Topband: Anyone purchased the ARRL book on Short Antennas for160???
rfry at adams.net
Fri Jan 24 07:07:03 EST 2014
Guy Olinger wrote:
>...the presentation shows the max of the four elevated at *minus* 1.17,
>while the buried radials are minus 0.71. That means the 4 elevated are
>about a half dB inferior to dense buried.
The text of my post first including the URL for my NEC study (link below)
stated that there was about 0.5 dB difference between them because I hadn't
taken the time to trim the monopoles heights slightly to produce identical
results. But that wasn't necessary to make the point that the system with
elevated radials installed over poor earth having no buried radials in it
has essentially the same performance as the system using 120 x 1/4-wave
radials (only), buried in that same earth.
>Did you run that four elevated model setup with the buried radials in
>place, but not connected to the feedpoint, just "floating", or was it just
>four elevated over plain ground.
The elevated system was comprised of five conductors, only: the vertical
monopole and the four horizontal radials -- as per the wire model shown as
an inset in the elevation pattern for the elevated system in my graphic.
That elevated system has no metallic connection to the earth, and no other
metallic conductors in the model.
>What were the ground constants in use when you ran the models?
As stated in my earlier post linked below, and also in large letters at the
top of my NEC study page, it was 1 mS/m, d.c. 5.
>When you say "closely replicates", are you comparing the models' groundwave
>display to field strength measurements at ground?
The inverse distance field intensity for 1 kW of applied power at a distance
of 1 km determined by the consultant for WPCI's elevated system closely
replicates the inverse distance field expected by the FCC for a 1/4-wave
monopole driven against 120 x 1/4-wave buried radials (302 mVm and 307 mV/m,
respectively). A perfect 1/4-wave monopole driven against a perfect ground
plane produces about 313.6 mV/m at 1 km for 1 kW of applied power.
My NEC study shows that the peak gain and radiation pattern of the two
systems compared essentially are duplicates. Equal antenna system gains
produce equal fields at a given distance, for a given applied power.
Note that the basic information needed to answer the questions shown above
already was included in my earlier posts.
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