[CQ-Contest] Multiple direction antennas on one radio...why?
w8ji at w8ji.com
Tue Oct 18 21:30:48 PDT 2011
This has my curiousity.....does anyone know what stations doing this really
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.
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