_bakalov at yahoo.com
Fri Oct 21 03:56:39 PDT 2011


Another point to consider is that having an amp for each antenna allows you to use off the shelf components, such as coax, switches, baluns, etc.  compared to custom or not so common 10 KW rated ones. It is not only cheaper, but also makes it possible to have spares that are readily available.

Although I have not crunched the numbers, I suspect that it might be cheaper to buy 2 x AL-1500s than a single OM3500. Thus, price plus all the other benefits make it an attractive value proposition.

Rudy N2WQ

On Oct 20, 2011, at 8:52 PM, "Tom W8JI" <w8ji at w8ji.com> wrote:

>> 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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