Cecil Moore wrote:

Richard Clark wrote:

How thick was the original radiator? Stainless steel's fine for
larger diameters, the pits for small diameters.


Speaking of skin effect, consider a threaded rod on
edge with all those hills and valleys.

/\/\/\/\/\/\/\/\/\/\/\
|\ \ \ \ \ \ \ \ \ \ \ |
/\/\/\/\/\/\/\/\/\/\/\

Does skin effect force the RF to flow up and down
the hills and valleys thus increasing the VF of
the threaded rod?


In a related fashion, if you have a sort of reverse copperweld, that is
to say copper wire plated with steel, does the skin effect mean the RF
is confined to the steel?

Since skin effect has to stop somewhere - I mean insulated wire doesn't
have the RF try to run on the insulation, at what point does skin effect
stop, resistance of the outer part of the wire as a factor?

Does skin effect and insulation have any relationship with velocity factor?


Or have I opened my mouth and removed all doubt as the old saying about
stupidity goes? 8^)

- Mike KB3EIA -

Does skin effect force the RF to flow up and down
the hills and valleys thus increasing the VF of
the threaded rod?
--
73, Cecil http://www.qsl.net/w5dxp

------------------------------------------------

Yes it does.

Skin depth in metals at HF is only a very few thousandths of an inch,
and less. The current has nowhere else to go except up, over, and
down the humps of the screw threads.

But in practice, the RF resistance is not increased very much because
the diameter of a screw is usually very much greater than the diameter
of, say, an antenna wire, and so its resistance is already quite low
before it is threaded.
----
Reg.

A Steel over Copper conductor -

At very high frequencies current will flow only on the outer surface
of the steel according to the conductivity of steel.

As frequency decreases, current will flow in the copper only when skin
depth in the steel is greater than the thickness of the steel
covering.

As frequency decreases further current will begin to flow deeper in
the copper according to the conductivity of copper.

The resulting resistance of the composite structure is the resistance
of the steel layer in parallel with the resistance of the layer of
copper, taking the currents flowing in each layer into account.

But at HF, unless the steel layer is microscopically thin, the
resulting resistance will be practically the same as that of a solid
steel conductor.
----
Reg, G4FGQ

Reg Edwards wrote:
Skin depth in metals at HF is only a very few thousandths of an inch,
and less. The current has nowhere else to go except up, over, and
down the humps of the screw threads.

Imagine a rod with 60 degree notches cut out of it
such that the RF path is twice as long as is the rod.
VF = 0.5? 1/4WL vertical = 117/F? 75m vertical = 31ft?
--
73, Cecil http://www.qsl.net/w5dxp


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Imagine a rod with 60 degree notches cut out of it
such that the RF path is twice as long as is the rod.
VF = 0.5? 1/4WL vertical = 117/F? 75m vertical = 31ft?
--
73, Cecil
=================================

Yes Cecil, I am imagining. Now what ?
----
Reg

Reg Edwards wrote:

Imagine a rod with 60 degree notches cut out of it
such that the RF path is twice as long as is the rod.
VF = 0.5? 1/4WL vertical = 117/F? 75m vertical = 31ft?

Yes Cecil, I am imagining. Now what ?

Reg, a very efficient 31 ft. resonant 75m vertical
would be a good thing, right?
--
73, Cecil, W5DXP

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Imagine a rod with 60 degree notches cut out of it
such that the RF path is twice as long as is the rod.
VF = 0.5? 1/4WL vertical = 117/F? 75m vertical = 31ft?

Yes Cecil, I am imagining. Now what ?

Reg, a very efficient 31 ft. resonant 75m vertical
would be a good thing, right?
--
73, Cecil, W5DXP

==============================
Cec, now I can see what you're getting at.

Firstly, wrong - the difference between a very efficient antenna and
a very efficient antenna is absolutely negligible and not worth the
extra labor involved.

Secondly, the expected 4-fold increase in loading inductance to tune
the antenna to one half of the original resonant frequency, as a
result of cutting threads or slots in the fat antenna rod, does not
and cannot occur.

But you win first prize for ingenuity. ;o)
----
Reg, G4FGQ

"Reg Edwards" wrote in message
...

Imagine a rod with 60 degree notches cut out of it
such that the RF path is twice as long as is the rod.
VF = 0.5? 1/4WL vertical = 117/F? 75m vertical = 31ft?

Yes Cecil, I am imagining. Now what ?

Reg, a very efficient 31 ft. resonant 75m vertical
would be a good thing, right?
--
73, Cecil, W5DXP

==============================
Cec, now I can see what you're getting at.

Firstly, wrong - the difference between a very efficient antenna and
a very efficient antenna is absolutely negligible and not worth the
extra labor involved.

Secondly, the expected 4-fold increase in loading inductance to tune
the antenna to one half of the original resonant frequency, as a
result of cutting threads or slots in the fat antenna rod, does not
and cannot occur.

But you win first prize for ingenuity. ;o)
----
Reg, G4FGQ


At frequencies such that the groove spacing is a half wavelength one might
see resonance effects.
Imagine a stack of discones.
Probably just another worthless academic curiosity.
And it's THEORY!

73, H. NQ5H

I think it would be possible to alter the "beam width" of the omni-antenna
(mobile) and so make it "better."
If you take the time to learn EZNEC or MMANA you can view this for yourself
in the plot of the radiation pattern....

Regards,
John

"Ken Bessler" wrote in message
news:A8c7e.14295$up2.5543@okepread01...
Is it possible to make a mobile 10m antenna that is
physically shorter than a 1/4 wave whip yet will
preform better than a 1/4 wave whip?

--
73's es gd dx de Ken KGØWX
Grid EM17ip, Flying Pigs #1055,
Digital On Six #350,
List Owner, Yahoo! E-groups:
VX-2R & FT-857

"John Smith" wrote in message
...
I think it would be possible to alter the "beam width" of the omni-antenna
(mobile) and so make it "better."
If you take the time to learn EZNEC or MMANA you can view this for
yourself in the plot of the radiation pattern....

Regards,
John

Thanks John but that's not what I meant. For the record,
I'm trying to understand some manufacturer's claims that
the antenna they sell, while smaller than a 1/4 wave whip
on 10m, puts out a better signal.

Here are the rules:

1) The antenna is at least 25% shorter than a 1/4 w whip
2) The antenna is made with ordinary materials - no friggin gold.
3) The antenna is omni-directional & vertically polarised
4) The feedline is Flexi 4XL, aka CQ-102
5) The antenna is mounted dead center on the roof of a van.
6) The antenna's mount is non magnetic - I.E. There is a good
DC/RF ground at both the base of the antenna & the radio.

The way I see it is there is no way to make an antenna that
meets all those rules and STILL has more than 2.14dbi gain
due to resistave losses.

Am I right?

--
73's es gd dx de Ken KGØWX
Grid EM17ip, Flying Pigs #1055,
Digital On Six #350,
List Owner, Yahoo! E-groups:
VX-2R & FT-857