In <199705010118.VAA21435@dayton.akorn.net>, on 04/30/97
at 05:30 PM, Ed Goodman <n5nug@ix.netcom.com> said:
>Tom, in all of your wisdom and antenna experience, please tell me what
>the field strength in millivolts per meter should be for a 31' tall
>vertical antenna that is excited at 1 KW as read at 1 kilometer. This
>is taking into consideration a good radial system.
If you're going to bait someone ask a question with sufficient data to get a
valid answer. In this case, either specify a frequency or the vertical height
in wavelenghts.
However, the following is taken from an article by Carl Smith of Carl Smith
Electronics, 8200 Snowville Rd., Cleveland, OH 44141, in the NAB Engineering
Handbook, 8th Edition, page 188, figure 2 (caption: Quantitative vertical
radiation pattern mV/M unattenuated field at one kilometer for one KW):
antenna height unattenuated field @ 1 KM
-------------------------------------------------------------
spehrical isotropic 173.2 mV/M
hemispherical isotropic 244.8 mV/M
infinitessimal monopole 299.8 mV/M
90 degrees 313.6 mV/M
180 degrees 380.1 mV/M
225 degrees 439.3 mV/M
Further, the article says:
> Electrically short towers are inefficient radiators, not only because
> of the shape of their vertical radiation characteristics as shown in
> figure 2, but also because of proportionally higher ground losses.
> For example, a tower 48 degrees high with a base resistance of only
> 9 ohms will have approximately 10% of the available power wasted in
> ground system resistance losses (typically about 1 ohm).
The "typical" ground system referenced in the article is defined on page 190.
> A system of 120 radia ground wires, each 90 degrees long (140 degrees
> is considered optimum), and equally spaced out from the tower base,
> consititutes a "standard" ground system. This is often augmented with
> an additional 120 interspersed radials 50 feet long of an expanded
> copper mesh ground screen 25 to 50 feet square centered at the tower.
In case you don't know of Carl Smith, he is considered one of the pre-eminent
consultants in the field of AM antennas and directional arrays.
73,
... Joe Subich, W8IK ex-AD8I
<W8IK@ibm.net>
<jsubich@ibm.net>
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