I have room to erect a "half square" (aka upside-down phased verticals?)
20-meter antenna to be fed at one corner (low-impedance location; attach
50-ohm coax) or at the bottom (high-impedance; use a matching network):

A B
+--------------+ 1/2wave long
| /| 1/4wave high
| / |
/ Matching Network
Coax

Unfortunately, I do NOT (because my house is in the way) have room
to make it a more-balanced curtain:

A B C
+--------------+--------------+
| /| |
| / | |
/
coax

However, if I skip the middle "vertical", I have room for four vertical
sections in a space that should have five:

A B C D E
+--------------+--------------+--------------+--------------+
| | this part will be about | |
| | 10 feet above the peak | |
of my house

FWIW, line ABCDE will be about 30 feet above ground.

I've never done any antenna modeling, and I've never had any "feel" for
antenna phasing (EE degree notwithstanding), but I suspect feeding it
at the original corner (B) will result in somewhat unbalanced currents
almost everywhere.

QUESTION: Is there any not-too-difficult way to feed it at point C,
especially without a lot of cut-and-try (since a lot of
tree- and ladder-climbing will be involved)?

What about, for example, bringing x-wavelengths of coax BC and CD to a
common point somewhere above ground level (my shack is in the basement)
and connect them with a T to the coax that goes through the wall to
the rig? What lengths?
--
--Myron A. Calhoun.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448
NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol)

Its pretty hard to make recommendations without knowing, besides your
driven element conductor and proposed feedline, what other conducting
elements are nearby (housewiring, power lines, metal fences, metal
plumbing, etc.). The simplest and fastest approach would be to hook up
whatever you have, match it with an antenna tuner to your rig, and get on
the air and see if you can make contacts and ask what your signal report
is. Usually, if you can hear stations and the S meter is somewhere in the
middle of the scale, then they should hear you. You can tweak, adjust,
improve from that point on (and assess your TVI, BCI, and other
interference problems, too).

===== no change to below, included for reference and context =====

On Sun, 2 Oct 2005, wrote:

I have room to erect a "half square" (aka upside-down phased verticals?)
20-meter antenna to be fed at one corner (low-impedance location; attach
50-ohm coax) or at the bottom (high-impedance; use a matching network):

A B
+--------------+ 1/2wave long
| /| 1/4wave high
| / |
/ Matching Network
Coax

Unfortunately, I do NOT (because my house is in the way) have room
to make it a more-balanced curtain:

A B C
+--------------+--------------+
| /| |
| / | |
/
coax

However, if I skip the middle "vertical", I have room for four vertical
sections in a space that should have five:

A B C D E
+--------------+--------------+--------------+--------------+
| | this part will be about | |
| | 10 feet above the peak | |
of my house

FWIW, line ABCDE will be about 30 feet above ground.

I've never done any antenna modeling, and I've never had any "feel" for
antenna phasing (EE degree notwithstanding), but I suspect feeding it
at the original corner (B) will result in somewhat unbalanced currents
almost everywhere.

QUESTION: Is there any not-too-difficult way to feed it at point C,
especially without a lot of cut-and-try (since a lot of
tree- and ladder-climbing will be involved)?

What about, for example, bringing x-wavelengths of coax BC and CD to a
common point somewhere above ground level (my shack is in the basement)
and connect them with a T to the coax that goes through the wall to
the rig? What lengths?
--
--Myron A. Calhoun.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448
NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol)