Wow! Did I do sump'n wrong?

Wow! Did I do sump'n wrong?




Fuggetaboutit!

SL,

For a Cage Antenna 'using' Metal (conductive) "Spacers" for VHF and
UHF just may work.

But... Everything I have seen for HF (MW/SW) has non-conductive
spacers.
- - - wood, plastic, tie-off-ropes, etc.

* * * Here is an alternative idea:
Three-Five small 24" Hula-Hoops with 8-12 holes drilled into them for
the copperclad wire. Would be a quick and easy trial (proto-type)
model.
- Three to Five Feet (3Ft-5Ft) Top and Bottom "Cones".
- - Three to Five Feet (3Ft-5Ft) "Space" between the Hula-Hoops.
- - - Eight to Twelve (8-12) Wires 12Ft-30Ft Long.
- - - - Vertically Mounted with a Bottom Feed Point.

Note: Flexiable 1/2", 3/4" or 1" Black PVC Tubing that is designed
for Garden Watering Systems. Could be used for smaller circular
"Spacer" Loops. Form them to size and use a Wood Plug and Stapes to
join the ends. Then Drill the holes for the wires.

TIP: Simple Practial Considerations
- - - The "Rule-of-Thumb" in dealing with Mechanical Realities )

* Divide the Diameter of the Loops by Two(2) to 'determine' the
maximum "Number" of Wires that will fit around the perimeter of the
Loop.

* Multiply the Diameter by Five(5) to determine the appropriate
"Space" between the Loops.

EXAMPLES:
6" Loop = Three(3) Wires and Two Foot Spacing between the Loops.
8" Loop = Four(4) Wires and Three Foot Spacing between the Loops.
12" Loop = Six(6) Wires and Five Foot Spacing between the Loops.
16" Loop = Eight(8) Wires and Seven Foot Spacing between the Loops.
18" Loop = Nine(9) Wires and Eight Foot Spacing between the Loops.
20" Loop = Ten(6) Wires and Nine Foot Spacing between the Loops.
24" Loop = Twelve(12) Wires and Ten Foot Spacing between the Loops.


iane ~ RHF
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GoTo= http://groups.yahoo.com/group/SWL-AM-FM-Antenna/
- - - This is my Antenna ~Golbewym~ [My Web Log].
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= = (SpamLover)
= = = wrote in message . com...
Thank you all again for the deluge of tips & links!
This is getting seriously fun!

Quick update on my trials with copperclad (maybe just copperflashed)
metal-inert-gas continuous welding steelwi

- This stuff solders like heaven! Steel disperses heat less than
copper, and capillarity is amazing. Hot solder joints catch deep
between twisted wires.

- Steel is quite springy and retains shape. My spool is small (~5"
dia.) but if I release the wire it falls into 15" loops.

- I made a 20' dia. loop with 3+ rounds of this wire, and soldered it
at 6 spots all round. Very light and elastic.

You know where I'm heading. I would like to try a lightweight soldered
all-steel cage, and rustproof it with one of those steel-blackening
nitric acid paints.

As a trial, I'd do a short cage with two 20" rings, maybe 2' between
them, and 3' end cones, paint it all, and hang it out in the elements,
weight-loaded.

The INEVITABLE QUESTION
=== Do cage spreaders HAVE to be insulating? ===

Uneducated guess: as VHF/UHF discones are made out of either radials
or sheet metal, I'd say that shorting spacers should be OK.

=== Do spreaders HAVE to be insulating? ===

YES for sure, for sure. The cage should be really folded dipole, one "wire"
going up (support, and grounded at the bottom) the other wire on the outside
(cage) coming down and fed against the ground or radials. Unless you just want
to make it fat radiator, then it doesn't matter.

Uh? AFAIK, a cage is not a folded monopole.

The "inside" vertical conductor would be shielded by the cage itself
('cept for its very bottom tip, which is grounded) and would not
radiate ('cept locally, within the cage, hence autocanceled). Apart
from discones I also remember seeing multi-kW 1940's TV dipole arrays
in which arms were huge, bulbous surfaces without slots.

This is getting *seriously* complicated.

One should be all thumbs to afford enough rules-of-thumb.

Some spreaders are indeed conductive.
But perhaps the fastening system acts as insulator.
http://www.stockroom.com/j030plus.htm
http://www.stockroom.com/j032plus.htm
You never know.

On 4 Nov 2003 11:47:55 -0800, (SpamLover) wrote:

Uh? AFAIK, a cage is not a folded monopole.

The "inside" vertical conductor would be shielded by the cage itself
('cept for its very bottom tip, which is grounded) and would not
radiate ('cept locally, within the cage, hence autocanceled). Apart
from discones I also remember seeing multi-kW 1940's TV dipole arrays
in which arms were huge, bulbous surfaces without slots.

Hi Filippo,

A cage can be a folded monopole (or folded dipole). Has nothing to do
with radiation as this is simply a transformer (not BalUN but
conventional transformer) and shielding the primary or secondary
(depending on which side is driven) does not interfere with either the
transformer action, nor radiation. The trick is to not short out the
skirt to the interior wire (if it exists - and it should to make
sense) at the driven end.

You can also construct a folded mono/dipole by segregating one wire
from the remaining bunch at the driven end (if there is no interior
wire). One of the virtues of a folded mono/dipole is the increase in
apparent radiator thickness causing a wider match range - a cage is
conceptually the same, but typically more extreme in its attempt to
create a thicker radiator.

The discone is another broad band radiator whose characteristics
follow this conceptual sense of building a thicker radiator. Consult:
http://www.qsl.net/kb7qhc/antenna/Discone/discone.htm
to observe how the flare of the skirt affects matching over frequency.

73's
Richard Clark, KB7QHC