"Richard Clark" wrote
In the future I will try to dumb down the technical and elevate
the popular.
____________

You can't dumb down your technical content much more than you already have.
It's essentially zero now. And don't bother us with your "popular"
rhetoric. It's only popular with you, I'm afraid.

RF

Richard Fry wrote:

"Richard Clark" wrote

In the future I will try to dumb down the technical and elevate
the popular.

____________

You can't dumb down your technical content much more than you already
have. It's essentially zero now. And don't bother us with your
"popular" rhetoric. It's only popular with you, I'm afraid.


So this is what antenna expert discourase is like?

- Mike KB3EIA -

Richard Fry wrote:
"Was the 0.05 lambda the pitch of the helix? If so, how many turns?"

I`ll quote Bill Orr for accuracy:
"Resonance can be established at a given frequency by the use of a
short, helically-wound element (Fig. 14). Treated bamboo poles (J L`s
choice), PVC plastic tubing, or fiberglass quad antenna spreaders can be
used as a form on which to wind the helix. Diameter for the helix must
be small in relation to length and a practical design makes use of a one
inch (25,4 mm) winding form. A helix length of about .05 wavelength or
more provides good results as a substitute for a full-size quarter
wavelength vertical antenna.

The amount of wire required for the winding depends upon helix length
and pitch (turns per inch). In general, a half-wavelength of no. 14
Formvar-coated wire is spirally wrapped on the form, with spacing
approximately equal to the wire diameter. This amount of wire
approximates a auarter-wave resonance"

There are helical antennas of two types. The "axial mode" invented by
John D. Kraus which radiates in the direction of the coil axis and the
"normal mode" helical antenna which radiates in directions perpendicular
to the coil axis, as does a short straight wire. Carried to extremes,
the pitch could go to zero,in which case the coil becomes a loop, or the
coil is stretched out to a straight wire. The helical antenna referred
to by Orr, is the normal-node helical antenna.

While the axial-mode helix is a broad-band antenna, the normal-mode
helix is a high-Q antenna and has restricted bandwidth. Orr has
something to say about the high-Q normal-mode helix:
"In order to prevent any high voltage discharge, a 12-ibch (30 cm)
diameter wire top hat is attached to the helix. Antenna resonance can be
adjusted by varying the size of the hat, or by adding a small extra
inductance at the base of the antenna."

There was also a question about directive gain which often brings a
surprised response. Terman is my source for directive gain. On page 871
of his 1955 edition of "Electronic and Radio Engineering" he gives the
directive gain, not in decibles, of 1.5 for the directive gain of the
elementary doublet. It is not isotropic. It is however infinitesimally
short. In the same Table 23-1, Terman gives the gain of the full
half-wave dipole as 1.64. There is precious little difference in
directivity or gain, which are two sides of the same coin, more or less.
Maybe Art can make a high-gain antenna of very short elements if he can
just get them to take a lot of current and not waste much to loss

Best regards, Richard Harrison, KB5WZI

On Wed, 30 Mar 2005 16:36:44 -0500, Michael Coslo
wrote:
So this is what antenna expert discourase is like?

Hi Mike,

No, that was abandoned long ago and an attempt to draw it back with a
novel topic of surface phonon polariton efficiency hits on antennas
was similarly abandoned as too easy (? who can tell what will lead to
a 600 entry thread?). However, the question:
"What does Do Wa Diddy mean?"
predictably blew a fuse.

73's
Richard Clark, KB7QHC

"Richard Harrison" wrote
Richard Fry wrote:
"Was the 0.05 lambda the pitch of the helix? If so, how many turns?"

I`ll quote Bill Orr for accuracy:
etc

Thanks. Maybe I'll model that in NEC and see what it shows. Or did you do
that already?

While the axial-mode helix is a broad-band antenna, the normal-mode
helix is a high-Q antenna and has restricted bandwidth.

The VSWR bandwidth of a normal-mode helix depends on its design. Below is a
link to one that, with branch feed, has a bandwidth of 12 MHz in the FM
broadcast band (see the text at the bottom of the first column of p 1).

http://www.dielectric.com/broadcast/brochures/DCR-M.pdf

Terman is my source for directive gain. On page 871
of his 1955 edition of "Electronic and Radio Engineering" he gives the
directive gain, not in decibles, of 1.5 for the directive gain of the
elementary doublet. It is not isotropic. It is however infinitesimally
short. In the same Table 23-1, Terman gives the gain of the full
half-wave dipole as 1.64.

The 1.5 and 1.64 are multipliers. Multiplying power by 1.64X is a gain of
2.15dBi, that is, 10*log(1.64).

RF

On Tue, 29 Mar 2005 15:09:25 -0500, Buck wrote:

How well would that work for shortening a J-Pole? would it be better
to use a shortened 1/2 wave dipole or would the J-Pole design be
better?

Hi Buck,

You may have noticed the vacuum of response - most have already seen
this movie and skipped out. However, for your benefit:

Like any small antenna, narrow bandwidth. Like any Hi-Z antenna, very
skitterish. Like any small antenna, lower gain.

For a helix standing roughly 4M tall for 40M band (which isn't
particularly short) under an 8 spoke top hat 6M wide, this exhibits a
drive point Z of 40000 Ohms. Put 100W into it and you will see 2KV at
the connector. That should take care of grass growing nearby.

EZNEC boldly announces there is loss, and the best gain is -2.6dBi.

The bandwidth spanned from 7.18MHz to 7.25MHz.

From there it is only a matter of adding the critical matching
section.

OR

Throw away the helix and use a straight support, shorten the 8 spoke
top hat to 4M wide and the drive point is an easier match at 13 Ohms.
No lethal voltages at the drive point, lower loss, more gain (albeit
of 0.65dBi), more bandwidth 7.14MHz to 7.4MHz.

Still reduces to it's hardly worth the effort to change from one to
the other, but all the signs point to a better implementation without
the air cooled wire wound resistor. If you want to keep a coil in the
picture, you can put it in the conventional place, shorten the top hat
spokes yet some more, and find no more gain, and less bandwidth.

OR

Buy an SGC which proudly proclaims it will match a wet string.

OR

Throw away all this folderol, and build a full size antenna (roughly
twice as tall as these gomers). No matching issue, bandwidth up the
kazoo (7-7.5 MHz), no appreciable change in gain though (in other
words, that imperceptible 1dB delta).

All modeling performed using "Real/MiniNEC Ground" (not usually my
choice, but then no one else has stepped up to the bar).

OR

Go watch a movie you haven't seen before, it may have a surprise in
it.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
"What does Do Wa Diddy mean?"

The answer I recall is:
"It ain`t no town and it ain`t no city. `Tain`t a gosh darn thing but Do
Wa Diddy!"

Best regards, Richard Harrison, KB5WZI

My gawd! Is this the same Richard Clark which I just reported to mental
health for a three day observation???
Quick, where is a phone--I will and cancel that! grin

Regards

--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw
aboot speel-checkin it fer me?


"Richard Clark" wrote in message
...
On Tue, 29 Mar 2005 15:09:25 -0500, Buck wrote:

How well would that work for shortening a J-Pole? would it be better
to use a shortened 1/2 wave dipole or would the J-Pole design be
better?

Hi Buck,

You may have noticed the vacuum of response - most have already seen
this movie and skipped out. However, for your benefit:

Like any small antenna, narrow bandwidth. Like any Hi-Z antenna, very
skitterish. Like any small antenna, lower gain.

For a helix standing roughly 4M tall for 40M band (which isn't
particularly short) under an 8 spoke top hat 6M wide, this exhibits a
drive point Z of 40000 Ohms. Put 100W into it and you will see 2KV at
the connector. That should take care of grass growing nearby.

EZNEC boldly announces there is loss, and the best gain is -2.6dBi.

The bandwidth spanned from 7.18MHz to 7.25MHz.

From there it is only a matter of adding the critical matching
section.

OR

Throw away the helix and use a straight support, shorten the 8 spoke
top hat to 4M wide and the drive point is an easier match at 13 Ohms.
No lethal voltages at the drive point, lower loss, more gain (albeit
of 0.65dBi), more bandwidth 7.14MHz to 7.4MHz.

Still reduces to it's hardly worth the effort to change from one to
the other, but all the signs point to a better implementation without
the air cooled wire wound resistor. If you want to keep a coil in the
picture, you can put it in the conventional place, shorten the top hat
spokes yet some more, and find no more gain, and less bandwidth.

OR

Buy an SGC which proudly proclaims it will match a wet string.

OR

Throw away all this folderol, and build a full size antenna (roughly
twice as tall as these gomers). No matching issue, bandwidth up the
kazoo (7-7.5 MHz), no appreciable change in gain though (in other
words, that imperceptible 1dB delta).

All modeling performed using "Real/MiniNEC Ground" (not usually my
choice, but then no one else has stepped up to the bar).

OR

Go watch a movie you haven't seen before, it may have a surprise in
it.

73's
Richard Clark, KB7QHC

....I will call and cancel that... even!

--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw
aboot speel-checkin it fer me?


"John Smith" wrote in message
...
My gawd! Is this the same Richard Clark which I just reported to mental
health for a three day observation???
Quick, where is a phone--I will and cancel that! grin

Regards

--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion,
haw
aboot speel-checkin it fer me?


"Richard Clark" wrote in message
...
On Tue, 29 Mar 2005 15:09:25 -0500, Buck wrote:

How well would that work for shortening a J-Pole? would it be better
to use a shortened 1/2 wave dipole or would the J-Pole design be
better?

Hi Buck,

You may have noticed the vacuum of response - most have already seen
this movie and skipped out. However, for your benefit:

Like any small antenna, narrow bandwidth. Like any Hi-Z antenna, very
skitterish. Like any small antenna, lower gain.

For a helix standing roughly 4M tall for 40M band (which isn't
particularly short) under an 8 spoke top hat 6M wide, this exhibits a
drive point Z of 40000 Ohms. Put 100W into it and you will see 2KV at
the connector. That should take care of grass growing nearby.

EZNEC boldly announces there is loss, and the best gain is -2.6dBi.

The bandwidth spanned from 7.18MHz to 7.25MHz.

From there it is only a matter of adding the critical matching
section.

OR

Throw away the helix and use a straight support, shorten the 8 spoke
top hat to 4M wide and the drive point is an easier match at 13 Ohms.
No lethal voltages at the drive point, lower loss, more gain (albeit
of 0.65dBi), more bandwidth 7.14MHz to 7.4MHz.

Still reduces to it's hardly worth the effort to change from one to
the other, but all the signs point to a better implementation without
the air cooled wire wound resistor. If you want to keep a coil in the
picture, you can put it in the conventional place, shorten the top hat
spokes yet some more, and find no more gain, and less bandwidth.

OR

Buy an SGC which proudly proclaims it will match a wet string.

OR

Throw away all this folderol, and build a full size antenna (roughly
twice as tall as these gomers). No matching issue, bandwidth up the
kazoo (7-7.5 MHz), no appreciable change in gain though (in other
words, that imperceptible 1dB delta).

All modeling performed using "Real/MiniNEC Ground" (not usually my
choice, but then no one else has stepped up to the bar).

OR

Go watch a movie you haven't seen before, it may have a surprise in
it.

73's
Richard Clark, KB7QHC

On Fri, 1 Apr 2005 00:07:03 -0600, (Richard
Harrison) wrote:

Richard Clark wrote:
"What does Do Wa Diddy mean?"

The answer I recall is:
"It ain`t no town and it ain`t no city. `Tain`t a gosh darn thing but Do
Wa Diddy!"

Hi Richard,

You are a Gem!

73's
Richard Clark, KB7QHC