[CQ-Contest] Multiple direction antennas on one radio...why?
W0MU Mike Fatchett
w0mu at w0mu.com
Wed Oct 19 06:04:31 PDT 2011
I suspect that they are running 4 different 1.5kw or better amps to the
4 antennas. I have no clue which one they might be listening on. Maybe
they didn't realize that listening to 4 at the same time would be a bad
J6/W0MU November 21 - December 1 2011 CQ WW DX CW
W0MU-1 CC Cluster w0mu.net
On 10/18/2011 10:30 PM, Tom W8JI wrote:
> 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
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