Topband: Modeling "Ground" and losses

[Guy Olinger K2AV]

Having lived in the Newburgh area, I have to object again to this report
that I have tried to debunk before. I have earlier communicated this
objection to Mr. Fry which he chooses to ignore.

Given the topography of the area, this report is simply incomplete and
unproven unless the GPS coordinates are provided and it is firmly known
whether the antenna was at the Hudson river plain level or on one of the
500-1000 foot HAAT hills in the area. Then one would need to know the GPS
coordinates of all the data points to evaluate terrain influences along the
path.

As every ham can tell you, with 80 accumulated years of worldwide
irrefutable data only improved upon by transmission over salt water, high
hilltop to high hilltop has exceptional overall propagation advantages. I
continue to wonder about this report as a possible "con job" absent
sufficient data, or why a reputable firm would even think to advance this
study without those qualifications supplied with the report.

Simply put, the Newburgh area is at least a difficult area and at worst an
entirely inappropriate area to test this thesis. At other sites, it would
need to be known whether the site is a conversion site, that is, over old
radials. And then it would be necessary to evaluate this concept over
pristine ground vs. over conversion site ground.

The problem with the Newburgh, NY geography is easily seen by anyone with
Google Earth using the slanted view which displays vertical topography as
if viewed from a low flying plane or helicopter, and will clearly show the
area's characteristic sharp transitions between the river plain and
hilltops.

As is irrefutably known to any ham, the propagation from the hilltop sites
is immensely better than inland sites at locally lower ground, especially
for receptors that are themselves at ground.

All-in-all the study is a shame to have been published in this missing data
format. Otherwise it might have been a demonstration of how much loss can
be avoided by elevating the feedpoint.

A far better site for the purpose would have been the New Jersey farming
area flatlands. If THAT delivers the same readings, then you have
something. If it takes hilltops to make hay, there simply is nothing new.

73, Guy.


On Fri, Feb 27, 2015 at 1:35 PM, Richard Fry <rfry at adams.net> wrote:

> Regarding the quotes below:
>
>  2.) We see any radial or counterpoise system, close to the radial or
>> counterpoise, has to have external fields. Those fields must extend out of
>> the counterpoise, and always cause loss when a counterpoise is near a lossy
>> media.
>>
>
>  3.) We see we only mitigate the loss by making current density in the
>> lossy media as low as possible, which generally means spreading the current
>> out as evenly as possible in the lossy media or moving the antenna and a
>> counterpoise away from the lossy media to reduce current.
>>
>
> Please note that vertical monopoles driven against a set of four- or
> six-wire counterpoises are in daily use by several AM broadcast stations in
> the U.S.
>
> These stations provide * measured * fields very close to the maximum
> theoretical field possible from that monopole and applied power when driven
> against a PERFECT ground plane -- even though these counterpoises are
> elevated only some 10 or 15 feet above earth of rather poor earth
> conductivity.
>
> Here is a quote about one of the early cases, from the NAB paper titled
>
> NEW AM BROADCAST ANTENNA DESIGNS HAVING FIELD VALIDATED PERFORMANCE
>   by
> Clarence M. Beverage
> Communications Technologies, Inc.
> Marlton, NJ
>
> \\  In November of 1988, our firm supervised the construction of a
> temporary
> antenna system in Newburgh, New York under FCC Special Field Test Authority
> using call sign KPI-204. The antenna system consisted of a lightweight, 15
> inch
> face tower, 120 feet in height, with a base insulator at the 15 foot
> elevation and
> six elevated radials, a quarter wave in length, spaced evenly around the
> tower and
> elevated 15 feet above the ground. The radials were fully insulated from
> ground
> and supported at the ends by wooden tripods. Approximately ten feet above
> ground, a T network for matching the antenna was mounted on a piece of
> marine
> plywood to isolate the components from contact with the lower section of
> the \
> tower which was grounded. Power was fed to the system through a 200 foot
> length
> of coaxial cable with the cable shield connected to the shunt element of
> the
> T network and to the elevated radials. A balun or RF choke on the feedline
> was
> not employed and the feedline was isolated from the lower section of the
> tower.
> The system operated on 1580 kHz at a power of 750 watts.
>
> The efficiency of the antenna was determined by radial field intensity
> measure-
> ments along 12 radials extending out to a distance of up to 85 kilometers.
> The
> measured RMS efficiency was 287 mV/m for 1 kW, at one kilometer, which is
> the same measured value as would be expected for a 0.17 wave tower
> above 120 buried radials. //
>
> Clearly there is little effect on the radiation efficiency of these
> systems due to the proximity* of their counterpoise to the lossy media of
> nearby earth.
>
>  *about 8.7 degrees, in this case
>
> R. Fry
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
>