See Richard's quoted table below.
Various combinations of the answers to questions below could invalidate the
conclusions Richard draws from those figures, or concretely establish them.
** What was the station and location? This allows us to view the location
ourselves with Goggle Earth and other tools.
** What frequency were they operating on? We need wavelength to determine
distance for full formation of far field effects.
** How tall was the radiator? We also need this to determine distance for
full formation of far field effects. On the low end of the BC band, 500
feet is barely above the top of a quarter wave radiator.
** What distance were they with respect to the antenna? Location #12 is
some point on a plot. How does one find this plot? At ten miles, 500
feet is only 1/2 of one degree. Especially at lower frequencies, going
from zero to half a degree could be entirely attributed to a ground effect.
That effect might have vanished by one degree altitude. How to know?
Descend from the customary operational altitude limit of the helicopter
and get 15 or 20 degrees.
** What was the ground characteristic underneath?
** Has this been done over a variety of ground types at other stations, or
is this the only such measurement you know of?
** What was the topology beneath?
** Were they at sufficient distance from the radiator that all far field
effects had full opportunity to form in half the distance measured? Yes
or no answer here does not suffice.
I would have picked a distance of 10 miles or more and descended from
10,000 feet, or higher depending on the helicopter's customary operational
ceiling, to go from zero to 15 or 20 degrees, and be at a distance that
could not be challenged for non-formation of far field effects, and would
have opportunity to accumulate the effects of real life surface clutter
like trees. This would be accompanied by standing-man-with-meter under the
descent to get the ground reading to relate to the readings at altitude.
The higher angles measured would confirm (or not) predicted radiation at
sky angles, and in any event would establish a measured quantitative
relationship between ground based effects and direct radiation.
Can you refer us to the specific source of this material, where we can
answer some of these questions for ourselves, in their published context?
73, Guy.
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
>
>
> ______________________________**_________________
> Remember the PreStew coming on October 20th. http://www.kkn.net/stew for
> more info.
>
_______________________________________________
Remember the PreStew coming on October 20th. http://www.kkn.net/stew for more
info.
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