Error correction :

They need be rotateable only through about 90 (ninety) degrees.

This is to ensure an antenna can always be directed towards maximum
signal even when there are 3 or 4 plastic guy ropes from the top of
the loop which can prevent a complete rotation.
----
Reg, G4FGQ.

Does it matter if the remotely tuned capacitor is at the top or the bottom
of the loop?

"Reg Edwards" wrote in message
...
Error correction :

They need be rotateable only through about 90 (ninety) degrees.

This is to ensure an antenna can always be directed towards maximum
signal even when there are 3 or 4 plastic guy ropes from the top of
the loop which can prevent a complete rotation.
----
Reg, G4FGQ.

As far as an "optimum" height, it seems that a loop oriented such that
it lies in a vertical plane, such as the one you have and Reg is
describing is not going to perform better as you change the height,
once you're far up enough to eliminate ground return losses. In fact,
my little toy EZNEC model at 14Mhz with a 4' loop shows the development
of high angle lobes if you increase the height of a vertical-plane
magloop.

Seems though that if you oriented the loop such that it was in a
horizontal plane and put it at a good "DX height", up where a dipole
would start to give good low angle radiation, you would get an
omnidirectional azimuth pattern but the elevation pattern more like a
dipole at that height. This could be advantageous if you have a high
support.

So if you're down at 3.5MHz or something, loop in the vertical plane
near the ground is the way to go, as you'd not likely be able to get
the loop up high in terms of wavelengths.

Seems, though, if you had a 20m (1 wavelength @ 14MHz) high tower with
low windload capability and wanted to put up a horizontal-plane loop
for 14MHz, you'd get more gain at low angles than a near-ground-mounted
vertical-plane loop.

It's analogous to the situation with a ground mounted vertical vs. a
high dipole. The ground mounted vertical has better low angle
radiation than a low dipole, but not better than that of a high dipole,
and leads to the usual situation of verticals for the low bands and
horizontal antennas for the high bands.

this comment over normal soil, if you've got sal****er, pse
disregard :-)

73,
Dan
N3OX

Does it matter if the remotely tuned capacitor is at the top or the
bottom
of the loop?

========================================
In principle, it doesn't matter.

But it is important the capacitor is located diametrically opposite to
whatever arrangements there are to feed the loop.

Ideally the loop should, as far as possible, be isolated and be
allowed to find its own electric balance with respect to ground.

The capacitor itself is likely to be unbalanced with respect to
ground. So it it is better to place it as far as possible from the
ground and everthing else, i.e., at the top. The highest voltages are
concentrated at the ends of the loop connected to the capacitor.

It is best NOT to connect the main loop to the feedline. Use a small
coupling loop in the same plane as the main loop and about 1/5 of the
diameter if the coax is 50-ohms. For 75-ohm coax it is about 1/4 of
the diameter.

Isolating the main loop from the coupling loop and feedline prevents
RF current from finding its way on to the feedline.

If the capacitor motor is not very well isolated from the capacitor
itself then place an RF choke in the bunch of control wires near to
the motor. Bring the control wires down from the motor across the
loop diameter and in a neutral electric field. Anything which comes
down vertically across the diameter is in a neutral field. It could be
a metal mast to support the motor and, via the motor, the top of the
loop itself.

In general, having the capacitor at the bottom of the main loop is
more likely to unbalnce the capacitance of the loop to ground.
----
Reg, G4FGQ.

Thank you, Reg, for your comments. They are especially relevant for the
project I am currently working on.

John, N9JG

"Reg Edwards" wrote in message
...
Does it matter if the remotely tuned capacitor is at the top or the
bottom
of the loop?

========================================
In principle, it doesn't matter.

But it is important the capacitor is located diametrically opposite to
whatever arrangements there are to feed the loop.

Ideally the loop should, as far as possible, be isolated and be
allowed to find its own electric balance with respect to ground.

The capacitor itself is likely to be unbalanced with respect to
ground. So it it is better to place it as far as possible from the
ground and everthing else, i.e., at the top. The highest voltages are
concentrated at the ends of the loop connected to the capacitor.

It is best NOT to connect the main loop to the feedline. Use a small
coupling loop in the same plane as the main loop and about 1/5 of the
diameter if the coax is 50-ohms. For 75-ohm coax it is about 1/4 of
the diameter.

Isolating the main loop from the coupling loop and feedline prevents
RF current from finding its way on to the feedline.

If the capacitor motor is not very well isolated from the capacitor
itself then place an RF choke in the bunch of control wires near to
the motor. Bring the control wires down from the motor across the
loop diameter and in a neutral electric field. Anything which comes
down vertically across the diameter is in a neutral field. It could be
a metal mast to support the motor and, via the motor, the top of the
loop itself.

In general, having the capacitor at the bottom of the main loop is
more likely to unbalnce the capacitance of the loop to ground.
----
Reg, G4FGQ.

"Reg Edwards" wrote in
:

Error correction :

They need be rotateable only through about 90 (ninety) degrees.

This is to ensure an antenna can always be directed towards maximum
signal even when there are 3 or 4 plastic guy ropes from the top of
the loop which can prevent a complete rotation

Rotation is probably not an option here as it has to sit on an apartment
balcony. There will be some ground clutter, too, from the balcony railing.
But that may not be as debilitating as it looks because the whole business
is 10m up and any currents in the aluminum balcony railing tend to add to
the radiation, though the pattern can become moot.


--
Dave Oldridge+
ICQ 1800667