AM Loop Antenna Design
 

I made a 15 inch square (broadcast band) loop antenna using 2 crossed
pieces of wood and about 14 turns of number 18 copper wire. I added
spreaders in the center sections to increase the spacing between the
windings and reduce the distributed capacitance. Works well and has a
Q factor of 100 or more at 600 KHz. I get about 800mV from a local
50KW station.

But the wire is concentrated around the outside perimeter of the loop
and I'm wondering if there is an advantage in winding the loop so that
the wire occupies more of the interior space. This would require a
longer winding to maintain the same inductance and would further
reduce the distributed capacitance, but would also increase the total
resistance somewhat. Seems like a longer winding in the same space
would produce a larger voltage, but at the expense of some additional
resistance which may degenerate it somewhat.

What would be the optimum given a 15X15 inch square space?

-Bill

AM Loop Antenna Design
 

On Mon, 14 Jul 2008 23:05:06 -0700 (PDT), Bill B
wrote:

What would be the optimum given a 15X15 inch square space?

Hi Bill,

You are already there (or, rather, you are already so close that you
wouldn't be able to tell the difference which would be a circle of 15
inch diameter). Subtended area counts for most.

73's
Richard Clark, KB7QHC

AM Loop Antenna Design
 

"Richard Clark" wrote in message
...
On Mon, 14 Jul 2008 23:05:06 -0700 (PDT), Bill B
wrote:

What would be the optimum given a 15X15 inch square space?

Hi Bill,

You are already there (or, rather, you are already so close that you
wouldn't be able to tell the difference which would be a circle of 15
inch diameter). Subtended area counts for most.

73's
Richard Clark, KB7QHC

If yer local to a 50kw station, why do you need an antenna all?

Walt, W2DU

AM Loop Antenna Design
 

Walter Maxwell wrote:

...
If yer local to a 50kw station, why do you need an antenna all?

Walt, W2DU



Walter:

Just guessing here, of course ...

Maybe he wants to null out that 50kw stratosphere burner and hear
another station on a on a cheaper radio on a close channel. LOL!

Regards,
JS

AM Loop Antenna Design
 

On Jul 14, 11:05 pm, Bill B wrote:
I made a 15 inch square (broadcast band) loop antenna using 2 crossed
pieces of wood and about 14 turns of number 18 copper wire. I added
spreaders in the center sections to increase the spacing between the
windings and reduce the distributed capacitance. Works well and has a
Q factor of 100 or more at 600 KHz. I get about 800mV from a local
50KW station.

But the wire is concentrated around the outside perimeter of the loop
and I'm wondering if there is an advantage in winding the loop so that
the wire occupies more of the interior space. This would require a
longer winding to maintain the same inductance and would further
reduce the distributed capacitance, but would also increase the total
resistance somewhat. Seems like a longer winding in the same space
would produce a larger voltage, but at the expense of some additional
resistance which may degenerate it somewhat.

What would be the optimum given a 15X15 inch square space?

-Bill

Optimum is wire around the outside. You want to capture as much of
the field as you reasonably can. Imagine it this way: if you have a
15x15 loop and put say a 5x5 loop inside it, co-axial with it, and put
the two in series, you get the sum of the two. But what is the
performance of a 5x5 loop relative to that of a 15x15 loop (given that
both are much smaller than a wavelength)? There's still some question
about the optimum arrangement of the wire around the outside, though.
The largest area (the largest total field flux) enclosed by a fixed
length perimeter would be where the perimeter is a circle, so there's
some advantage of making the loop more circular. It's not terribly
likely you'll notice much difference from your square, though. But
you might find it useful to download one of Reg Edwards' legacies,
RJELOOP3.EXE, "Multi-turn, square, frame (or loop), receiving
aerials." It will let you play with different wire sizes, numbers of
turns and wire spacings, and give you a good approximation of the
expected Q, equivalent shunt capacitance and efficiency.

Small loops at low frequencies can be useful at rejecting locally
generated noise from things like electric motors or even
microprocessors, because that near-field noise tends to be
predominantly electric field which is vertically polarized, but to do
that well, the loop must be symmetrical about a vertical axis.

Cheers,
Tom

AM Loop Antenna Design
 

On Jul 15, 6:03 am, "Walter Maxwell" wrote:
"Richard Clark" wrote in message

...

On Mon, 14 Jul 2008 23:05:06 -0700 (PDT), Bill B
wrote:

What would be the optimum given a 15X15 inch square space?

Hi Bill,

You are already there (or, rather, you are already so close that you
wouldn't be able to tell the difference which would be a circle of 15
inch diameter). Subtended area counts for most.

73's
Richard Clark, KB7QHC

If yer local to a 50kw station, why do you need an antenna all?

Walt, W2DU

I just use the local 50kw station as a reference. It's hard to see
microvolts from some far away station on a scope, so I just use the
big signals to make comparisons. I can see about 14 stations on a
scope connected directly to the loop, but the amplitudes vary from a
few millivolts to almost a volt.

-Bill

AM Loop Antenna Design
 

"Bill B" wrote in message
...
On Jul 15, 6:03 am, "Walter Maxwell" wrote:
"Richard Clark" wrote in message

...

On Mon, 14 Jul 2008 23:05:06 -0700 (PDT), Bill B
wrote:

What would be the optimum given a 15X15 inch square space?

Hi Bill,

You are already there (or, rather, you are already so close that you
wouldn't be able to tell the difference which would be a circle of 15
inch diameter). Subtended area counts for most.

73's
Richard Clark, KB7QHC

If yer local to a 50kw station, why do you need an antenna all?

Walt, W2DU

I just use the local 50kw station as a reference. It's hard to see
microvolts from some far away station on a scope, so I just use the
big signals to make comparisons. I can see about 14 stations on a
scope connected directly to the loop, but the amplitudes vary from a
few millivolts to almost a volt.

-Bill

hook a couple of them up to a rectifier and use them to charge batteries to
power your radio. might as well make some use of that rf that is passing
through you all the time!

AM Loop Antenna Design
 

On Jul 15, 4:35 pm, "Dave" wrote:
"Bill B" wrote in message

...



On Jul 15, 6:03 am, "Walter Maxwell" wrote:
"Richard Clark" wrote in message

. ..

On Mon, 14 Jul 2008 23:05:06 -0700 (PDT), Bill B
wrote:

What would be the optimum given a 15X15 inch square space?

Hi Bill,

You are already there (or, rather, you are already so close that you
wouldn't be able to tell the difference which would be a circle of 15
inch diameter). Subtended area counts for most.

73's
Richard Clark, KB7QHC

If yer local to a 50kw station, why do you need an antenna all?

Walt, W2DU

I just use the local 50kw station as a reference. It's hard to see
microvolts from some far away station on a scope, so I just use the
big signals to make comparisons. I can see about 14 stations on a
scope connected directly to the loop, but the amplitudes vary from a
few millivolts to almost a volt.

-Bill

hook a couple of them up to a rectifier and use them to charge batteries to
power your radio. might as well make some use of that rf that is passing
through you all the time!

Actually, I use a 20 watt solar panel to charge batteries that power a
car radio in my bedroom. At 12 cents a KWH, I figure I save 12 cents
in 50 hours under good conditions, but I don't leave the panel outside
all the time, just when the batteries get weak. It's good exercise
dragging the solar panel out from under my bed and putting it out in
the sunshine, and then putting it away again. It weighs about 17
pounds.

-Bill

AM Loop Antenna Design
 

Bill B wrote:
"What would be the optimum given a 15x15 inch square space?"

Terman`s 1955 opus on page 929 says:
"In particular, a loop antenna responds much less to the electric
induction field than does a simple wire antenna of comparable intercept
area. This is of importance because electric induction fields
predominate in the man-made noise that causes disturbances in padio
receivers, and this explains in part the popularity of loop antennas in
broadcast receivers.

Best regards, Richard Harrison, KB5WZI

AM Loop Antenna Design
 

Richard Harrison wrote:
Bill B wrote:
"What would be the optimum given a 15x15 inch square space?"

Terman`s 1955 opus on page 929 says:
"In particular, a loop antenna responds much less to the electric
induction field than does a simple wire antenna of comparable intercept
area. ...

Best regards, Richard Harrison, KB5WZI


Can't most of that be accounted for with the loops directional
properties? And, that is just another way of stating the importance of
the loops directional properties?

Regards,
JS