On Thu, 10 Feb 2005 03:49:58 GMT, Rick Frazier
wrote:

I'm thinking I can set the angle of radiation for a horizontal dipole,
by hanging it the proper distance above (and or towards or away from the
desired direction) to essentially add to the desired angle of radiation,
if only by some small amount.

Hi Rick,

This is true, but probably not for the reasons you may have
envisioned. Simply put, the metal acts as a shield to prevent loss to
ground. What is not lost is radiated in other directions. It aids in
those directions straight up, but it also aids in directions at every
other angle too - net result: better signal; how much: nothing
dramatic. This simple fact will probably get you more initial gain
than you will add doing anything further (short of building a tower
and putting up a beam).

Is there an optimum angle of radiation for DX,
Yes - you may hit it poorly tho'.


Though optimizing the location of the dipole for a particular angle of
radiation seems good, there will also be a corresponding cancellation of
signals at other (calculable) angles of radiation, right?
Odds are that given this vague description, that, yes, anything could
happen. Guessing your intent, well you are already in illusionland
with optimization - unless, of course, 1dB optimizations light up the
stars in your firmament.

Is it all for naught anyway? Given the action of a wire reflector, will
the sheet metal slab only look like a larger version and only in the
general direction perpendicular to the center of the sheet metal axis?
Practical answer is no one will probably notice even if you could
shift everything around to suit your best guess. You have far more
dramatic opportunities (more than 1dB) with a vertical within sight of
the ocean.

73's
Richard Clark, KB7QHC

Angle of Radiation - Hawaii
 

Hello:

I live in Hawaii, the land of metal roofing, and got to thinking on the
way home tonight, that instead of complaining about it, I may be able to
put the metal roof to some sort of advantage with regard to DX
communications.

I'm thinking I can set the angle of radiation for a horizontal dipole,
by hanging it the proper distance above (and or towards or away from the
desired direction) to essentially add to the desired angle of radiation,
if only by some small amount.

Think of the roof as an rf mirror about 60 feet long and 20 feet wide.
Pitch is about 5 inches per foot, so it's a relatively low slope. A
wire (source) located perpendicular to and centered on the
roof/reflector would be a pretty high angle of radiation. Of course,
the distance from the reflector to the dipole would want to be an
optimum distance so it reinforces the signal instead of cancels it.
One would think that this high angle of radiation should be able to be
changed (shifted lower) by moving the dipole away from the desired
direction of radiation. Of course, I would expect only a relatively
small portion of the signal is actually affected this way, because the
reflector is only a relatively small percentage of 180 degrees... Or,
maybe not... A wire dipole, with a wire reflector behind it does
increase gain in the forward direction, and the wire reflector is only
an extremely small portion of the nearly 180 degree arc behind the
driven element.

OK, now comes the fun part. There are (at least) three questions:

Is there an optimum angle of radiation for DX, (lower is better, to a
point?) given that I'm 2300+ miles from the nearest land, and may be
most interested in locations half way 'round the world and not just the
nearest land, (which I can talk to just fine right now, thank you)?

Though optimizing the location of the dipole for a particular angle of
radiation seems good, there will also be a corresponding cancellation of
signals at other (calculable) angles of radiation, right?

Is it all for naught anyway? Given the action of a wire reflector, will
the sheet metal slab only look like a larger version and only in the
general direction perpendicular to the center of the sheet metal axis?

I've gone and done it now, got myself questioning more than I thought I
knew... How 'bout you? Got any opinions?

Thanks
-_Rick