> 1. Install as high & as large a top capacitance hat as possible. =
> Spread out losses.
The hat simply serves to make current uniform throughout the
structure. It primarily reduces losses because uniform current
maximizes loop radiation resistance.
> 2. Taller radiators usually yield more radiation resistance & average =
> higher elevation radiation.
Taller structures always yield more radiation resistance all other
things equal. The radiation pattern of a 1/4 wl vertical is not that
much different than that of a very short vertical.
3. Top hat is one plate, ground is the other.
Not if you can help it! If that is the case, the hat must be very close
to ground!
> The closer to ground the = top hat is, the more capacitance.
Within limits of very small changes, unless ratio of hat diameter to
distance to ground is small both physically and in terms of
wavelength, that is true.
> prevent wind damage. 5. Linear loading is virtually lossless, & the
> reverse second (& third) = conductor(s) also radiate.
You must have read some advertisements! Linear loading simply is
a conventional inductor that has a very poor form factor. The loss in
linear loading is higher, for a given conductor size and material,
than a conventional inductor because it takes much more length to
obtain the same reactance.
Linear loading can have the advantage of effectively moving the
loading out on the element, if it is properly implemented. If
improperly done (as is often the case) it can have the effect of
moving loading lower, and making radiation resistance decrease.
6. It is easy to
> add an aluminum tubing "whip" to the beams mast at 65 = ft, for total of
> 95 ft physical height. 7. Whip will survive winds alone, but not with any
> form of capacitance = hat at its top.
The whip will do almost nothing if the tower is many times thicker
than the whip and especially if the tower has any capacitance at
the top.
> The theory of operation is that the beam will exhibit much more =
> capacitance with the earth, at its lower mounted position, & draw more =
> current up higher into the whip/wire area where I want more radiation. =
> Current reaching the top & descending back down the whip to the top hat =
> beam should add even more high radiation in linear loading fashion.
Radiation will simply cancel out while adding loss resistance.
Why would you elevate the feed and ground system? That only
complicates matters and shortens the antennas effective height,
and you would gain nothing at all over a conventional system using
a decent ground.
There is very little "free lunch" or magic to antennas. The most
efficient vertical would be one as tall as you could make the
**current area**, with a good ground system and a conventional
feed and loading system. A large hat helps make current uniform,
so the inductor can be placed anywhere in the system without
affecting radiation resistance or current distribution.
Think of the problem as ampere-feet of distance, with the
capacitance as the terminating point. Even if you run a wire above
the capacitance and back down, the ampere-feet is only the
distance from ground to the hat!!!
73, Tom W8JI
W8JI@contesting.com
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