On 25 Oct, 12:45, Cecil Moore wrote:
art wrote:
No Cecil you are following a fatal aproach by using
lumped loaded circuitry which is a no no when measuring current speed.

Nope, I'm arguing against that approach, Art. Some
"experts" seem to like lumped load concepts but not
I. Dr. Corum warns against using lumped load concepts
for large coils and I agree with him.
--
73, Cecil http://www.w5dxp.com

Good for him. It appears that constant use of lumped circuit analysis
is gaining more votes against true science of today especially in
amateur
radio. Soon it will be promoted to a Law disregarding that it is
only theory based. Something akin to a poll
Regards
Art.

Umm a velocity factor of .50 might be attainable with a variation on
leaky coax... Some of the cheap stuff is already as slow as .66...
Off the top of my pointy head braided wires wrapped on your form (same
as you are currently doing) then potted in an appropriate dielectric
material for filling the braid interstices should slow things down
some more... The question extant is what material for potting (or for
adding to your potting resin) will further slow progression of the
wave front along the braid...
We know that solid polyethylene dielectric on coax results in a lower
vf than the foamed materials.. So it appears that denser material
results in slower wave progression... Perhaps UHMW, or similar might
suffice...
Other thoughts come along, such as a flat ribbon with a deeply
embossed pattern then filled with dielectric might be slower than
braided wire... Or even a ribbon of screening material similarily
filled...
Dunno... Interesting problem...

denny / k8do

Denny wrote:
Dunno... Interesting problem...

Not really - a helix can slow down a wave by
a factor of 50 or more. Approximately a foot and
a half of 75m Texas Bugcatcher stock will be self-
resonant at 4 MHz. That's 90 degrees of antenna
stuffed into about a foot and a half of coil.
90 degrees at 4 MHz is 61.5 feet. The VF of that
coil is 1.5/61.5 = 0.024. Actually, pretty simple.
--
73, Cecil http://www.w5dxp.com

On 25 Oct, 14:47, Cecil Moore wrote:
Denny wrote:
Dunno... Interesting problem...

Not really - a helix can slow down a wave by
a factor of 50 or more. Approximately a foot and
a half of 75m Texas Bugcatcher stock will be self-
resonant at 4 MHz. That's 90 degrees of antenna
stuffed into about a foot and a half of coil.
90 degrees at 4 MHz is 61.5 feet. The VF of that
coil is 1.5/61.5 = 0.024. Actually, pretty simple.
--
73, Cecil http://www.w5dxp.com

Yes Cecil I see where you are coming from
but and it is a big but the turns must be
exposed to radiate and it is that that one
must not lose sight upon
Art

"art" wrote in message
ups.com...
On 25 Oct, 14:47, Cecil Moore wrote:
Denny wrote:
Dunno... Interesting problem...

Not really - a helix can slow down a wave by
a factor of 50 or more. Approximately a foot and
a half of 75m Texas Bugcatcher stock will be self-
resonant at 4 MHz. That's 90 degrees of antenna
stuffed into about a foot and a half of coil.
90 degrees at 4 MHz is 61.5 feet. The VF of that
coil is 1.5/61.5 = 0.024. Actually, pretty simple.
--
73, Cecil http://www.w5dxp.com

Yes Cecil I see where you are coming from
but and it is a big but the turns must be
exposed to radiate and it is that that one
must not lose sight upon
Art

try a ctha that may do what you want.

art wrote:
Yes Cecil I see where you are coming from
but and it is a big but the turns must be
exposed to radiate and it is that that one
must not lose sight upon

I can only wish that my 75m Bugcatcher coil
had all of its losses going into radiation. :-)
--
73, Cecil http://www.w5dxp.com

"Cecil Moore"
Approximately a foot and a half of 75m Texas Bugcatcher
stock will be self-resonant at 4 MHz. That's 90 degrees of
antenna stuffed into about a foot and a half of coil.
__________

But that self-resonant coil is not the electrical equivalent of a 90-degree
linear antenna. A coil by itself is not a very efficient producer of EM
radiation, whether self-resonant or not.

RF

Richard Fry wrote:
"Cecil Moore"
Approximately a foot and a half of 75m Texas Bugcatcher
stock will be self-resonant at 4 MHz. That's 90 degrees of
antenna stuffed into about a foot and a half of coil.

But that self-resonant coil is not the electrical equivalent of a
90-degree linear antenna. A coil by itself is not a very efficient
producer of EM radiation, whether self-resonant or not.

I'm not saying anything about radiation efficiency
just commenting on the phase relationship between
the forward wave and reflected wave.

At the first self-resonant frequency, the feedpoint
impedance is purely resistive indicating that the coil
is indeed electrically 90 degrees long.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore"
At the first self-resonant frequency, the feedpoint
impedance is purely resistive indicating that the coil
is indeed electrically 90 degrees long.
___________

But that doesn't make the coil an "antenna," as you described it
for that condition.

RF

Richard Fry wrote:
"Cecil Moore"
At the first self-resonant frequency, the feedpoint
impedance is purely resistive indicating that the coil
is indeed electrically 90 degrees long.

But that doesn't make the coil an "antenna," as you described it
for that condition.

We know that helical antennas exist and radiate. The
form factor of a self-resonant 75m bugcatcher coil is
helical and will radiate (even though very inefficiently)
and contacts are more than likely possible. What is your
definition of "antenna"? A self-resonant 75m bugcatcher
coil is not all that different from an Isotron "antenna".
--
73, Cecil http://www.w5dxp.com