Art, K9MZ wrote:
"---radiation angles specifically for 160 meters.
1. How is it measured?"

In degrees above the horizon. It`s geometrical. The effective height of
the reflecting layer above the earth has been observed for a long time
and can be predicted with some accuracy, based upon location, time,
solar radiation, etc.

The angle of incidence is equal to the angle of reflection to a
reference normal to the reflecting plane. So, low angles serve for long
distances between stations, and high angles for short distances that are
too distant to be reached by the groundwave.

Capt. Paul H. Lee, USNR, K6TS has a chart of degrees above the horizon
versus distance to the first reflection zone (a single hop) on page 11
of "Vertical Antenna Handbook", a "CQ" publication. As the height of the
latyer is variable, this is an approximation based on probabilities.

A 5/8-wave vertical gives optimum low-angle radiation between 3 and 27
degrees. The latter angle gets you out to about 500 miles. Lower angles
get you out to about 2000 miles on one hop.

Vertical antennas work with vertically polarized waves. Once the wave is
reflected by the ionosphere, polarization of the reflection is more or
less random.

"2. What is the angles per percentage of contacts?"

Depends on where your station is in respect to the majority of stations
you want to contact.

"3. Are they all horizontally polarized when subject to skip?"

No. The ionosphere does not care what the wave polarization is. It will
reflect whatever strikes it at various polarizations. It won`t maintain
polarizations! You can receive via the ionosphere almost equally well,
on average, with any polarization regardless of what was transmitted.
Noise reception is likely worse using a vertical receiving antenna.

"Tom stated on this newsgroup that a horizontal dipole at 1/2-wavelength
was inferior to his other antennas---."

Can`t argue with Tom`s observation about his antennas, but it does not
correspond with most observations of horizontal antenna performance when
you have a resonant dipole at 1/2-wave above the earth. Look at Fig 12-D
on page 3-11 of the 19th edition of the ARRL Antenna Book. Maximum
radiation is at 30-degrees above the horizon. From Capt. Lee`s diagram,
that would get you stations as close as 500 miles, and beyond 1000 miles
due to the range of strong elevation angles in the pattern.

I don`t know what Ton`s problems are but suspect that he ignores some of
the ground effects. He has expressed dissatisfaction with his verticals
too.

Vertivcals in particular are sensitive to good earth under and around
the antenna.

Horizontal polarization isn`t bad for HF. Most of the world`s HF
commercial stations use horizontal antennas for skywave propagation.

Best regards, Richard Harrison, KB5WZI