On 13 Jan 2007 17:46:15 -0800, "AC7PN" wrote:

I would have to run the wires down the face of the cliff to make one of
those. Using NEC I just don't know how to simulate the ground effects
when the land falls away at a 30-50 degree angle. At one place there
is a 60 ft shear verticle drop. My unterminated beverage off the cliff
headed East works well on receive but it is terrible on transmit.

Beverages aren't supposed to work for transmitting so don't be
discouraged by that. I would think that the ground falling away would
be an advantage. Maybe Roy would care to comment on this, but I'd
just model it using the slope on those wires as if you have a really
high support point on the apex of the vee. Keep in mind that if you
don't terminate the legs of the vee then it will be bi-directional, so
if you're in the San Juans and point that sucker toward Florida you
should do equally well into Asia. Gee, I wish I had your problem! ; )

S.T.W.

Sum Ting Wong wrote:
On 13 Jan 2007 17:46:15 -0800, "AC7PN" wrote:

I would have to run the wires down the face of the cliff to make one of
those. Using NEC I just don't know how to simulate the ground effects
when the land falls away at a 30-50 degree angle. At one place there
is a 60 ft shear verticle drop. My unterminated beverage off the cliff
headed East works well on receive but it is terrible on transmit.

Beverages aren't supposed to work for transmitting so don't be
discouraged by that. I would think that the ground falling away would
be an advantage. Maybe Roy would care to comment on this, but I'd
just model it using the slope on those wires as if you have a really
high support point on the apex of the vee. Keep in mind that if you
don't terminate the legs of the vee then it will be bi-directional, so
if you're in the San Juans and point that sucker toward Florida you
should do equally well into Asia. Gee, I wish I had your problem! ; )

S.T.W.

NEC is of course limited to perfectly flat ground of infinite extent. If
the ground slope is constant for a great distance, you can simulate it
by tilting the antenna model the opposite direction then tilting the
resulting pattern. But that's about all you can do. I still use Brian
Beezley's TA program for analyzing the effects of non-flat ground, but
it's long been unavailable and I don't know of any program since which
does the same thing.

Roy Lewallen, W7EL

Roy Lewallen wrote:
NEC is of course limited to perfectly flat ground of infinite extent.
If the ground slope is constant for a great distance, you can simulate
it by tilting the antenna model the opposite direction then tilting the
resulting pattern. But that's about all you can do. I still use Brian
Beezley's TA program for analyzing the effects of non-flat ground, but
it's long been unavailable and I don't know of any program since which
does the same thing.

N6BV's HFTA program is supplied with all recent ARRL Antenna Books, and
is updated and improved in each edition. For anyone who doesn't live on
perfectly flat ground of infinite extent, HFTA can provide a lot of
answers to the old question: "How good is my QTH?"

However, HTFA is limited to horizontal antennas, and I don't know of any
program that does the same for verticals (it's a much more difficult
problem).


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek