5/8 over 5/8 over 5/8.. On 2m - Looking for ideas
 

Hi All

I will be moving to a house early next year that has 90ft trees
scattered around the backyard. Rather than setup a tower (initially
anyway) I am looking at hanging a wire (1/2" braid) 2 metre collinear
for a rope between the trees and feeding it from the bottom end.

Firstly talking about phasing sections. Has anyone come accross the
maths/size of using a single turn of stiff wire (looks like a ring
match) to go between the elements? Was thinking a short length of PVC
pipe with dowel or fibreglass spacers. How big?

What is the general figure of merit for shortening the topmost element
by when joined to a (say) PVC insulator.

And feeding. Was thinking about the J pole type match - The two parallel
wires 1/4 wavelenth long and a direct coax feed a few inches from the
bottom. Are there any better end/voltage fed methods?

Any thoughts or other construction methods/ideas appreciated.

Cheers Bob VK2YQA

On Thu, 18 Nov 2004 20:50:10 +1100, Bob Bob
wrote:
Any thoughts or other construction methods/ideas appreciated.

Hi Bob,

Given the title of the thread and the nature of your quest, I would
suggest you research the "Franklin Array."

73's
Richard Clark, KB7QHC

Richard Clark wrote:
"I would suggest you research the "Franklin Array"."

Current reverses at the open-circuit end of an antenna. 180-degrees back
from the open end it reverses again. Current flowing in opposite
directions begins to reduce the field strength perpendicular to the
antenna when the total length reaches 5/8-wavelength.

At a point 1/2-wave or 5/8-wave back from the open circuit, a phase
inverter is used to produce (2) mostly in-phase antenna segments. Some
ways to get in-phase segments are to drive the array at that point. Or,
to connect the segments through a short-circuit 1/4-wave stub. The
"Super-J Maritime Antenna" in the ARRL Antenna Book uses this method.
Or, use a lumped network in place of the short-circuit stub.

Kraus shows an interesting and simple phase inverter in Figure 23-21(b)
on page 824 of his 3rd edition of "Antennas". The inverters are
self-resonant coils. No external capacitors required. They are "traps".

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Kraus shows an interesting and simple phase inverter in Figure 23-21(b)
on page 824 of his 3rd edition of "Antennas". The inverters are
self-resonant coils.

Since there is no phase shift through a coil, how could that
possibly work? :-)
--
73, Cecil, W5DXP

Cecil, W5DXP wrote:
"Since there is no phase shift through a coil, how could that possibly
work?"

You put a sticker on the coil maming it a retardation coil. It then must
delay the energy and that is phase shift by definition.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
You put a sticker on the coil maming it ...

Watch out - the society for prevention of cruelty to
coils will get you.

"Bob Bob" wrote in message
...
Hi All

I will be moving to a house early next year that has 90ft trees scattered
around the backyard. Rather than setup a tower (initially anyway) I am
looking at hanging a wire (1/2" braid) 2 metre collinear for a rope
between the trees and feeding it from the bottom end.

Firstly talking about phasing sections. Has anyone come accross the
maths/size of using a single turn of stiff wire (looks like a ring match)
to go between the elements? Was thinking a short length of PVC pipe with
dowel or fibreglass spacers. How big?

What is the general figure of merit for shortening the topmost element by
when joined to a (say) PVC insulator.

And feeding. Was thinking about the J pole type match - The two parallel
wires 1/4 wavelenth long and a direct coax feed a few inches from the
bottom. Are there any better end/voltage fed methods?

Any thoughts or other construction methods/ideas appreciated.

Cheers Bob VK2YQA

Bob,

I don't know about the 5/8, but you are basically on the right track. I once
bought an Andrew 1900 MHz vertical that claimed 8 or 10 dbi gain, non
directional. It had multiple radiators stacked vertically inside a plastic
tube about 1/2 inch OD, couple of feet tall. No idea how it was phased
internally, but don't think it had any coils in there. I had it mounted via
an N connector on top of a metal box, but don't think it required a ground
plane.

Tam/WB2TT