On Sun, 20 Jan 2008 01:36:22 GMT, "Lee"
wrote:

I don`t want a fixed dipole at low height!! i want a rotary dipole on the
top
of my tower (mast)....i am aware i can fit a 33foot fixed, wire dipole into
a
35foot garden, lengthwise, but the length of my garden runs east/west so the
dipole would fire north/south - not good...... the magloops receive very
well,
with lower noise than a regular antenna, i can hear stations i wouldn`t
normally
hear on a regular antenna, plus, a horizontal dipole, generally, has more
gain
than a horizontal omni magloop at the same height but is a noisier r/x than
the
magloop, which makes the dipole better for t/x mode....Yes?...

Hi Len,

Yes, but marginally. This is a double edged sword. The Q that gives
you such superlative receive characteristics is going to drive you
into CW mode in, perhaps, 80M, and certainly in 160M - not to speak of
the critical tuning. You have the height, something I missed from the
distraction of 20 other unrelated postings to this thread, so you have
solutions and that height is both far and away sufficient for the
upper HF, and more to the matter, the best practical solution for your
neighborhood. As to the antenna construction, you have answered the
Ohmic losses to a considerable extent, and you are aware of the
relationship of Ohmic Loss to Radiation Resistance. You would do well
to report to the group your SWR bandwidth for several of these bands
so we can get a grasp of the actual Q. Simply for 160/80/40/20, how
many KHz between the 2:1 points?

There are a lot of pluses there, except for the high Q on low bands.
You also express in your list of negatives that you don't seem to get
out (a transmit problem).

My garden is 14ft wide and a 14meg dipole is 33ft+, i don`t want my
neighbours
complaining when half the antenna is over their garden when i`m working east
west...hence linear loading the dipole...to shorten it!!

If I recall (as you have a lot of widely separate issues here), you
want to operate 20M. Your garden as you state here is too narrow (it
is) for the direction you desire. An efficient design is going to
demand end loading aka top hat style (long radial spokes at the end of
each arm of the dipole you want).The end loads, if sufficiently
developed (and not a simple installation, I suspect) could do it
without further loading with a coil somewhere (and if it were
anywhere, the good advice from years of reporting here would indicate
that it would be one half to two thirds out and away from the feed
point, on both sides). Another alternative is an inverted V which
would seem to be within your capacity (depends on where the tower is
sited).

As your interests span 20 down to 80 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.

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

73's
Richard Clark, KB7QHC