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