[TowerTalk] Takeoff angles - some practical experience

[Robert Shohet]

This topic has already been covered extensively from the theoretical and
scientific viewpoints.  I am somewhat lacking in those areas but I thought
it might be helpful for me to share some of my  observations strictly from
the standpoint of a contester who has extensively guest-operated (and from
home in the past three years) with all different kinds of antenna systems
from all over the Northeast in all different contests for the past 20+
years.

First, there are no absolutes.  Propagation is three dimensional
(vertical/horizontal radiation plus shapes of the lobes).  It is also
affected by changes in the ionosphere (which is varying second by second) ,
which in turn is affected by time of day, time of year, time of cycle, sun
"stuff", etc.    THEN, you have the effects of antennas which of course
depend on design, height, stacking (or not), phasing (or not), feedline
losses, radiation efficiency, etc.  Then of course there is terrain.  And
finally, there is the awareness and intervention of the operator, equipment
and of course, other activity on the band.

In other words, there is an INFINITE number of possible permutations which
vary second by second for a given qth, operator and equipment modified
further by all the above.  So much for uniform observations and absolute
statements!  Now for the practical.....

At every location there are "magic" heights, these being the height(s) at
which a good antenna, properly built and installed seem to cover most of the
angles, most of the time, even when logic dictates otherwise.  This magic
height will vary depending on ionospheric changes and the current "place" in
the sunspot cycle since the angles at which the desired signals are
propagated will also change, higher antennas generally more useful at the
bottom of the cycle and lower antennas more useful at the top of the cycle.
Having said that, I have found through the personal experience of operating
more than 200 DX contests at all different stations and station locations,
that hill-top locations seem to have LESS difference between antenna
combinations than over flat ground.  I have also noticed that higher
antennas at hill-top locations seem to suffer less vs low antennas with
high-angle condx than the differences over level ground.  I will confine my
observations to Europe.

Many times in the past two years, my top 10 & 15 were superior most of the
weekend to all signals vs the lower antennas or combinations.  This is not
uniform.  The higher antennas always opened and closed the band and in
between, generally as the MUF rose (and I stayed on a given band)
progressively lower antenna combos in-turn became superior and the opposite
as the MUF dropped,  though (less than 1% of the time) was the lowest
antenna by itself, superior.  In between, the "best" antenna combo
CONSTANTLY changed every few minutes, sometimes even every few seconds.
Since I have a WX0B stackmatch and 4 identical antennas on 10 and 15, I am
CONSTANTLY listening and changing the antenna combo as necessary.  Often
what is best at 1300z in down an s-unit or two at 1305z, 1310z etc.  Cndx
are ALWAYS changing. Sometimes in the middle of an opening, the highest
antenna, becomes, best, sometimes the lowest.  The other thing I can be
certain of, is that it is CONSTANTLY changing and the differences between
antennas 2 & 3 vs 3 & 4 can be 1 - 2 s-units in a matter of 10 seconds!
This is NORMAL!

If you have the "proper" stacking distances between antennas (generally 22'
on 10M, 31' on 15M and 43' on 20) you will see even MORE pronounced
differences, again, MODIFIED by QTH and your proximity to the desired area
of signal.

During an opening, usually the further away stations are louder on the lower
angle (higher) antennas.  For example, at 1300Z with really good cndx it is
common to see DL's peaking on the 15 meter 30' & 60' antennas and  UA3's
louder on the 60'/90' antennas.  A VQ9 might be louder still on the 90' or
109' antennas.  Likewise an EA could be several s-units down on the top
antenna and might actually be loudest on the 30' by itself.  Of course we
are NOT talking about disturbed propagation where SOMETIMES the lowest
antenna is best or sometimes the highest antenna is the only things that
"hears".  We are also not talking about ionospheric ducting, sporadic E,
Transequatorial (TE) skip, aurora or meteor scatter, all things that blow
conventional "logic" to hell.  We have been "blessed" by all the above in
the past few months in CQWWSSB, CQWWCW, ARRL10,   complicating matters even
more, where on in the ARRL 10M contest on Saturday I made most of the EU
qso;s on the 45/70' stack in the morning, most on the 22/45' stack in the
afternoon and then EVERYTHING on the 100' footer on Sunday.

Then you get top of the cycle phenomena where 20 "opens" to EU in late
afternoon with the 43' antenna and works its way UP in height  as darkness
approaches - same with 40 meters.

A really interesting Northeast phenomena is the JA path with good cndx,
where in the late afternoon on 15 in the Spring, at my qth in SW CT 15 miles
from the NY border, JA peaks at about 15 degrees (NOT the usual 335!) on the
109' antenna, about 0 degrees on the 60' antenna and 340 degrees on the 30'
antenna.  This is not unusual either.  Since phasing antennas changes the
wave angles, sometimes I then have to rotate the antenna AFTER I stack
different antennas!

You can also see this on 15 with EU during the 10M contest. Sometimes the
high antenna (low angle) path is skewed to the North or South with the high
antenna and less skewed or not at all with the low antennas.

The bottom line is that there are NO absolutes.  Anyone is best served by
having multiple antennas at multiple heights and the ability to phase any of
them at any time.  It is even better if you can have OTHER types of
radiators as well like a 4-sq, single vertical, delta loop, inv v etc.

Although there are some weekends where high antennas are predominantly
better (usually with lower SF and a higher level of geomagnetic disturbance)
and some weekends where low antennas shine it is ALWAYS best to have
available combinations of antennas and keep an open mind about what "should"
work best.  Also keep in mind that the same antennas in the midst of the
prairie DO NOT behave the same way as on the edge of a cliff, or in a
valley, even if the antennas and stations are the same and only a 1/4 mile
apart!

Height generally makes MORE openings possible, more often and for a longer
period of time and gives you the chance to experience weird propagation
paths and phenomena that are just "not there" with lower antennas.

The more operating experience one has at more and more locations, the more
one realizes that no one antenna is best and the "best " antenna height will
vary based on so many factors.  The only thing that matters is what is
likely to be best for the particular weekend you want to operate a given
contest!

One final note...  I have found that from my location and many others you
can NOT be "too high" to South America.  Often a 150' antenna hears better
into ZP, LU, HK, Ce, etc. than a 40' or 100' antenna regardless of cndx.  I
still don't understand why this is.  Maybe one of the more knowledgeable
guys on this reflector can explain it to me.

73 & may you have all the "right" heights!

Bob KQ2M





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