[TowerTalk] Combining antennas - My experiences

[Robert Shohet]

Hi Guys,

I have 4 stacks of HG105CA's and HG155CA's on the same tower at my QTH.  The
spacing is somewhat unconventional
but optimized for my wildly variable terrain on rock ledge.   My
observations are probably going to be different from most but they
might shed some more light on this discussion.  I have noticed that
generally these observations are true whether it is 10 OR 15, but 15 seems
to have "sharper" distinctions in antenna combos to EU than 10.  However, as
far as JA and the deep pacific are concerned, 10 is more widely variable
between antenna combos, especially late at night in the Winter..

First, although the BEST combination of any two or three antennas, at any
given moment,  is likely to be equal to or slightly
better than a single antenna, this is often NOT the case!

I have found that when the band is first opening to EU, the top antenna by
itself is FAR SUPERIOR to any combination
of antennas.  Having said that, when the solar flux is very high and there
are VERY LOW A & K indices  with VERY LOW levels of aurora (usually 1 or 2)
often the lowest antenna is the loudest and superior to any other
combination of antennas.  For in-between wave angles, it is truly a mixed
bag and CONSTANTLY changing, often on a minute to minute basis.  It also
depends on what stations you are trying to work.  For example....

My single HG155CA at 90' maybe the BEST antenna to UA3 at NOON in winter
even as it is 20 db down to Western Central EU
(I,DL, etc.) at that exact moment!

The more disturbed conditions are, the greater the likelihood that the TOP
antenna will be superior to all other antenna combinations
regardless of what time of day it is or where the calling stations are.

Many other times, adding a second or third antenna in phase doesn't increase
the signal strength of the guys calling me, but it does "smooth out" their
signals so there is less QSB and more "angle coverage".

All this is changing all the time depending on solar flux, time of year,
time of day, time of cycle, A & K indices, auroral oval and many other
factors.  I am CONSTANTLY changing antenna combos as I operate a DX contest.
Most of the time the best combo of antennas is a combo of TWO antennas,
rather than 3 or 4.

>Bill (W4ZV) and others, my recollection of W3LPL's presentations on
stacking, at the Dayton Antenna Forum and elsewhere, was that the stack was
always equal or better than any individual antenna.  I think this was for
two-stacks, like 50/100' on 20, 45/90' on 15 and 35/70' on 10, and the
parameter may have included from Maryland to Europe, not sure about that
one.  What's your experience?  73 - Rich, KE3Q

NOW, onto W4ZV's most interesting comment on backscatter.....

   >        Pete, my experience has been fairly good with pointing
  my 10m 3-stack at mostly orthogonal angles, but sometimes
  you get some very strange results...especially for backscatter
  signals.  Quite often, I would hear a weak station, and then
  switch to the single antenna in that direction, only to have
  the signal totally vanish.

YES!  I have noticed this for years!  Each year that I have operated the 10
meter contest, before the band REALLY opens to the West Coast, I hear the
West coast FAR BETTER with my HG105CA at 23' pointed NORTHEAST!  I can move
any of my higher antennas and point them at the West coast and I CAN NOT
HEAR THEM!  But the one at 23' pointed at the Atlantic hears them quite well
and that is how I work them!  When the band really opens later, I CAN NOT
hear the West Coast on the 23' antenna, except about 40 db down.

I have NEVER understood why this happens, or why the difference between 23'
and 37' is so critical (my next higher antenna), but it is.  So what do I do
about it?  Each year when I would run EU in the morning in the 10 Meter
contest, I would make sure to phase in the 23' antenna which would allow me
to work the West Coast via backscatter, even through it dropped the signal
strengths of the EU stations by about a few DB..

Ah, the charms and challenges of 10 meter propagation!

>       The other variable in this is knowing which antenna
  height is best for different target areas at different times of
  day.  You can get a feel for that with VOACAP but there is
  probably no substitute for experience.

There is definitely no substitute for experience.  Each QTH is unique and
different and different again depending on where you are in the sunspot
cycle.  And each band is a separate entity unto itself and TOTALLY
different!

73
Bob KQ2M