Hi Richard,

On 8 jun, 13:41, "Richard Fry" wrote:
One exception being the typical MW broadcast monopole vertical used with
120 buried radials, each 1/4-wave or more in length. This configuration
produces its maximum radiation in the horizontal plane (ie, zero degrees
elevation). If this was not true, then AM broadcast stations would have
very few daytime listeners.

Day-time listening does not require maximum radiation at 0 deg.
elevation, but does require radiation at 0 deg elevation. So at that
point I thing you should reconsider your statement.

The ground wave fields 0.3 mile from such antenna systems have been
accurately measured as far back as 1937 by Brown, Lewis and Epstein of RCA
Labs, and for a vertical radiator of 60 to 90 degrees in height shown to be
within a few percent of the peak, free-space field produced by a 1/2-wave
dipole, at the same tx power. The frequency used in this set of tests was 3
MHz.

I especially mentioned "short wave communication" and "average soil"
to exclude the AM an LW broadcast propagation. In that case the pseudo
Brewster angle can be that low, that (near) fields form the ground
current do not cancel the direct field from the vertical radiator.

Ground wave propagation loss including earth curvature will cause the
h-plane field from these verticals to go to zero beyond some distance* from
the transmit antenna site, but that does not mean that zero h-plane field
was "launched" by this vertical radiator in the first place.

*and that distance can be over 200 miles for a high power AM station on a
low frequency

I agree that vary close to the transmitter (you are in the transition
field zone), the field strength will behave as over a perfect
conducting ground plane.

There is another sign that even an AM broadcast station does not have
maximum radiation at 0 deg. elevation. When you check your field
strength (E or H) graphs up to 60 miles (where earth curvature can be
neglected) you will notice that the field strength falls of faster
then with 1/distance. That would not be the case when max radiation is
at 0 deg. elevation.

My information shows 20 dB below 1/r (1 MHz, 100km, "good ground"),
41dB below 1/r (1 MHz, 100km, "good ground"), source: "The services
textbook of radio, 1958, volume 5 page 442. For average soil, and
especially rocky like ground, the field strength will be significantly
lower.

Probably your material does also treat "height gain factors" Then you
will see that above a certain height, field strength increases with
increasing height (indication of more gain under that elevation).

Best regards,

Wim
PA3DJS