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

Tom W8JI w8ji at w8ji.com
Thu Oct 20 07:31:03 PDT 2011

It looks like this is a popular thing to do. I was considering it myself 
using the DX Engineering stacking system because one system could be adapted 
to do power ratio division between antennas pretty easy, plus flips phase.

I personally, because my antennas do not have the same perfect SWR, would 
not have a magic T system. The magic T would dissipate a portion of the 
imbalance for no good reason, because I would not care about antenna to 
antenna isolation at all anyway. They are not active devices, like PA 
stages, where there can be mixing.

I've received dozens of private e-mails describing other systems from very 
good (where receivers as selected to antennas, or are in stereo, or have 
multiple ops) to just what works. It looks like some people have put a great 
deal of thought into this for optimizing the system for maximum benefit, but 
even those who don't optimize seem to like the system.

I used to use, many years ago, a system on 20 meters for normal operating 
that used a groundplane antenna above my 5 element Yagi. I did this because 
if I transmitted on the Yagi, Florida retired hams would talk to north USA 
hams even if I was on a frequency long before they came on. I received on 
the beam, and when QRM got bad switched to the vertical for transmit.

There are similar problems on 160 in contests, and other bands, where a 
tight TX pattern results in others ignoring the existing use and they start 
up. This causes a loss of a run because of QRM, and the obvious solutions 
are only two... to leave the frequency or to go wide pattern on transmit and 
narrow on receive.

It appears most people do this legally, simply using one PA into multiple 
antennas. Multiple PA's make little sense to me, because phase is not 
controlled. I looked at an FM broadcast years ago that was convinced two 
antenna on two transmitters gave them better fill. What they gained in some 
areas they lost in others, and where they lost would move around and change 
size depending on temperature changes and PA tuning.

Maybe the people running four antennas with no control of phase and 
direction are shooting themselves in the foot anyway?

Thanks for the replies, and it is very interesting to see the wide range of 
thought and science that goes into building a better station. Some of the 
custom equipment is very professionally done, and appears to be perfectly 
legal and moral.

73 Tom 

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