Topband: Monopole Elev Pattern w.r.t. Earth Conductivity

[Richard Fry]

from [Tom W8JI]:
>The issue here is one of measurement distance and the assumed flat earth, 
>and how much the ground wave contributes to low angle radiation. We 
>obviously know radiation at zero degrees is not zero, as distant models 
>show.

As to measured data, below with his permission is a quote from a broadcast 
consultant acquaintance of mine who has made helicopter measurements of the 
elevation patterns of MW monopoles. These data below were taken using a 
helicopter at a horizontal distance of 2.8 km from the monopole, showing the 
fields existing at elevation angles of zero to about 3 degrees above the 
horizontal plane.

This path length is short enough so that earth conductivity has little 
bearing on the measured fields, but not so short that the intrinsic, 
~cosine-shaped elevation pattern of a 1/4-wave monopole will significantly 
affect the fields at those measured elevations.

It will be seen from the data that no "notch" exists in the fields radiated 
by the monopole at elevation angles of 3 degrees and less, as expected by 
some when considering only the far-field patterns shown by MoM (NEC) 
software, and in antenna textbooks.

That low-angle radiation is a space wave, not a ground wave, and given the 
right conditions it can reach the ionosphere to produce a sky wave.   That 
sky wave can be very useful to hams using vertical monopoles, even though 
its existence may not be recognized.

QUOTE

Helicopter Vertical Calibration

To check for variations in field intensity due to elevation above ground, we
hovered over one location and rose from the ground at 50-foot intervals to
500 feet.  Location #12 on the 230° radial was used (non-directional mode),
and the data as presented below shows no significant effect.  Measurements
taken for this report were done at an average elevation of 500 feet and the
calibration of the meter takes the vertical factor into account.

Height above ground      Field Intensity       Variation from 0 feet
 0                                  56 mV/m                    (Ref.)
50                                   56                          +0.0 mV/m
100                                  56                           +0.0
150                                  55                            -1.0
200                                  55                            -1.0
250                                  55                            -1.0
300                                  55                            -1.0
350                                  54                            -2.0
400                                  54                            -2.0
450                                  54                            -2.0
500                                  54                            -2.0

Averages:               54.91 mV/m               -1.09 mV/m (-1.99%)

END QUOTE