[TowerTalk] What about hams with small lots???

[n4kg@juno.com]

Here are some more recommendations for small lots.

First, remember that it is NOT necessary to use 80%
guying distances.  80% is a carry-over recommendation
based on maximizing the load capacity at the full rated 
height of the tower.  Note that the Rohn Foldover
tower data sheet shows a guy anchor spacing of 
only 18 ft for a 48 foot R25 foldover and 25 ft for
a 58 ft foldover.  Yes, closer spacing increases
the vertical load on the tower, but shorter towers
don't have as many guys as taller towers so you
can trade off total height for anchor distance. 
The shorter the tower, the closer the anchors
may be place without overloading the tower.
Personally, I would not go under 50% of the
tower height but it can be done in extreme
cases.  DO THE MATH.  If the loads are
near the maximum ratings of the tower or
guys, you can go to R45 and 1/4 inch guys
for added strength.  Self supporting towers
are another solution.

There seems to be a feeling that DIPOLES
are not particularly good antennas and they
tend to be lumped in with other inferior solutions.
This is a MISCONCEPTION.

DIPOLES are highly efficient radiators when
placed 1/2 wavelengths or more above ground.
Remember, the dipole is the basis for all Yagi
antennas.  

Inverted Vees are NOT as effective as a straight
horizontal dipole.  One of the touted properties
of inverted vee antennas is that they offer some
radiation off the ends.  This energy must come
from somewhere.  The end radiation is subtracted
from the broadside radiation.  The steeper the
apex angle, the less the radiation broadside to
the wire.  For a 90 degree apex angle, I believe
the broadside radiation is reduced by up to 3 dB.
Check it out on your modeling program.

Simple *horizontal* dipoles can be constructed on aluminum
tubing and appropriate insulators or even wire on bamboo or
fiberglass poles.  These can be rotated with a small TV rotor.
Another option is to use two dipoles at right angles to each
other for fast direction switching and NO rotor.  Small antennas
are usually less expensive than rotors.  Turning antennas 
wastes time and energy in contests.  I like having LOTS of
fixed antennas covering all of the principal target areas for
contesting.  Two rotary antennas can be "parked" on different
target areas and moved as propagation changes from 
EU to JA and S.A. to South Pacific.

Some examples of horizontal rigid dipoles are 
the Cushcraft D3 or D4, Force 12, Mosley TA-31 
(or DE from a TA33).  HyGain driven elements
can be remounted as stand alone dipoles.

On the Low Bands where an inverted vee may
not be entirely above 1/2 WL high, additional
ground losses are incurred by the ends being
in closer proximity to earth.  The obvious 
advantage of an inverted vee is that it only requires
one support.  It is still better than a vertical antenna
on the high bands.  Verticals with GOOD ground
systems are effective radiators on the Low Bands.

Horizontally polarized Delta Loops are also good
radiators for limited space if sufficient height is
available.  With a 60 degree apex angle, limited
real estate is needed to pull out the bottom corners.  
Gain loss from the sharp apex angle is compensated
for by the addition of the lower halfwave which acts
as a stacked configuration of bent half waves.  For
best results, place the *bottom* wire at least 30 ft
(preferably 40 ft) high for 10 through 20 meters.

Contrary to popular opinion, the BEST way to improve 
your signal from a small lot is to use an AMPLIFIER.  

Remember, a GOOD Full Size 3L Yagi optimized for gain 
is only 5 to 6 dB over a (horizontal) dipole at the same height.  

A Full Size 2L Yagi is typically 4 to 5 dB better than a 
(horizontal) dipole at the same height.  Trapped or other
compromised Yagi's have even less gain and bandwidth.

To realize a 6 dB improvement over a 100 W transceiver
it is only necessary to increase power output to 400W.
Used amplifiers in the 500 to 800W range can be provide
7 to 9 dB power gain respectively, on ALL bands, and can
be purchased for a few hundred dollars.  Amplifiers in the
1000 to 1200 W range provide 10 to 11 dB power gain
and are still reasonably priced compared to full legal limit
(and above) amplifiers based on expensive ceramic tubes.
The full legal limit of 1500W is under 12 dB and even
2KW is only 13 dB over 100W, making that last dB 
or two very expensive.

de  Tom  N4KG






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