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

Tom W8JI 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.

73 Tom 

More information about the CQ-Contest mailing list