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. An antenna which radiates its maximum at a high angle might well
radiate more at a low angle than an antenna with a lower angle of
maximum radiation.

Roy Lewallen, W7EL

wrote:
On 13 Sep 2005 16:15:08 GMT, "Bill Turner" wrote:

Without more information, this comparison is flawed. A mobile whip has
a lower angle of radiation than a horizontal dipole. . .

Correct on radiation angle . . .

On Tue, 13 Sep 2005 20:43:23 -0700, 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. An antenna which radiates its maximum at a high angle might well
radiate more at a low angle than an antenna with a lower angle of
maximum radiation.

Roy Lewallen, W7EL

Hello Roy,

I do understand that. I also understand when you say radiation angle
your talking about the primary or dominent lobe(s). There may be
many other lobes at useful or less than useful angles present as well.

However, how does that relate to using a shortend antenna with maybe
10% radiation efficientcy to a dipole at a reasonably attainable
height?

Allison
KB1GMX


wrote:
On 13 Sep 2005 16:15:08 GMT, "Bill Turner" wrote:

Without more information, this comparison is flawed. A mobile whip has
a lower angle of radiation than a horizontal dipole. . .

Correct on radiation angle . . .

However, how does that relate to using a shortend antenna with maybe
10% radiation efficientcy to a dipole at a reasonably attainable
height?

Well....Exactly as he described.
An antenna which radiates its maximum at a high angle might well
radiate more at a low angle than an antenna with a lower angle of
maximum radiation.

The thing is "might".... My mobile antenna on 40m is *much* less
efficient than my dipole at 40 ft. But...It still is the best to longer
hauls over about 800 miles, and to dx. In it's case, it does radiate
more at the lower angles I'm using at that time, vs the dipole.
With some lesser mobiles, "mine is fairly stout", this might not be
the case. The best antenna should always be decided to fit the
usual paths to be used. In the case of my mobile vs the dipole, it's
possible that if the dipole were raised another 1/4 wave higher, it
could match the mobile at those lower angles.
At home, I often ran a dipole at 40 ft vs a full size ground plane at
the same height. Both were pretty efficient. Efficiency comparisons
were fairly useless as to actual performance. What really decides
which is best at a given time, is the path, and angles to be used.
Now, if you compare two same length low dipoles, both to NVIS, both
shooting straight up, and one is less lossy than the other as far as
feeding method, etc, then yes, efficiency will decide which one is
best.
MK

wrote:
On Tue, 13 Sep 2005 20:43:23 -0700, 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. An antenna which radiates its maximum at a high angle might well
radiate more at a low angle than an antenna with a lower angle of
maximum radiation.

Roy Lewallen, W7EL


Hello Roy,

I do understand that. I also understand when you say radiation angle
your talking about the primary or dominent lobe(s). There may be
many other lobes at useful or less than useful angles present as well.

However, how does that relate to using a shortend antenna with maybe
10% radiation efficientcy to a dipole at a reasonably attainable
height?

Allison
KB1GMX

The context was that one antenna was better for DX than the other
because it had a "lower radiation angle". An antenna with a "low
radiation angle" which is 10% efficient probably radiates less at low
angles than a more efficient antenna with a "high radiation angle".
Therefore it's not a better DX antenna. My point is simply that the
angle of maximum radiation is not a valid criterion for comparing antennas.

Roy Lewallen, W7EL

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

A better indication would be a
graphical representation.

The EZNEC demo does that well. There is a little green ball
that you can grab with your mouse, and place it at any angle
you wanna check. Makes it quite easy to see, or compare
various angles. MK

wrote:
A better indication would be a
graphical representation.

The EZNEC demo does that well. There is a little green ball
that you can grab with your mouse, and place it at any angle
you wanna check. Makes it quite easy to see, or compare
various angles. MK


Better yet, you can superimpose the plots from two antennas for direct
comparison. In v. 4.0, you can even get a numerical readout of the
difference between the two in dB at the angle of the cursor (the little
green ball).

Roy Lewallen, W7EL

Bill Turner wrote:
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

I agree, which is why EZNEC produces a graphical output. I encourage
people to look at it rather than reducing the pattern to a single
number. And I have to emphasize once again that what really counts is
the field strength, not the pattern shape. An antenna can have a
wonderful looking pattern with nearly all its radiation at low angles,
and still be a poor antenna for DX. Or with nearly all its radiation at
high angles and be a poor antenna for short range communications. One
familiar example is a Beverage antenna, which has a lovely pattern shape
but makes a poor transmitting antenna. A quarter wave vertical will
nearly always do much better for transmitting, even at the angles
favored by the Beverage.

Roy Lewallen, W7EL

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

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