I am in the planning stage for a 160 meters compact loop antenna. A loop
antenna may not have metal nearby, so I am planning to use a wooden pole to
support the top of the loop. In the ARRL Antenna handbook, it states that
"W5QJR made a pole of 2 x 4-inch lumber with 1 x 4-inch boards on either
side to form an I section. He held the boards together with 1/4-inch bolts,
2 feet apart and tied rope guys to the top. This made an excellent mast up
to 50 feet high."

Does anyone have any comments on the feasibility of an unguyed pole using
this same type of construction? Naturally, a portion of the pole would have
to be underground, and perhaps set in concrete. What about a 50 feet pole,
with 10 feet underground ,which would give you a 40 foot mast?

An alternative would be to have a contractor install a 40 feet utility pole,
but I assume the wooden pole described above would be less of an eyesore (to
the neighbors) than a utility pole.

Any comments and advice will be appreciated.
John, N9JG

A vertical conductor, a metal tube, running diametrically across a
large magloop with the tuning capacitor at the top, has no effect
either on radiating efficiency or the radiation pattern. It may as
well not be there apart from providing a prop or support for the
antenna itself. It will, of course, need to be well-insulated from the
high-voltage parts.

In general, provided the longest dimension of foreign metalwork is
much less than 1/2-wavelength, and there is not much of it, negligible
loss will be induced in it. This is due to the very low loss
resistance of most metals.

Metalwork in the vicinity of beam antennas may upset only the
radiation pattern.

Short lengths of foreign metalwork in close vicinity of tramsmission
lines, such as open-wire and ladder lines, will cause neglible loss
but will slightly reduce the line impedance Zo which might affect the
L and C settings of the tuner.

But beware of "semi-conductors", like damp wood such as foliage and
tree trunks, in the near-fields of antennas and lines. Their higher
impedance provide a better power match to the 'generator'.

You can have as much foreign polyethylene as you like.
----
Reg.

This is useful information to know. I don't know why the section about small
loops in the Antenna Handbook doesn't mention this. BTW, how far does the
near-field extend?

"Reg Edwards" wrote in message
...
A vertical conductor, a metal tube, running diametrically across a
large magloop with the tuning capacitor at the top, has no effect
either on radiating efficiency or the radiation pattern. It may as
well not be there apart from providing a prop or support for the
antenna itself. It will, of course, need to be well-insulated from the
high-voltage parts.

In general, provided the longest dimension of foreign metalwork is
much less than 1/2-wavelength, and there is not much of it, negligible
loss will be induced in it. This is due to the very low loss
resistance of most metals.

Metalwork in the vicinity of beam antennas may upset only the
radiation pattern.

Short lengths of foreign metalwork in close vicinity of tramsmission
lines, such as open-wire and ladder lines, will cause neglible loss
but will slightly reduce the line impedance Zo which might affect the
L and C settings of the tuner.

But beware of "semi-conductors", like damp wood such as foliage and
tree trunks, in the near-fields of antennas and lines. Their higher
impedance provide a better power match to the 'generator'.

You can have as much foreign polyethylene as you like.
----
Reg.

"John N9JG" wrote
This is useful information to know. I don't know why the section
about small
loops in the Antenna Handbook doesn't mention this. BTW, how far
does the
near-field extend?

======================================

It's because neither the authors nor the editors were aware of it.

The near-field on the surface of an antenna's conductors starts off at
a very high value. The far-field is zero at zero distance.

The near-field fades into the distance just the same as the
ar-field - only much faster. It also has a radiation pattern which
depends on an antenna's structure.

For argument's sake, for an isotropic antenna (which doesn't exist),
at a distance of 1/2/Pi = 1/6 of a wavelength from the antenna, the
near-fields and far-fields are equal to each other but differ in
phase. They both exist together and their effects on foreign bodies
are inseparable from a measurements point of view. They exist
seperately at all distances only as a mathematical fiction.

The near-field of open-wire transmission lines is sensibly zero at a
distance of 4 or 5 times the wire spacing but the radiation field is
finite and very small. The radiation field increases with wire spacing
and is a maximum when spacing is about 1/2-wavelength which nobody
ever uses. This accounts for the lack of use of low-loss open-wire
lines at UHF and higher frequencies.

Back to Magloops where the measurement unit is loop diameter rather
than wavelength and the near-field is mainly magnetic. The magnetic
field falls off at a rate proportional to the cube of distance. I
would be very happy with a distance of 1/2 the loop diameter or more
between the loop and large foreign bodies such as the ground.

Highly conductive metallic bodies merely slightly detune the loop with
little additional loss.
----
Reg.

"John N9JG" wrote in message
...
I am in the planning stage for a 160 meters compact loop antenna. A loop
antenna may not have metal nearby, so I am planning to use a wooden pole to
support the top of the loop. In the ARRL Antenna handbook, it states that
"W5QJR made a pole of 2 x 4-inch lumber with 1 x 4-inch boards on either
side to form an I section. He held the boards together with 1/4-inch bolts,
2 feet apart and tied rope guys to the top. This made an excellent mast up
to 50 feet high."

Does anyone have any comments on the feasibility of an unguyed pole using
this same type of construction? Naturally, a portion of the pole would
have to be underground, and perhaps set in concrete. What about a 50 feet
pole, with 10 feet underground ,which would give you a 40 foot mast?

An alternative would be to have a contractor install a 40 feet utility
pole, but I assume the wooden pole described above would be less of an
eyesore (to the neighbors) than a utility pole.

Any comments and advice will be appreciated.
John, N9JG

If you really want to have the "mast" unsupported, consider a 50-60'
telephone pole
properly installed (for your type of soil) with one end buried deeply.
Perhaps you could
use a fiberglass extension from its top to support the antenna.

It would be worth your while to have a mechanical engineer calculate your
design's survival
characteristics in high wind and compare it with 100 year records for high
wind speed. Also you
might consider the prospect of icing if you live in a northern climb -- I
assume that the mast
is at a corner of the loop.
Regards,
Ed, N5EI

A wooden utility pole with a length of 40 feet above ground would do the job
for me. It's just that I am not sure how the neighbors would react. A search
of the web did show that there are fiber glass flag poles available that
have sufficient height, but I don't know if they can support the weight of
100 feet of 3/4 in copper pipe and a 10-15 lb remotely tuned capacitor
inside a weather-proof box.

"Edward A. Feustel" wrote in message
...

"John N9JG" wrote in message
...
I am in the planning stage for a 160 meters compact loop antenna. A loop
antenna may not have metal nearby, so I am planning to use a wooden pole
to support the top of the loop. In the ARRL Antenna handbook, it states
that "W5QJR made a pole of 2 x 4-inch lumber with 1 x 4-inch boards on
either side to form an I section. He held the boards together with
1/4-inch bolts, 2 feet apart and tied rope guys to the top. This made an
excellent mast up to 50 feet high."

Does anyone have any comments on the feasibility of an unguyed pole using
this same type of construction? Naturally, a portion of the pole would
have to be underground, and perhaps set in concrete. What about a 50 feet
pole, with 10 feet underground ,which would give you a 40 foot mast?

An alternative would be to have a contractor install a 40 feet utility
pole, but I assume the wooden pole described above would be less of an
eyesore (to the neighbors) than a utility pole.

Any comments and advice will be appreciated.
John, N9JG

If you really want to have the "mast" unsupported, consider a 50-60'
telephone pole
properly installed (for your type of soil) with one end buried deeply.
Perhaps you could
use a fiberglass extension from its top to support the antenna.

It would be worth your while to have a mechanical engineer calculate your
design's survival
characteristics in high wind and compare it with 100 year records for high
wind speed. Also you
might consider the prospect of icing if you live in a northern climb -- I
assume that the mast
is at a corner of the loop.
Regards,
Ed, N5EI

"John N9JG" wrote in message
...
A wooden utility pole with a length of 40 feet above ground would do the
job for me. It's just that I am not sure how the neighbors would react. A
search of the web did show that there are fiber glass flag poles available
that have sufficient height, but I don't know if they can support the
weight of 100 feet of 3/4 in copper pipe and a 10-15 lb remotely tuned
capacitor inside a weather-proof box.

"Edward A. Feustel" wrote in message
...

"John N9JG" wrote in message
...
I am in the planning stage for a 160 meters compact loop antenna. A loop
antenna may not have metal nearby, so I am planning to use a wooden pole
to support the top of the loop. In the ARRL Antenna handbook, it states
that "W5QJR made a pole of 2 x 4-inch lumber with 1 x 4-inch boards on
either side to form an I section. He held the boards together with
1/4-inch bolts, 2 feet apart and tied rope guys to the top. This made an
excellent mast up to 50 feet high."

Does anyone have any comments on the feasibility of an unguyed pole
using this same type of construction? Naturally, a portion of the pole
would have to be underground, and perhaps set in concrete. What about a
50 feet pole, with 10 feet underground ,which would give you a 40 foot
mast?

An alternative would be to have a contractor install a 40 feet utility
pole, but I assume the wooden pole described above would be less of an
eyesore (to the neighbors) than a utility pole.

Any comments and advice will be appreciated.
John, N9JG

If you really want to have the "mast" unsupported, consider a 50-60'
telephone pole
properly installed (for your type of soil) with one end buried deeply.
Perhaps you could
use a fiberglass extension from its top to support the antenna.

It would be worth your while to have a mechanical engineer calculate your
design's survival
characteristics in high wind and compare it with 100 year records for
high wind speed. Also you
might consider the prospect of icing if you live in a northern climb -- I
assume that the mast
is at a corner of the loop.
Regards,
Ed, N5EI



John,
Would you be able to provide additional support from the bottom of the loop
to ground?
That might relieve the situation. Could you have the feed at the bottom
rather than at the top and
could the box be supported?

If you could support from the bottom and use a heavy walled copper pipe
which would provide
substantial rigidity, the fiberglass might work.

I suspect that the neighbors are not going to be enthusiastic about the
loop.
Regards,
Ed, N5EI

Thanks, Ed, for your comments. Yes, If I have a supporting pole in the lawn,
there is no reason why I couldn't also have a support directly below the
loop. The loop would be in the shape of an octagon, it would be fed through
either a 1/5 size coupling loop or a gamma match at the center of the bottom
side, and the series resonating tuning capacitor would be inserted at the
center of the top side.

The 3/4 inch copper pipe would be the same type that is used inside houses
and is quite rigid. I can not seem to find, by Goggling, the weight of
copper pipe. By going to the local Lowe's store and hefting a 10 feet length
of pipe, I estimate the weight of 10 feet of pipe as being somewhere in the
range of 1-3 lb.

"Edward A. Feustel" wrote in message
...

"John N9JG" wrote in message
...
A wooden utility pole with a length of 40 feet above ground would do the
job for me. It's just that I am not sure how the neighbors would react. A
search of the web did show that there are fiber glass flag poles available
that have sufficient height, but I don't know if they can support the
weight of 100 feet of 3/4 in copper pipe and a 10-15 lb remotely tuned
capacitor inside a weather-proof box.

John,
Would you be able to provide additional support from the bottom of the
loop to ground?
That might relieve the situation. Could you have the feed at the bottom
rather than at the top and
could the box be supported?

If you could support from the bottom and use a heavy walled copper pipe
which would provide
substantial rigidity, the fiberglass might work.

I suspect that the neighbors are not going to be enthusiastic about the
loop.
Regards,
Ed, N5EI

My Lowe's store sells two kinds of copper pipe. The less costly one is
harder, lighter and thinner. I began my antenna experients with the huskier
stuff and after it bent, replaced it with the thin material, which is
holding up OK so far.

The thinner material seems to have about the same weight per foot as
aluminum. I'm using copper instead of aluminum because it is easier to make
good electrical connections between the pieces.

Tom

"John N9JG" wrote in message
...
Thanks, Ed, for your comments. Yes, If I have a supporting pole in the
lawn,
there is no reason why I couldn't also have a support directly below the
loop. The loop would be in the shape of an octagon, it would be fed
through
either a 1/5 size coupling loop or a gamma match at the center of the
bottom
side, and the series resonating tuning capacitor would be inserted at the
center of the top side.

The 3/4 inch copper pipe would be the same type that is used inside houses
and is quite rigid. I can not seem to find, by Goggling, the weight of
copper pipe. By going to the local Lowe's store and hefting a 10 feet
length
of pipe, I estimate the weight of 10 feet of pipe as being somewhere in
the
range of 1-3 lb.

"Edward A. Feustel" wrote in message
...

"John N9JG" wrote in message
...
A wooden utility pole with a length of 40 feet above ground would do the
job for me. It's just that I am not sure how the neighbors would react.
A
search of the web did show that there are fiber glass flag poles
available
that have sufficient height, but I don't know if they can support the
weight of 100 feet of 3/4 in copper pipe and a 10-15 lb remotely tuned
capacitor inside a weather-proof box.

John,
Would you be able to provide additional support from the bottom of the
loop to ground?
That might relieve the situation. Could you have the feed at the bottom
rather than at the top and
could the box be supported?

If you could support from the bottom and use a heavy walled copper pipe
which would provide
substantial rigidity, the fiberglass might work.

I suspect that the neighbors are not going to be enthusiastic about the
loop.
Regards,
Ed, N5EI

John,

The general rule-of-thumb for a utility pole installation in sort-of normal
soil is 10 percent of the pole's length, plus 2 feet in the ground. For
example, a 40 foot pole would be placed in an augered hole 6 feet deep,
leaving 34 feet above ground. The hole should be back-filled and tamped to
provide support for the pole. No concrete is needed.

73, Larry - W1GOR


"John N9JG" wrote in message
...
I am in the planning stage for a 160 meters compact loop antenna. A loop
antenna may not have metal nearby, so I am planning to use a wooden pole to
support the top of the loop. In the ARRL Antenna handbook, it states that
"W5QJR made a pole of 2 x 4-inch lumber with 1 x 4-inch boards on either
side to form an I section. He held the boards together with 1/4-inch bolts,
2 feet apart and tied rope guys to the top. This made an excellent mast up
to 50 feet high."

Does anyone have any comments on the feasibility of an unguyed pole using
this same type of construction? Naturally, a portion of the pole would
have to be underground, and perhaps set in concrete. What about a 50 feet
pole, with 10 feet underground ,which would give you a 40 foot mast?

An alternative would be to have a contractor install a 40 feet utility
pole, but I assume the wooden pole described above would be less of an
eyesore (to the neighbors) than a utility pole.

Any comments and advice will be appreciated.
John, N9JG