On Nov 30, 5:55*pm, wrote:
Richard Clark wrote:
On Sun, 30 Nov 2008 21:45:03 GMT, wrote:

Art Unwin wrote:
Since we are at the low sun cycle I shoose
1" hexigon poultry wire for the mash on my 3 metre dish
At what frequency will there be a noticable effect on aperture
starting with top band?
Many thanks
Art KB9MZ...,XG

The rule of thumb is things less that .1 wavelengths in size have
negligable effects, so roughly up to about 1 GHz.

Hi Jim,

You neglect to mention that a 3 meter dish would be wholly (no pun
intended) transparent to RF in the top band. *It could be solid metal
to no notice by a radiator (or receiver).

It would be like blocking the sound 3 feet from the stage at a Led
Zepplin concert with a Japanese parasol. * -Huh?-

73's
Richard Clark, KB7QHC

Yeah, I foolishly forgot the source of the question and assumed "top
band" meant highest useable frequency.

Unless I hosed the math, a 3 m dish would be a little over 10 db
isotropic at 2 m, so the combinatation would "work" from 2 m to 23 cm.

--
Jim Pennino

Remove .spam.sux to reply.

I ask the question because the radiator is a helix end fed, helix
being approx 0.3 M diameter. Intuitively, I thought that the 3 M dish
would be large enough
and thus needed a check on the perforations. Could you show how the
"combination" changed things so drastically so I may benefit from the
question?
I stated "intuitively" since the radiation is axia with respect to the
helix
Many thanks
Art

Art Unwin wrote:
On Nov 30, 5:55Â*pm, wrote:
Richard Clark wrote:
On Sun, 30 Nov 2008 21:45:03 GMT, wrote:

Art Unwin wrote:
Since we are at the low sun cycle I shoose
1" hexigon poultry wire for the mash on my 3 metre dish
At what frequency will there be a noticable effect on aperture
starting with top band?
Many thanks
Art KB9MZ...,XG

The rule of thumb is things less that .1 wavelengths in size have
negligable effects, so roughly up to about 1 GHz.

Hi Jim,

You neglect to mention that a 3 meter dish would be wholly (no pun
intended) transparent to RF in the top band. Â*It could be solid metal
to no notice by a radiator (or receiver).

It would be like blocking the sound 3 feet from the stage at a Led
Zepplin concert with a Japanese parasol. Â* -Huh?-

73's
Richard Clark, KB7QHC

Yeah, I foolishly forgot the source of the question and assumed "top
band" meant highest useable frequency.

Unless I hosed the math, a 3 m dish would be a little over 10 db
isotropic at 2 m, so the combinatation would "work" from 2 m to 23 cm.

--
Jim Pennino

Remove .spam.sux to reply.

I ask the question because the radiator is a helix end fed, helix
being approx 0.3 M diameter. Intuitively, I thought that the 3 M dish
would be large enough
and thus needed a check on the perforations. Could you show how the
"combination" changed things so drastically so I may benefit from the
question?
I stated "intuitively" since the radiation is axia with respect to the
helix
Many thanks
Art

A helix doesn't radiate in the axial mode unless the circumference is
between about 0.75 and 1.33 wavelengths.

The would put the minimum frequency for a .3 m diameter helix at about
240 Mhz and the maximum frequency at about 420 Mhz.

Also, the reflector for a helix is a flat surface, not a dish, and is
normally between about 0.8 to 1.1 wavelengths in diameter. If you make
it larger, the sidelobe levels increase.


--
Jim Pennino

Remove .spam.sux to reply.

On Nov 30, 7:05*pm, wrote:
Art Unwin wrote:
On Nov 30, 5:55*pm, wrote:
Richard Clark wrote:
On Sun, 30 Nov 2008 21:45:03 GMT, wrote:

Art Unwin wrote:
Since we are at the low sun cycle I shoose
1" hexigon poultry wire for the mash on my 3 metre dish
At what frequency will there be a noticable effect on aperture
starting with top band?
Many thanks
Art KB9MZ...,XG

The rule of thumb is things less that .1 wavelengths in size have
negligable effects, so roughly up to about 1 GHz.

Hi Jim,

You neglect to mention that a 3 meter dish would be wholly (no pun
intended) transparent to RF in the top band. *It could be solid metal
to no notice by a radiator (or receiver).

It would be like blocking the sound 3 feet from the stage at a Led
Zepplin concert with a Japanese parasol. * -Huh?-

73's
Richard Clark, KB7QHC

Yeah, I foolishly forgot the source of the question and assumed "top
band" meant highest useable frequency.

Unless I hosed the math, a 3 m dish would be a little over 10 db
isotropic at 2 m, so the combinatation would "work" from 2 m to 23 cm.

--
Jim Pennino

Remove .spam.sux to reply.

I ask the question because the radiator is a helix end fed, helix
being approx 0.3 M diameter. Intuitively, I thought that the 3 M dish
would be large enough
and thus needed a check on the perforations. Could you show how the
"combination" changed things so drastically so I may benefit from the
question?
I stated "intuitively" since the radiation is axia with respect to the
helix
Many thanks
Art

A helix doesn't radiate in the axial mode unless the circumference is
between about 0.75 and 1.33 wavelengths.

The would put the minimum frequency for a .3 m diameter helix at about
240 Mhz and the maximum frequency at about 420 Mhz.

Also, the reflector for a helix is a flat surface, not a dish, and is
normally between about 0.8 to 1.1 wavelengths in diameter. If you make
it larger, the sidelobe levels increase.

--
Jim Pennino

Remove .spam.sux to reply.

No, No, No. That is not correct. Just as Kraus over estimated the gain
of helix antennas he also made a mistake
in specifying a particular helix angle as well as the impression that
one needs a large diameter helix with reference to wave length.
Ofcourse his work is over 50 years old and is being wittled down with
futher investigation.
I modeled it against perfect ground as the latest papers state that a
wall around the bottom where there is maximum current provides best
gain.
Thus I see the deep and large diameter dish as being an equivalent.
If .1 WL is a rule of thumb then it would seem your first response is
correct.
That is my personal view but I am open to contradiction hopefully with
reasons why
Art

Art Unwin wrote:
On Nov 30, 7:05Â*pm, wrote:
Art Unwin wrote:
On Nov 30, 5:55Â*pm, wrote:
Richard Clark wrote:
On Sun, 30 Nov 2008 21:45:03 GMT, wrote:

Art Unwin wrote:
Since we are at the low sun cycle I shoose
1" hexigon poultry wire for the mash on my 3 metre dish
At what frequency will there be a noticable effect on aperture
starting with top band?
Many thanks
Art KB9MZ...,XG

The rule of thumb is things less that .1 wavelengths in size have
negligable effects, so roughly up to about 1 GHz.

Hi Jim,

You neglect to mention that a 3 meter dish would be wholly (no pun
intended) transparent to RF in the top band. Â*It could be solid metal
to no notice by a radiator (or receiver).

It would be like blocking the sound 3 feet from the stage at a Led
Zepplin concert with a Japanese parasol. Â* -Huh?-

73's
Richard Clark, KB7QHC

Yeah, I foolishly forgot the source of the question and assumed "top
band" meant highest useable frequency.

Unless I hosed the math, a 3 m dish would be a little over 10 db
isotropic at 2 m, so the combinatation would "work" from 2 m to 23 cm.

--
Jim Pennino

Remove .spam.sux to reply.

I ask the question because the radiator is a helix end fed, helix
being approx 0.3 M diameter. Intuitively, I thought that the 3 M dish
would be large enough
and thus needed a check on the perforations. Could you show how the
"combination" changed things so drastically so I may benefit from the
question?
I stated "intuitively" since the radiation is axia with respect to the
helix
Many thanks
Art

A helix doesn't radiate in the axial mode unless the circumference is
between about 0.75 and 1.33 wavelengths.

The would put the minimum frequency for a .3 m diameter helix at about
240 Mhz and the maximum frequency at about 420 Mhz.

Also, the reflector for a helix is a flat surface, not a dish, and is
normally between about 0.8 to 1.1 wavelengths in diameter. If you make
it larger, the sidelobe levels increase.

--
Jim Pennino

Remove .spam.sux to reply.

No, No, No. That is not correct.

Yes, yes, yes, it is all corrct.

Just as Kraus over estimated the gain
of helix antennas he also made a mistake

Nothing was said about gain.

in specifying a particular helix angle

Nothing was said about the helix angle.

as well as the impression that
one needs a large diameter helix with reference to wave length.

A circumferance of 0.75 to 1.33 wavelengths is required for radiation
in the axial mode.

Ofcourse his work is over 50 years old and is being wittled down with
futher investigation.

Nope; correctness has no expiration date.

I modeled it against perfect ground

A pointless exercise.

as the latest papers state that a
wall around the bottom where there is maximum current provides best
gain.

What papers are these; the ones from the outhouse?

A short "wall" around the outer edge of the reflector reduces side lobes.

Thus I see the deep and large diameter dish as being an equivalent.

Most people would call that delusional.

If .1 WL is a rule of thumb then it would seem your first response is
correct.

Of course my first response was correct; things smaller than 0.1 wavelengths
can usually be ignored.


--
Jim Pennino

Remove .spam.sux to reply.

On Nov 30, 7:55*pm, wrote:
Art Unwin wrote:
On Nov 30, 7:05*pm, wrote:
Art Unwin wrote:
On Nov 30, 5:55*pm, wrote:
Richard Clark wrote:
On Sun, 30 Nov 2008 21:45:03 GMT, wrote:

Art Unwin wrote:
Since we are at the low sun cycle I shoose
1" hexigon poultry wire for the mash on my 3 metre dish
At what frequency will there be a noticable effect on aperture
starting with top band?
Many thanks
Art KB9MZ...,XG

The rule of thumb is things less that .1 wavelengths in size have
negligable effects, so roughly up to about 1 GHz.

Hi Jim,

You neglect to mention that a 3 meter dish would be wholly (no pun
intended) transparent to RF in the top band. *It could be solid metal
to no notice by a radiator (or receiver).

It would be like blocking the sound 3 feet from the stage at a Led
Zepplin concert with a Japanese parasol. * -Huh?-

73's
Richard Clark, KB7QHC

Yeah, I foolishly forgot the source of the question and assumed "top
band" meant highest useable frequency.

Unless I hosed the math, a 3 m dish would be a little over 10 db
isotropic at 2 m, so the combinatation would "work" from 2 m to 23 cm.

--
Jim Pennino

Remove .spam.sux to reply.

I ask the question because the radiator is a helix end fed, helix
being approx 0.3 M diameter. Intuitively, I thought that the 3 M dish
would be large enough
and thus needed a check on the perforations. Could you show how the
"combination" changed things so drastically so I may benefit from the
question?
I stated "intuitively" since the radiation is axia with respect to the
helix
Many thanks
Art

A helix doesn't radiate in the axial mode unless the circumference is
between about 0.75 and 1.33 wavelengths.

The would put the minimum frequency for a .3 m diameter helix at about
240 Mhz and the maximum frequency at about 420 Mhz.

Also, the reflector for a helix is a flat surface, not a dish, and is
normally between about 0.8 to 1.1 wavelengths in diameter. If you make
it larger, the sidelobe levels increase.

--
Jim Pennino

Remove .spam.sux to reply.

No, No, No. That is not correct.

Yes, yes, yes, it is all corrct.

Just as Kraus over estimated the gain
of helix antennas he also made a mistake

Nothing was said about gain.

in specifying a particular helix angle

Nothing was said about the helix angle.

as well as the impression that
one needs a large diameter helix with reference to wave length.

A circumferance of 0.75 to 1.33 wavelengths is required for radiation
in the axial mode.

Ofcourse his work is over 50 years old and is being wittled down with
futher investigation.

Nope; correctness has no expiration date.

I modeled it against perfect ground

A pointless exercise.

as the latest papers state that a
wall around the bottom where there is maximum current provides best
gain.

What papers are these; the ones from the outhouse?

A short "wall" around the outer edge of the reflector reduces side lobes.

Thus I see the deep and large diameter dish as being an equivalent.

Most people would call that delusional.

I am aware of that. One person once said the world was round!


If one was persuasive enough at the beginninghundred years or so later
if one said
the world was flat he would be called delusional.
If one was very persuasive in the first place he would be rediculed as
it was so obvious to all in the first place.
I hope you get to live another hundred years so that you can meld into
the new crowd of lemmings
Regards
Art





If .1 WL is a rule of thumb then it would seem your first response is
correct.

Of course my first response was correct; things smaller than 0.1 wavelengths
can usually be ignored.

--
Jim Pennino

Remove .spam.sux to reply.

Art Unwin wrote:

I am aware of that. One person once said the world was round!


Actually most learned people knew the world was round since before
Christ. The circumference was measured to something better than 10%
accuracy using only sticks and shadows.


If one was persuasive enough at the beginninghundred years or so later
if one said
the world was flat he would be called delusional.
If one was very persuasive in the first place he would be rediculed as
it was so obvious to all in the first place.
I hope you get to live another hundred years so that you can meld into
the new crowd of lemmings
Regards
Art

And delusional you are. No doubt about it.

tom
K0TAR

Tom Ring wrote:

...
Actually most learned people knew the world was round since before
Christ. The circumference was measured to something better than 10%
accuracy using only sticks and shadows.

tom
K0TAR

Actually, "sticks and shadows" is nice, for emphasis ... "wells and
shadows" would be a bit more accurate:

http://www.madsci.org/posts/archives...4968.Sh.r.html

Regards,
JS

Art wrote:
"I stated "intuitively" since the radiation is axia with respect to the
helix."

A 3 M diameter has about 9.42 M circumference so becomes an effective
axial radiator instead of a radial radiator at the frequency near where
its circumference becomes one wavelength. This frequency is
300/(pi)(diameter) or about 10 MHz. A reflecting surface to make an
axial helix unidirectional needs to be at least as large as the
projection of the helix on the surface of the reflector. Its diameter
should then be about 3 M or more and would be effective only at
frequencies exceeding 10 MHz which is where the helix becomes an
end-fire device anyway.

Best regards, Richard Harrison, KB5WZI

On Dec 1, 1:42*am, (Richard Harrison) wrote:
Art wrote:

"I stated "intuitively" since the radiation is axia with respect to the
helix."

A 3 M diameter has about 9.42 M circumference so becomes an effective
axial radiator instead of a radial radiator at the frequency near where
its circumference becomes one wavelength. This frequency is
300/(pi)(diameter) or about 10 MHz. A reflecting surface to make an
axial helix unidirectional needs to be at least as large as the
projection of the helix on the surface of the reflector. Its diameter
should then be about 3 M or more and would be effective only at
frequencies exceeding 10 MHz which is where the helix becomes an
end-fire device anyway.

Best regards, Richard Harrison, KB5WZI


Richard
That is good information that has a trend to my way of thinking.

A heads up as to where this information comes from would be very
helpfull to
me in my on going experiments

These ratios of diameter to length does have a penalty in wavelengths
used
but hopefully in less reflector diameter which is not to be viewed as
a phase enabling point of view
If one viewed a helix as an array of loop radiators then phasing would
be important but then prevents
the formation of smaller volume radiation designs. For those who rely
solely on "off the cuff" thoughts
may well deride what I am doing but I have done my homework and am now
pursueing implematation
since experiments consist of more than the exercises of the brain
without the need of personal observations,
without which advances would be crippled and science laboratories
would become extinct
My thinking now leans toward solenoid style with a air bound core for
maximum flux density
within the core in "rifle shot" pattern. I have had a similar antenna
for the 80 metre band where the helix diameter
is just 4" which is quite directional even tho as low as 30 feet!.
Thus I am very much encouraged in
this new design which is light enough for me to carry and install
together with improvements added over my past effort
tho it will not have the tilting feature at least not in the near
future. I am anxious to add the tilting feature some time next year
in an effort to extend individual QSO time as propagation changes ,but
it is low on program requirements
Best regards
Art Unwin KB9MZ..........xg

On Mon, 1 Dec 2008 08:27:22 -0800 (PST), Art Unwin
wrote:

I have had a similar antenna
for the 80 metre band where the helix diameter
is just 4" which is quite directional even tho as low as 30 feet!.

My transistor radio antenna of 50 years ago was smaller than that and
could do better at lower frequencies: Triple the wavelength, 4 times
smaller, and at one tenth the height. That is a 120 fold advantage
over your design. It cost $12, and the antenna came with it for free!

73's
Richard Clark, KB7QHC