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Another thing that keeps floating up from the depths of my
subconscious...

How would a multi-turn loop having space between turns a significant
percentage of the loop diameter work relative to one that has closer
spacing? For instance, a 2-turn 36" diameter loop with 12" between
turns. My instincts tell me that there would be an increase in the
physical capture area of the loop due to its taking on a more 3-D
profile. This would lead to higher performance than a close-spaced
loop winding. How much increase in performance? Would there be an
optimal spacing? What about spacing equal to loop diameter?

Hmmm... obviously I need more copper... a LOT more! Uhh... got any
spare capacitors?

73,

'Bear' NH7SR

Contrary to my intuition, closely spaced windings seem to vastly
increase the Q of the antenna. I, too thought about the capture
volume, but then the capture volume of a spiral loop would be zero.
Aperature size appears to be everything in determining the
sensitivity of a loop. I made three identical 27 MHz loops, out of
10 guage, 20 guage, and 30 guage wire. All had the same
sensitivity, but the Q varied.

I have not researched the inter-winding capacitance question, but I
am beginning to suspect it doesn't have the effect I first assumed.
It seems to be much easier to encompass the whole band with a 9 to
250 pF tuning capacitor than a 9 to 365 or 9 to 500 pF capacitor.
Again - counter intuitive, but why did radio manufacturers make the
change? Wire is cheap compared to tuning capacitors. Especially
when the first 9 to 250 pF capacitors were probably special order.
I will get to the bottom of it when I have time. For now, loops
made of 24 guage hookup wire, turns wound flush, on large styrofoam
forms are light weight, easy to make, have fantastic Q's, and span
the whole band. I may get around to posting articles soon, plus
updating a lot of my old ones.

--- In loopantennas@..., "qrpbear" <qrpbear@y...> wrote:

Another thing that keeps floating up from the depths of my
subconscious...

How would a multi-turn loop having space between turns a

significant

percentage of the loop diameter work relative to one that has

closer

spacing? For instance, a 2-turn 36" diameter loop with 12" between
turns. My instincts tell me that there would be an increase in the
physical capture area of the loop due to its taking on a more 3-D
profile. This would lead to higher performance than a close-spaced
loop winding. How much increase in performance? Would there be an
optimal spacing? What about spacing equal to loop diameter?

Hmmm... obviously I need more copper... a LOT more! Uhh... got any
spare capacitors?

73,

'Bear' NH7SR

Bruce,

Curious... that goes contrary to my intuition also. It has always
been one of the "laws" of coil winding that best Q is obtained in
solenoid coils when the diameter to length ratio is square (1:1).

Ah... I just remembered best Q is with the diameter to length ratio
at 1:1 or greater! It still seems, though, that a solenoid type
multiturn loop with very wide spacing between turns should exhibit a
larger capture area due to its 3D form factor. Possibly it does but
it may be a case of diminishing returns once one has passed the one-
wire-diameter spacing rule.

I think I'll add that to my "build this someday" list. Mebbe a 3-turn
2' diameter with 1' between turns. I could always tell people it's a
new kind of Dreamcatcher... especially after I hang some feathers on
it.

My take on the capacitors is that they seem to be related to the eras
in which radios were built. Prior to the introduction of the All
American Five most radios used external antennas. The RF/Mixer stages
commonly used values as high as 500 pF. With the All American Five
the use of an oval spiral wound loop on the back of the radio became
common as did the 365 pF capacitor. With the introduction of ferrite
bars we began to see 220 pF capacitors being used for tuning. I think
the shift had more to do with the available inductance in a given
space than any other factor. Higher inductance requiring less
capacitance and exhibiting better Q (more signal voltage) resulting
in the ability to simplify design and reduce parts count.

73,

'Bear' NH7SR

--- In loopantennas@..., "Bruce Carter" <brucec@m...>
wrote:

Contrary to my intuition, closely spaced windings seem to vastly
increase the Q of the antenna. I, too thought about the capture
volume, but then the capture volume of a spiral loop would be

zero.

Aperature size appears to be everything in determining the
sensitivity of a loop. I made three identical 27 MHz loops, out of
10 guage, 20 guage, and 30 guage wire. All had the same
sensitivity, but the Q varied.

I have not researched the inter-winding capacitance question, but I
am beginning to suspect it doesn't have the effect I first

assumed.

It seems to be much easier to encompass the whole band with a 9 to
250 pF tuning capacitor than a 9 to 365 or 9 to 500 pF capacitor.
Again - counter intuitive, but why did radio manufacturers make the
change? Wire is cheap compared to tuning capacitors. Especially
when the first 9 to 250 pF capacitors were probably special order.
I will get to the bottom of it when I have time. For now, loops
made of 24 guage hookup wire, turns wound flush, on large styrofoam
forms are light weight, easy to make, have fantastic Q's, and span
the whole band. I may get around to posting articles soon, plus
updating a lot of my old ones.

--- In loopantennas@..., "qrpbear" <qrpbear@y...> wrote:

Another thing that keeps floating up from the depths of my
subconscious...

How would a multi-turn loop having space between turns a

significant

percentage of the loop diameter work relative to one that has

closer

spacing? For instance, a 2-turn 36" diameter loop with 12"

between

turns. My instincts tell me that there would be an increase in

the

physical capture area of the loop due to its taking on a more 3-D
profile. This would lead to higher performance than a close-

spaced

loop winding. How much increase in performance? Would there be an
optimal spacing? What about spacing equal to loop diameter?

Hmmm... obviously I need more copper... a LOT more! Uhh... got

any

spare capacitors?

73,

'Bear' NH7SR