hey W8JI
 

why do dislike 5/8 wave antennas? can you point me to any references. i
realize there is a high lobe.

i have an old Low Band Dxing, and ON4UN seems to like 5/8 on 40. i
personally tried a 5/8 vertical on 10 with bad results. however, my ground
system was terrible.

i plan to try 5/8 with full 120 * 1/2 wave radials.

i remember at one multi-single, we had a 1/4 wave 10 meter at 100 feet that
was even with the beams sometimes.

i believe K3LR mentioned he was building a 10 meter 5/8 wave 4 square. was
he kidding?

Gravity

hey W8JI
 

one thing i've been pondering is a vertical colinear. 1/2 wave over 1/2
wave. i have not modeled it.

is there any free modeling software?

i noticed that you stated that phased arrays with elements separated by more
than 2 waves don't work well. i was thinking of a vertical array, either
inline or broadside.

Gravity

hey W8JI
 

just some random thoughts:

a ground system for 10 meter 4-square would be 240 waves worth of wire
(minus some because of shared radials). that's 8000 feet, at 5 cents a
foot, $200. you can set up a beam at 30 feet for that price.

scaling up to 40 meters, that's a lot of wire.

Gravity

hey W8JI
 

4NEC2?

http://home.ict.nl/~arivoors/Home.htm

Cheers Bob VK2YQA

gravity wrote:


is there any free modeling software?

hey W8JI
 

gravity wrote:
one thing i've been pondering is a vertical colinear. 1/2 wave over 1/2
wave. i have not modeled it.

is there any free modeling software?

You can use the free demo copy of EZNEC by driving the
collinear with two sources and varying the phase angle
between them. Then you can design an appropriate phasing
network. I don't think the lumped inductive reactance
available in EZNEC will yield an accurate phase shift
and the free demo will not handle enough segments to
model a helical coil.
--
73, Cecil http://www.qsl.net/w5dxp

hey W8JI
 

gravity wrote:
just some random thoughts:

a ground system for 10 meter 4-square would be 240 waves worth of wire
(minus some because of shared radials). that's 8000 feet, at 5 cents a
foot, $200. you can set up a beam at 30 feet for that price.

Or how about a 10m rotatable EDZ? No radials required.
--
73, Cecil http://www.qsl.net/w5dxp

hey W8JI
 

gravity wrote:
why do dislike 5/8 wave antennas? can you point me to any references. i
realize there is a high lobe.


Anyone who understands how a 5/8th wave works, and who isn't captivated
by the popular fantasy that the length makes the gain, would know what
the problems are.

A 5/8th wave antenna gets its gain from the ground reflection. The
ground reflection is what form the "image" that produces the gain.

Unless the ground is very large and flat and highly conductive, the
5/8th wave antenna concentrates most of its energy at high
angles.....not along the ground.

Move the 5/8th wave up above the ground or use a poor ground, and
maximum low angle FS comes from shorter antennas.

If you look at:

http://www.cebik.com/gp/58-1.html

you will see a 5/8th wave on 80 meters with a large flat ground system
not only gives marginal gain over a 1/4 w, it also has a null aat the
most useful wave angles for most work.

If you elevate the 5/8th wave or take away the good ground system, the
very small advantage it has goes away.

As a matter of fact AM BC stations, despite their large ground systems,
abandoned the 5/8th wave many years ago. They found in the real world
use of 5/8th waves instead of extending coverage they reduced coverage.

73 Tom

hey W8JI
 

W8JI,

thanks for your comments. i must have missed that cebik article, so i will
read it.

now i reread the antenna section of ON4UN's book, and he does say 5/8 wave
are best for very poor or very good (sal****er) ground. so i am probably
wasting my time with 5/8 waves, although i will try it for the hell of it.

i bet ON4UN used a 5/8 on 40 because he needed the length for 160 and 80 in
the multiband vertical.

hmm.

Gravity

hey W8JI
 

"Cecil Moore" wrote in message
. com...

Or how about a 10m rotatable EDZ? No radials required.

this is a good idea. cebik site has some articles about EDZ beams and
colinears and arrays.

i should probably go with a 4 element 10 meter Yagi, but i want to
experiment with some alternatives.

Gravity

hey W8JI
 

"Bob Bob" wrote in message
...
4NEC2?

http://home.ict.nl/~arivoors/Home.htm

thanks Bob. that looks like it may do the trick.

Gravity

hey W8JI
 

"Cecil Moore" wrote in message
om...
gravity wrote:
one thing i've been pondering is a vertical colinear. 1/2 wave over 1/2
wave. i have not modeled it.

is there any free modeling software?

You can use the free demo copy of EZNEC by driving the
collinear with two sources and varying the phase angle
between them. Then you can design an appropriate phasing
network. I don't think the lumped inductive reactance
available in EZNEC will yield an accurate phase shift
and the free demo will not handle enough segments to
model a helical coil.
--

thanks, that plus the program Bob mentioned may get me started in modeling.

Gravity

73, Cecil http://www.qsl.net/w5dxp

hey W8JI
 

As a matter of fact AM BC stations, despite their large ground
systems, abandoned the 5/8th wave many years ago. They
found in the real world use of 5/8th waves instead of extending
coverage they reduced coverage.
____________

The h-plane inverse field of a 5/8-wave AM BC vertical working against 120
buried radials each at least 1/4-wave long is calculated in theory and
measured in practice as having the greatest possible field per unit of
radiated power of any non-sectionalized radiator height, no matter what the
earth conductivity at the antenna site.

But the 5/8 wave BC vertical does have a discrete, high angle sidelobe that,
at night, can interfere with its own groundwave over an annular zone
starting a few hundred miles from the antenna. Very distant coverage is
provided by low-angle skywave (less than about 30 degrees), and is not
affected because the groundwave is gone at those distance ranges.

But this is the reason that 24-hr, 50 kW AM BC stations use a radiator
typically around 195 degrees. Its h-plane inverse field (the groundwave) is
not quite as great as from a 5/8-wave, but it doesn't develop that
high-angle lobe. It is popularly called an "antifade" radiator.

RF (WJR staff engineer, 1960s)