"Richard Clark" wrote in message
...
On Sun, 20 Jan 2008 01:36:22 GMT, "Lee"
wrote:

As your interests span 20 down to 80

Only 20......

and Q intrudes into the bandwidth
you desire at the longer wavelengths, then lowering Q would only drive
down your efficiency and increase your complaint of getting out. It
seems you are rapidly moving away from the loops. You might (if you
can interpret the technical comments) try Arthur's contra-wound
inventions. No doubt, they too would make good receive antennas, and
the proximity of windings would lower Q, but this would come at a
severe loss of gain and sensitivity. A receiver has enough gain to
make up for this loss, but your transmitter is forever crippled with
the introduction of both Ohmic loss and its loss boost due to tightly
coupled currents.

A larger diameter antenna is called for if you are sticking with
loops, but that is probably unmanageable.

20 foot circumference is the longest magloop for 14megs operation!!!
That is with 90% efficiency...

Another breed of loop, the halfwave open loop allows you to build an
omni horizontal polarized antenna in a small area, but we now enter
into other issues you have not discussed. What resources, other than
the tower, are available to you for supporting the linear loaded
dipole you seek?

None

If you have four support points, your garden size is
not unsuited to a full half wave design, there are no Q issues, no
efficiency issues - except for matching to a 5 Ohm load. What can I
say? Compromise antennas demand care and feeding.


All i requested was a suitable design configuration for a linear loaded
halfsize
rotary dipole to go on top of the tower and my reasons why.......
not a discussion on magloops ....

I`ll go with the linear short 1/4 wave vertical layout for each leg of
the
dipole,
where half the element is fed back on itself down to 6 inches from the
ground
( or, in my case, to the mast ) with about 3 inch spacing of the element.

You lost me entirely here. You want a horizontal dipole, and you will
build a closely coupled vertical system that will rotate where half
the element is within 6 inches of ground? Too much is left unsaid in
this description. Is your tower guyed? Freestanding? You are using
the mast (tower?) as half the antenna? Is the mast (tower?) grounded?

This sounds like you are top feeding a vertical quarterwave open
transmission line that rotates around one element. If so, your feed
line is going to really become a nightmare of isolation. It will show
varying horizontal/vertical directivity to a loss of 10dB in any
direction - if you can match to the near short circuit conditions at
the feed point.

I`m not building a vertical !!!

I don't think this is what you mean, but what you describe is vague.

Probably.
Imagine a half wave dipole with each leg folded back on itself
effectively becoming half its original physical length but still
the original electrical length, each leg is like a long thin letter
`U` ..like a folded dipole that has been cut open circuit opposite
the feed point...I shouldn`t have mentioned a vertical because
it mis-lead you, it was meant just to describe the configuration
of the dipole legs.

Cheers.

Len.......G6ZSG.......