My QTH is on the California coast. I use just a wire antenna, so I hear and
speak softly in multiple directions. It's common in contests, especially
after the initial frenzy has passed, for me to hear East Coast or Caribbean
stations who have been exploiting the propagation to EU and have run the
pileups down so that they have to call CQ a lot to pick up new stations.
Frequently I'll hear JA or VK stations calling them, but unsuccessfully -
the East stations are pointing toward EU and apparently don't hear the
Pacific callers.
With better sunspots now, this effect is more pronounced. In the recent
JARTS, 10M was amazing. I had contacts to EU, SA, and ZL over a span of
just a few minutes. If you have a directional antenna, which way do you
point it?
Or... just put up multiple antennas. You may miss some very weak stations,
but you'll probably hear and work more contacts.
A similar situation happens on the TX side. When the supply of new
callers is exhausted, a multi-directional CQ will likely be more effective
in picking up contacts than a directional CQ with just an S-unit or so more
oomph. So you split the power and send it out in many directions.
I'm one of those crazies who enjoy 100W-and-a-wire, so my antenna spreads my
signal around. Or you can put up multiple towers with multiple antennas
and do it that way too.
73,
/Jack de K3FIV
Point Arena, CA
On Oct 19, 2011 5:44 AM, "Tom W8JI" <w8ji@w8ji.com> 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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