I'm deciding to go with a 20 meter 4-square because it can hopefully
provide me with similar directivity and DX takeoff angle as a 20 meter
beam but without the hassle or height of a tower. A dipole only has
directivity in 2 directions, a 4 square can give me directivity in 4
directions with basic phasing and 8 directions high tech using ARRL
suggestions. The EZNEC plot was pretty awesome.

The Eternal Squire

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.

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.

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

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.

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

Thanks in advance,

The Eternal Squire

There's that "takeoff angle" again. Having a good "takeoff angle" is no
guarantee of good DX performance, and isn't a valid way to compare the
performance of two antennas.

You should model both the beam and the 4-square. Make sure you include a
realistic amount of ground loss resistance for whatever ground system
you think you can put down for the 4-square. Superimpose their elevation
patterns on the same plot, and see which really does best at low angles.
If you don't want to go to the trouble of modeling a beam, you can model
a simple dipole which has almost the same elevation pattern as a beam of
a few elements (in the forward direction) at the same height. Mentally
add the beam's gain relative to a dipole to the dipole's pattern. See if
the 4-square really is as good. It might change your mind.

Roy Lewallen, W7EL

wrote:
I'm deciding to go with a 20 meter 4-square because it can hopefully
provide me with similar directivity and DX takeoff angle as a 20 meter
beam but without the hassle or height of a tower. A dipole only has
directivity in 2 directions, a 4 square can give me directivity in 4
directions with basic phasing and 8 directions high tech using ARRL
suggestions. The EZNEC plot was pretty awesome.

The Eternal Squire

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

Dear Group:
Long, long experience with angles above the horizon that are used by DX
signals (at HF) indicates that the most useful angles are between 2 and 12
degrees. Comparing the expected gain of antennas at 6 degrees provides a
good figure-of-merit.

That said, if one has a low, horizontally polarized antenna with very
little gain at 6 degrees, you might still work DX using more than an optimum
number of hops (angle of more than ten degrees). However, you will work DX
fewer days per month than someone who gets significant gain at angles
smaller than ten degrees.

I emphasize what Roy has said: the so-called take-off-angle (equal to
the smallest angle at which peak gain occurs) of an antenna is not
necessarily an indicator of DX performance.

Another example is the case of a horizontally polarized antenna that is
over 3 WL high: it has a small TOA but is likely to have a null at an
important angle smaller than 12 degrees. In other words: the
too-high-antenna works very well some of the time, but a lower antenna works
better at other times.

A useful goal for the (single) optimum (for DX) antenna is an antenna that
has its second null (first null is at zero degrees) at an angle greater than
12 degrees and a first maximum (what is called by many the TOA) between 2
and 12 degrees.

The actual angle used at the transmitter end of a DX circuit is
sometimes quite different from that used at the receiver end.

73 Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Bill Turner" wrote in message
...
Roy Lewallen wrote:


An antenna doesn't have a single "radiation angle". It radiates at
all angles. The relevant question is how much does it radiate at the
particular angle of interest, not at which angle does it radiate the
most.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

That's true, except few if any hams have a specific "angle of
interest", since different angles are used at different times. For
most of us, the angle of maximum radiation gives a general indication
of how the antenna will perform. A better indication would be a
graphical representation. It's always a problem when one tries to
reduce a complex situation like this down to a single number.

73, Bill W6WRT

To Novices -

It is use of the term "take off angle" which causes all the confusion
surrounding DX and the "best" take off angles. It is a misnomer.

The elevation angle of a radio path between two stations is purely a
geometric function of their locations on the Earth's surface and the
heights of ionospheric reflecting layers. It has nothing whatever to
do with either of the antennas or ground conditions - except that it
is the best elevation angle at which an antenna beam should be
pointing.

If, purely by coincidence, the "take off angle" indicated by Eznec
happens to be the same as the exceedingly changeable "path elevation
angle" then all is well and good.

The true "take off angle" having maximum gain (another misnomer) for
any vertical antenna is always zero degrees, ie., it corresponds to
the always existent very strong groundwave. Whereas Eznec always
reports the groundwave strength as being zero. It is of no use in the
prediction of often-used ground waves between stations.

Whenever a resistive ground is involved, programs like Eznec do not
produce the true radiation pattern of an antenna. Not that there is
anything incorrect with Eznec. It is just the confusing description
of what it displays.
----
Reg.

Reg Edwards wrote:
. . . Whereas Eznec always
reports the groundwave strength as being zero. . .

If you're using the strict definition of "groundwave" as being the field
at an elevation angle of zero, only EZNEC's far field analysis reports
it as zero, because (as the manual explains, and as I've explained here
several times before) the far field results are valid at a distance
beyond the point where the surface wave has decayed to essentially zero
-- a few miles at HF. And at that distance, the field at zero elevation
angle is zero if the ground conductivity is finite. If the surface wave
strength is wanted, it can easily be found using EZNEC's near field
calculation, which calculates the total field at any point in space --
including just above the ground surface.

It is of no use in the
prediction of often-used ground waves between stations.

Unless you use the near field results, which do give an accurate
indication of the field at any point in space. I assume you've just
forgotten the several times I've explained that to you. Maybe this will
be the magic time it'll sink in.

Whenever a resistive ground is involved, programs like Eznec do not
produce the true radiation pattern of an antenna. . .

For sure, the modeling of ground is the weakest point of all antenna
modeling programs including EZNEC. But the pattern is generally a good
representation of reality. Remembering, of course, that the far field
pattern is just that -- the pattern at a distant point at which the
surface wave has decayed to zero.

A graphical pattern which includes the surface wave component would be
different at every distance from the antenna up to the distance where
the surface wave has decayed to essentially zero (a few miles at HF).
The field strength at angles greater than zero would be of little
interest to amateurs doing local communication by surface wave. Those
who want to know the field strength at ground level at any distance can
easily get this information from EZNEC's near field analysis (which
reports the total field, not just the near field).

Most amateurs who are interested in local communication over a few miles
using surface waves don't need to see the overall elevation pattern, and
they can get numerical results of the surface field strength from the
near field analysis. Amateurs communicating by sky wave, by far the more
common situation, can benefit from the graphical results afforded by
EZNEC's far field elevation pattern.

Not that there is
anything incorrect with Eznec. It is just the confusing description
of what it displays.

It's interesting that in the 15 years EZNEC and its predecessor ELNEC
have been available, and the thousands of users, no more than a half
dozen people have expressed any confusion regarding its far and near
field analysis. And none of the others has required repeated
explanations. But some people are sure to have more trouble with the
concept than others.

It's explained in the EZNEC manual, and I always welcome questions and
suggestions which would help me make it more clear. I am, however,
resigned to the fact that some small number of people aren't capable of,
and some simply aren't interested in, understanding.

Because of your deep interest in surface wave propagation and field
strength prediction, and your characterization of it as "often-used",
you must do a lot of communication by this mode. What bands do you use,
and what sort of range do you reliably communicate over? How many hams
are within this radius whom you talk to?

Roy Lewallen, W7EL