Topbanders
Paul's email provides some good 'food for thoughts' (see original email
below). To me it looks that to measure a low angle radiation (say 10 dgrs)
field strength at 1km distance from the vertical radiator, the sense antenna
needs to be at 176m height from the ground surface (calculation based on
using right triangle formula and assumes that a small magnetic loop sense
antenna would be used as per N6LF field strength experiments).
Any ideas as to what other sense antenna could be used for the low angle
radiation field strength measurements beyond the near field zone, which
would not require an impossible antenna placement height? How can we be sure
that (at least most of ) the field 'visible' to the sense antenna is namely
in the desired radiation angle range, say 8 to 12 dgrs if the sense antenna
is placed on the ground? In other words, if we use a low dipole for a sense
antenna, how can we extrapolate the percentage of the desired low angle
radiation field strength from the overall field strength that the sense
antenna will see?
It seems that N6LF used small magnetic loop antenna as it can 'see' equally
well over a wide range of radiation angles and the idea was to possition the
sense antenna at such a distance and height from the source that it would be
'physically' possitioned in about 8 dgr radiation area (the distance and the
height as used in N6LF 40m experiment in the right triangle formula results
in (if I remember correctly) 8 dgrs radiation angle to be 'visible' the the
sense antenna).
Any comments/ ideas as to what other 'sense' antenna could be used for the
low angle radiation field strength measurement at the far field zone which
would only 'see' desired range of radiation angles?
73 de VK2CCC
Tomas
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If FS measurements are taken at say 1 km from the radiator, variances in
ground conductivity over a 1 km path must also affect the shape of the
vertical profile. Testers who are making these measurements within a few
hundred feet of the radiator seem to be missing this and are drawing the
conclusion that the profile does not change when they are taking FS
measurements inside the lobe of the profile. Measurements taken too close
to the radiator will not reveal changes in low-angle radiation. So, it
seems to me that any performance tests that include low angle of radiation
(less than 5-10 degrees), needs to be taken at some far distance from the
radiator.
Paul, W9AC
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