On Fri, 15 Oct 2010 09:24:15 -0400, Mike Coslo wrote:

Initial idea is to run the separate wires as taps on the coil. I'm
intending to run them on the outside of the coil, probably separated
about an inch away. The wires would then go to a (insert whizbang gadget
here that I'm still figuring out) which then switches taps as needed.
I'll probably start with manual switching.

Hi Mike,

A rare confab of actual antenna design details. No controversy. No
wonder there are so few postings. Mike, on this cat walk of
fashionable posing, you are a buzz-kill.

How long are those tap wires? In other words, is this manual switch
sitting on your dashboard?

There is also the matter of
that tuning coil at the bottom of the antenna to ground, which varies
between 8 turns of number 12 on a 1.5 inch diameter coil on 75/80
meters, to no coil at all on 20 meters, which is the highest frequency
it will tune at.

Why have a coil there at all?

The antenna itself is semi-standard bugcatcher, a four foot bottom
section, followed by the six inch coil, (standard GLA systems) followed
by another roughly foot and a half section, then a 16 inch Capacity hat,
then a spring and topped off with a 102 inch whip.

Uh-huh. So you have a "top" hat that is actually very close to the
center? A center hat as I might be wont to describe it?

I've often thought (and probably modeled at some point in the last 20
years) about putting such "top" hats at regular intervals along a
vertical radiator. Sort of like a bottle washing brush kind of
design.

Taps at the present
short out the remaining coil below themselves.

Back when we had more designers writing here, instead of Xerox junkies
and home-spun Platocrats, the discussion of shorted coils made them
apoplectic where those turns became huge losses. This is different
from the screwdriver approach which shields those turns.

Anyhow, I pretty much assumed that there might be some small tuning
differences on the lower frequencies,

Well, as I inferred, IFF you knew what frequency any unadorned
(unchanged) original design was going to reside at; then I could well
imagine it would shove that understanding under the bus. IFF, on the
other hand, you have no idea (other than a general one of plus or
minus one MHz) of where the initial state of tune was, then it
probably wouldn't matter.

but I was just making sure that I
wasn't running the road to perfidy with any hidden "gotchyas" - like if
a stinger goes too far into a loading coil - one of those things that
might not be completely intuitive until after the fact.

But of course you will (I'm looking forward to those stories) -
otherwise you would have bought an antenna with a guarantee. In
regard to this last I have to tailor a quote from one of my favorite
authors, Walter Mosely:
"...you won't get to enjoy the honey,
if you worry the bees be stingin' you."

73's
Richard Clark, KB7QHC

On 10/15/10 12:56 PM, Richard Clark wrote:

A rare confab of actual antenna design details. No controversy. No
wonder there are so few postings. Mike, on this cat walk of
fashionable posing, you are a buzz-kill.

8^)



How long are those tap wires? In other words, is this manual switch
sitting on your dashboard?

The initial plan is to have something perhaps located on the lower mast
so that I can experiment with it. the final version will be eletrically
or electronically switched, (most likely electrically) the switching
taking place at the antenna - probably located on the lower mast.


There is also the matter of
that tuning coil at the bottom of the antenna to ground, which varies
between 8 turns of number 12 on a 1.5 inch diameter coil on 75/80
meters, to no coil at all on 20 meters, which is the highest frequency
it will tune at.

Why have a coil there at all?

It's sort of the butternut HF6V (and family) thing, I can tune the
thing, but unless I place a Matching coil there, the minimum SWR might
be around 2.5 to one or even higher, except where the antenna is
becoming a more normal length. In the end, it's no doubt to compensate
for the crazy low impedance on a short antenna.


The antenna itself is semi-standard bugcatcher, a four foot bottom
section, followed by the six inch coil, (standard GLA systems) followed
by another roughly foot and a half section, then a 16 inch Capacity hat,
then a spring and topped off with a 102 inch whip.

Uh-huh. So you have a "top" hat that is actually very close to the
center? A center hat as I might be wont to describe it?

Yup. I had looked at placing it higher, but that ended up defeating my
tie down idea, and those cap hats are kinda like wind dams - In the end
I wanted it attached to some sturdy part of the antenna.

Taps at the present
short out the remaining coil below themselves.

Back when we had more designers writing here, instead of Xerox junkies
and home-spun Platocrats, the discussion of shorted coils made them
apoplectic where those turns became huge losses. This is different
from the screwdriver approach which shields those turns.

I'm wondering where the issue comes from. As I look at it, the shorting
is making the bottom part of the mast slightly longer. I have to imagine
that not shorting it would be worse. Dunno, though.



Anyhow, I pretty much assumed that there might be some small tuning
differences on the lower frequencies,

Well, as I inferred, IFF you knew what frequency any unadorned
(unchanged) original design was going to reside at; then I could well
imagine it would shove that understanding under the bus. IFF, on the
other hand, you have no idea (other than a general one of plus or
minus one MHz) of where the initial state of tune was, then it
probably wouldn't matter.

I'll end up knowing, my tap system so far is a modified clip that has a
marked place on the coil. It works ver well, when very well is defined
as stays on and sends to power where I want it.

What got me started was last weekend, out late at night in just about
the most rural area in Pennsylvania, dragging out a stepstool to change
80 meter taps. New moon, and I forgot my flashlight. While the antenna
"works" pretty well for the genre, needing a stepstool is just not that
wonderful.


but I was just making sure that I
wasn't running the road to perfidy with any hidden "gotchyas" - like if
a stinger goes too far into a loading coil - one of those things that
might not be completely intuitive until after the fact.

But of course you will (I'm looking forward to those stories) -
otherwise you would have bought an antenna with a guarantee.

I'll be updating as I go.


- 73 de Mike N3LI -

On Fri, 15 Oct 2010 14:35:53 -0400, Mike Coslo wrote:

Back when we had more designers writing here, instead of Xerox junkies
and home-spun Platocrats, the discussion of shorted coils made them
apoplectic where those turns became huge losses. This is different
from the screwdriver approach which shields those turns.

I'm wondering where the issue comes from. As I look at it, the shorting
is making the bottom part of the mast slightly longer. I have to imagine
that not shorting it would be worse. Dunno, though.

Hi Mike,

That, too, was part of the raging debate. I have long forgotten the
particulars, but I will hazard their argument. That is, in these
highly reactive designs there are large potentials and high currents.
With those circulating currents (the usual province of these
considerations are in the tuner) AND the proximity of a shorted turn,
you have a transformer relationship feeding the loss of the small
diameter wire and/or the resistive short (rarely do switches offer
optimal solutions in the face of truly enormous currents).

Screwdriver designs pre-empt this through the coil being nested inside
of the conductive cylinder - no transformer action, or at least so
goes the argument.

Reggie entered into these issues with his own observations about coil
length, diameter, winding pitch, and placement to summarize his
optimal design. You may want to look into that insofar as your base
loading goes.

73's
Richard Clark, KB7QHC