Is there any optimum height for a 3ft dia magloop, or is it dependent on
frequency??.

I have mine planted in the lawn with the top about 6ft from the ground (on a
rotator!)
and was curious whether to work it against ground or put it at the top of
the tower,
or have i completely lost the plot???, Heh heh........

Surprising how cheaply a magloop can be built for and after 12 months it
still works well!!.

Thanks.....

Lee.......G6ZSG.....

"Lee" wrote in
o.uk:

Is there any optimum height for a 3ft dia magloop, or is it dependent
on frequency??.

I have mine planted in the lawn with the top about 6ft from the ground
(on a rotator!)
and was curious whether to work it against ground or put it at the top
of the tower,
or have i completely lost the plot???, Heh heh........

Surprising how cheaply a magloop can be built for and after 12 months
it still works well!!.

What band is yours on? I have a 55-inch diameter coax loop that I'm using
on 75, but I'm seriously thinking of working up a multiband design in soft-
drawn 3/4" copper pipe. It would be six feet in diameter (mainly due to
space considerations).


--
Dave Oldridge+
ICQ 1800667

"Lee" wrote in message
o.uk...
Is there any optimum height for a 3ft dia magloop, or is it
dependent on
frequency??.

I have mine planted in the lawn with the top about 6ft from the
ground (on a
rotator!)
and was curious whether to work it against ground or put it at the
top of
the tower,
or have i completely lost the plot???, Heh heh........

Surprising how cheaply a magloop can be built for and after 12
months it
still works well!!.

Thanks.....

Lee.......G6ZSG.....

=========================================
Lee,

There is no optimum height for a magloop.

Loss induced in the ground reduces as height above ground increases.

When the height of the bottom of the loop is more than the loop
diameter, loss in the ground can be considered negligible.

This is modelled in program MAGLOOP4 which can be downloaded from the
website below and run immediately.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

"Dave Oldridge" wrote in message
9...
"Lee" wrote in
o.uk:

Is there any optimum height for a 3ft dia magloop, or is it
dependent
on frequency??.

I have mine planted in the lawn with the top about 6ft from the
ground
(on a rotator!)
and was curious whether to work it against ground or put it at the
top
of the tower,
or have i completely lost the plot???, Heh heh........

Surprising how cheaply a magloop can be built for and after 12
months
it still works well!!.

What band is yours on? I have a 55-inch diameter coax loop that I'm
using
on 75, but I'm seriously thinking of working up a multiband design
in soft-
drawn 3/4" copper pipe. It would be six feet in diameter (mainly
due to
space considerations).

Dave Oldridge+
ICQ 1800667
========================================
Dave,

Magloops with copper pipes are the most efficient of all small
antennas.

They should be rotateable through about 45 degrees.

Changing from coax loop to 3/4" or 1" copper pipe loop will be a
considerable improvement on both transmit and receive. Especially if
it is not too low above ground and is not in a cluttered environment.
The idea is to keep ground loss less than conductor loss.

For multi-band operation you will be best with a motor-driven vaccuum
tuning capacitor. With a 1000pF capacitor and a small loop the 160, 80
and 40m bands can be covered. It depends on the minimum capacitor
setting and loop perimeter.

There is no noticeable difference between aluminium alloy and copper
pipe. Aluminium alloy is lighter in weight and stands up to the
weather better but is more difficult to bend.

A square loop is not noticeably worse in performance than a circular
loop and may be easier to construct.

Download program MAGLOOP4 from my website. It may provide food for
thought.
----
Reg, G4FGQ.

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
:


"Dave Oldridge" wrote in message
9...
"Lee" wrote in
o.uk:

Is there any optimum height for a 3ft dia magloop, or is it
dependent
on frequency??.

I have mine planted in the lawn with the top about 6ft from the
ground
(on a rotator!)
and was curious whether to work it against ground or put it at the
top
of the tower,
or have i completely lost the plot???, Heh heh........

Surprising how cheaply a magloop can be built for and after 12
months
it still works well!!.

What band is yours on? I have a 55-inch diameter coax loop that I'm
using
on 75, but I'm seriously thinking of working up a multiband design
in soft-
drawn 3/4" copper pipe. It would be six feet in diameter (mainly
due to
space considerations).

Dave Oldridge+
ICQ 1800667
========================================
Dave,

Magloops with copper pipes are the most efficient of all small
antennas.

They should be rotateable through about 45 degrees.

Changing from coax loop to 3/4" or 1" copper pipe loop will be a
considerable improvement on both transmit and receive. Especially if
it is not too low above ground and is not in a cluttered environment.
The idea is to keep ground loss less than conductor loss.

Actually, considering the costs, I'm thinking perhaps just 1/2 inch pipe.
I did some modelling and the difference between 1/2 inch and 2 inch pipe
is really only 6db and I can get nice flexible 1/2 inch pipe.

For multi-band operation you will be best with a motor-driven vaccuum
tuning capacitor. With a 1000pF capacitor and a small loop the 160, 80
and 40m bands can be covered. It depends on the minimum capacitor
setting and loop perimeter.

I'm thinking more on the lines of switching capacitors in and out. I
also don't care if the feedpoint SWR goes up fairly high, as long as my
tuner can flatten it. I can make some pretty good fixed capacitors from
heliax.

There is no noticeable difference between aluminium alloy and copper
pipe. Aluminium alloy is lighter in weight and stands up to the
weather better but is more difficult to bend.

A square loop is not noticeably worse in performance than a circular
loop and may be easier to construct.

This is true given equal areas.

Download program MAGLOOP4 from my website. It may provide food for
thought.

I have it, thanks. I also have a spreadsheet that I made up that does
all the calculations for copper loops.

--
Dave Oldridge+
ICQ 1800667