i've been considering an antenna for the audio frequency range plus 1 to 20
hz. basically a big coil would work.

i've thought about using a steel drum, but i don't have room for that in my
new QTH. mu metal rods would be very expensive, even ferrite would be
expensive for an 100,000 turn antenna.

not sure what to use. maybe steel core.

Gravity

gravity wrote:
i've been considering an antenna for the audio frequency range plus 1 to 20
hz. basically a big coil would work.

i've thought about using a steel drum, but i don't have room for that in my
new QTH. mu metal rods would be very expensive, even ferrite would be
expensive for an 100,000 turn antenna.

not sure what to use. maybe steel core.

High permeability ferrite (manganese zinc) is fairly cheap in bead
form, and these can be glued or clamped together (with nylon
all-thread) to make arbitrarily long rod forms. For example, 5000u,
5/8th inch diameter, by 1 and 1/8th inch long beads (Steward part #
LFB159079-000) cost less than a dollar each from Digikey, in quantity
of 10. This will make an 11 inch long rod with very low loss at low
frequencys (less than 100 kHz). And the hole down the center eases
the problem of mounting the rod in a drill press to make the winding.
You just slip a chunk of 1/4" all-thread through the glued rod and
run a nut against each end.

gravity wrote:
i've been considering an antenna for the audio frequency range plus 1 to 20
hz. basically a big coil would work.

i've thought about using a steel drum, but i don't have room for that in my
new QTH. mu metal rods would be very expensive, even ferrite would be
expensive for an 100,000 turn antenna.

not sure what to use. maybe steel core.

Gravity



"Detecting Natural Electromagnetic Waves," The Amateur Scientist, Shawn
Carlson, Scientific American, May, 1996. 50,000 turns #30 wire on 1/2
inch rebar, 2 feet long. You'll have to make your own amplifier and low
pass filter.
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:

"Detecting Natural Electromagnetic Waves," The Amateur Scientist, Shawn
Carlson, Scientific American, May, 1996. 50,000 turns #30 wire on 1/2
inch rebar, 2 feet long. You'll have to make your own amplifier and low
pass filter.

Rebar has a horrible B-H curve, and low permeability. You would do
better with a length of black iron pipe that you annealed after you
sawed a slit in it, lengthwise, to reduce eddy current losses.

John Popelish wrote:
Tom Donaly wrote:

"Detecting Natural Electromagnetic Waves," The Amateur Scientist,
Shawn Carlson, Scientific American, May, 1996. 50,000 turns #30 wire
on 1/2 inch rebar, 2 feet long. You'll have to make your own amplifier
and low
pass filter.


Rebar has a horrible B-H curve, and low permeability. You would do
better with a length of black iron pipe that you annealed after you
sawed a slit in it, lengthwise, to reduce eddy current losses.

It's what Shawn Carlson used. He also used mu metal which he got from
Scientific Alloys in R.I. Much better, but pricey.
73,
Tom Donaly, KA6RUH

"Tom Donaly" wrote in message
.com...
John Popelish wrote:
Tom Donaly wrote:

"Detecting Natural Electromagnetic Waves," The Amateur Scientist,
Shawn Carlson, Scientific American, May, 1996. 50,000 turns #30 wire
on 1/2 inch rebar, 2 feet long. You'll have to make your own amplifier
and low
pass filter.


Rebar has a horrible B-H curve, and low permeability. You would do
better with a length of black iron pipe that you annealed after you
sawed a slit in it, lengthwise, to reduce eddy current losses.

It's what Shawn Carlson used. He also used mu metal which he got from
Scientific Alloys in R.I. Much better, but pricey.

it's my understanding that you can use steel because the frequencies are
very low. however, i plan to research this further.

one thing i'm not clear on is coil diameter and air core. every dollar
spent on a metal core could be utilized for more turns for the antenna. and
i'm not sure if a big coil would have better aperture and gain than a small
diameter.

one thing i'm noticing is that there are basically two types of antennas.
one type is built by amateurs and is basically guesswork or based on prior
designs. the other type is built by professionals, often doing research in
earthquakes.

Gravity

73,
Tom Donaly, KA6RUH

gravity wrote:

one thing i'm not clear on is coil diameter and air core. every dollar
spent on a metal core could be utilized for more turns for the antenna. and
i'm not sure if a big coil would have better aperture and gain than a small
diameter.

one thing i'm noticing is that there are basically two types of antennas.
one type is built by amateurs and is basically guesswork or based on prior
designs. the other type is built by professionals, often doing research in
earthquakes.

A high permeability rod intercepts flux from a volume of space a
little less than a sphere with a diameter equal to the rod length. An
air core (short length to diameter ratio) coil intercepts flux from a
volume of space a bit larger than a sphere with a diameter equal to
the diameter of the coil. The air core coil has the advantage of
being relatively light and cheap. The iron core rod takes up a little
less space, and allows the coil to be electro statically shielded a
lot easier. It also produces the the same inductance with a much
shorter length of wire, so, for the same gauge wire, the coil
resistance is lower. With good winding technique, I think the stray
capacitance can also be lower. If the coil is wound on a tube, you
can also try different cores with little effort.

John Popelish wrote:
"The iron core rod takes up a little less space---."

A relay-coil works well for me.

Best regards, Richard Harrison, KB5WZI

gravity wrote:
i've been considering an antenna for the audio frequency range plus 1 to 20
hz. basically a big coil would work.

i've thought about using a steel drum, but i don't have room for that in my
new QTH. mu metal rods would be very expensive, even ferrite would be
expensive for an 100,000 turn antenna.

not sure what to use. maybe steel core.

Gravity



You can always use an active antenna.

Here's one the claims performance from
30 Hz to 50 MHz.

www.ets-lindgren.com/manuals/3301B.pdf

Chuck