[TowerTalk] Tower "heighth" question

[n4kg@juno.com]

"Optimum" Tower Height  for 10 through 20M  de  N4KG

Ground reflections from horizontally polarized antennas
produce constructive and destructive reflections from
the ground, depending on angle and height, producing
the familiar lobe patterns with peaks and nulls.

Due to the pattern nulls, NO SINGLE HEIGHT will
cover ALL the angles supported by the ionosphere.

The simplest way to fill in the nulls is to use TWO
antennas where the high antenna is 2 to 3 times
the height of the low antenna.   

For the high bands ( 10, 12, 15, 17, 20 meters)
35 to 40 ft will provide coverage up to the highest
angles supported by the ionosphere during daytime
conditions.  This is the "optimum" height for a low
antenna.

Two towers with rotating antennas is a powerful 
conbination.  Alternatively, a lower antenna can
be side mounted on a single tall tower, fixed in
a favorite direction, or rotated using a ring rotor
or a side mounted conventional rotor.

My antenna farm includes a TH7 on a 40 ft tower, 
a TH6 on an 80 ft tower and monobanders for
10M at 32 and 62 ft, 15M at 55 ft, and 20M at 75 ft
on separate towers plus some higher low band antennas
on 7 separate towers.

The 80 ft high TH6 is a good band opener on 15 and 20M
but the lower antennas take over shortly after sunrise. On
10M the TH6 at 80 ft is my WORST performer.

The TH7 at 40 ft is a KILLER to Africa and can often be
my best antenna to Europe when the bands are wide open,
even / especially on 20M in the middle of the day.  With
high sunspots, my  40 ft antennas are sometimes the
best antennas to Japan.

The answer to the question of "optimum" height for the
high bands is that there is NO  SINGLE  HEIGHT that
will be best for all directions on all (high) bands all day
and night.  You can never have enough antennas!

For your proposed 70 ft tower, I would guy it at 35 and
70 ft, stack two tribanders and include something for 40M.  
Force 12 has some interesting new antennas with 40M 
dipoles or 2L40's on the same boom as high band elements.

Alternatively, you could install a heavy duty mast (a whole
separate topic) and stack a 2L40 10 ft above the high tribander.

The boom of a big tribander can also be gamma matched as
a 40M rotary dipole.  I do this for 40 and 30M. GREAT antenna.  

de Tom  N4KG


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