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)