wrote:
Roy,

I decided to go with a 20-meter 4 square. I wonder if any people have
experience with 4-squares that they can share with me. I have
considered some construction details give available materials, and I
have some questions.

I've built and used a few, for 40 meters.

1) Can I shorten each element by using an inverted L rather than
straight vertical, with a pipe as vertical part and a wire as
horizontal part? I have heard that matching is far less of a problem
this way also.

You can make a 4 square from any kind of element. EZNEC can tell you
what effect the element shape will have. I strongly recommend against
designing the antenna to get the best or easiest match. Design the
antenna for the best performance, then design whatever matching
arrangement you need in order to match it. An exception to this general
rule is that antennas with an exceptionally low resistance or high
reactance might not be practical because of the problem of matching
system loss, so such an antenna might need redesign in order to be
practical.

2) Where can I find or build a reasonably inexpensive phase box?

Chapter 8 of the ARRL Antenna Book describes how to design one. See also
"The Simplest Phased Array Feed System - That Works" and accompanying
program Simpfeed, available from http://eznec.com/Amateur/Articles/.

3) For the vertical part, I am wanting to a dig a hole 2 foot across by
3 foot down, and fill with concrete. Into this I would insert a 5
foot length of 1 1/2 inch steel support pipe about midway, so that 2
1/2 feet are above ground. Into this I would mount a 10 foot length
of 3/4 inch steel pipe with a 2 1/2 foot insulated overlap of PVC
pipe. The 3/4 inch steel pipe would be the bottom of the actual
driven element. Into this I would mount a 10 foot length of 1/2 inch
aluminum pipe with a 2 foot metallic contact overlap, and then I would
finish with rod for vertical or wire for inverted L.

Wow, for a 20 meter 4-square? For each element on 40, I drove a 1-1/4" 8
foot galvanized chain link fence line pole 4 feet into the ground. (Our
soil is clay.) I cut a piece of heavy wall PVC pipe lengthwise into
quarters for insulators, and clamped the element to the line pole with
muffler clamps with a couple of pieces of the split PVC pipe in between.
The elements are three pieces of telescoping 6061-T6 tubing, beginning
with, as I recall, 1-1/8" at the bottom. They've been up for around 20
years now and survived a couple of pretty strong wind storms.


Question: how would the 2 1/2 foot overlap of a non-grounded metal
support pipe interfere with radiation of the vertical element?

Any shunt impedance will reduce the null depth if the array is adjusted
for the correct base current ratio. This is because a different fraction
of the current will be diverted from each element because of their
differing base impedances. However, I've found that the 4 foot overlap I
have doesn't reduce it noticeably. But my overlapping pipes are parallel
and, if I understand your description, yours will be coaxial. That'll
result in a lot more shunt capacitance, and a correspondingly greater
effect on the null. The main lobe won't be affected much.

Roy Lewallen, W7EL