Topband: Anyone purchased the ARRL book on Short Antennas for160???

[Joe Subich, W4TV]

It would be interesting to see the same modelling over nonconductive
"rock" earth.  I suspect once the soil gets bad enough that there is
essentially no electron mobility the "ground plane" (elevated radials)
antenna begins to act as if it was in free space - or at least a
substantial fraction of a wavelength above the ground - which can
reduce ground losses substantially due to the reduction of fields in
the soil.

While 1 km field readings are interesting, 1 km is only 6 wavelengths
at 160 meters (and less in the AM band) so those values still contain a
strong "near field" component and do not adequately reflect the true
ground losses.  If one wants to really measure ground losses, it takes
at least two readings - one at 1 mile (~10 wavelengths) and another at
1.4 miles or 2 miles *along the same radial*.  The departure from
square law losses can be attributed to additional ground losses.

Although 1 and 1.4/2 mi field strength specifically measures groundwave
losses, the soil conditions should be homogeneous enough in the skywave
launching region that the ground wave case will provide far greater
accuracy than any modelling.  The problem is that accurate measurement
of field strength is difficult - particularly in urban/suburban areas -
and nobody wants to take the time to do it unless they are required to
do so.  Even the AM broadcasters take pains to select monitoring points
well away from "clutter".

73,

    ... Joe, W4TV


On 1/23/2014 12:05 AM, Mike Waters wrote:
> A very respected authority on radial systems, Rudy Severns N6LF, has this
> to say about 4 elevated radials:
>
> "Since my QST article I've done some modeling to explore the sensitivity of
> a simple 4-radial system to asymmetries in the radial fan. The modeling
> easily replicates Weber's results and the news is even worse than Dick
> thought! The 4-radial system is indeed very sensitive to quite small
> irregularities and/or nearby conductors. It's easy to demonstrate pattern
> distortions of 2-3 dB and increased ground losses of 1-2 dB and these are
> by no means worst cases. More importantly, the modeling shows that as the
> number of elevated radials is increased the sensitivity goes down quickly.
> Elevated systems with 10-12 radials are not very sensitive to reasonable
> asymmetries. It turns out that a number of hams have observed significant
> improvements in their elevated systems by going to 10 or more radials. Both
> modeling and
> experiment seem to agree.
>
> "I doubt that the average 4-radial system is actually performing as
> "advertized". No doubt there are exceptions but the advice I presently give
> is to use 10 or more radials whenever possible in an elevated system."
>
> (From
> http://rudys.typepad.com/files/december-2010-letter-to-qst-technical-correspondence.pdf
> )
>
> See http://www.antennasbyn6lf.com/
>
> 73, Mike
> www.w0btu.com
>
>
> On Wed, Jan 22, 2014 at 7:18 AM, Richard Fry <rfry at adams.net> wrote:
>
>> C. Cunningham wrote:
>>
>>> If you get up to 4 symmetrical elevated radials there's not much to be
>>> gained by adding more. There's been a lot of work done in the broadcast
>>> industry using elevated radials to replace deteriorated buried radial
>>> fields that shows that pretty clearly. It was published in some IEEE
>>> transactions some years ago.
>>>
>>
>> Probably this refers to the paper of Clarence Beverage titled "NEW AM
>> BROADCAST ANTENNA DESIGNS HAVING FIELD VALIDATED PERFORMANCE."  It is
>> available as a PDF download from http://www.commtechrf.com/downloads.asp .
>>
>> Below is a quote from that paper showing that the __measured__ groundwave
>> field at 1 km radiated by a base-insulated, 1/4-wave vertical using four
>> elevated radials was within 0.14 decibels of that from a perfect 1/4-wave
>> vertical monopole driven against 120 x 1/4-wave buried radials.
>>
>> The r-f loss resistance of 120 x 1/4-wave buried radials used in a
>> monopole antenna system typically is less than 2 ohms in the MW and low-HF
>> bands, regardless of the conductivity of the earth in which they are
>> buried.  The use of four elevated 1/4-wave radials in this system produced
>> almost identical performance to using a full set of 120 x 1/4-wave buried
>> radials.
>>
>> "The first permanent use of an elevated radial ground system appears to be
>> at WPCI, 1490 kHz in Greenville, South Carolina. This installation,
>> designed by William A. Culpepper, involved replacing a standard buried
>> system with a four wire elevated system consisting of #10 solid copper
>> wire, one quarter wave in length, and supported on treated wooden posts
>> which keep the radials 4.9 meters above ground. The antenna radiation
>> efficiency, based on field strength readings on the eight cardinal radials,
>> was 302 mV/m at 1 kilometer versus the predicted FCC value of 307 mV/m. The
>> WPCI installation was unique in that the tower was base insulated but the
>> radials came right up to the tower, 4.9 meters above ground and terminated
>> in insulators. The tower was fed from the tuning unit, through a piece of
>> coax to the 5 meter point on the tower where the center conductor of the
>> coax was attached to the tower and the shield to the elevated radials. This
>> feed system resulted in a higher feed resistance than would normally be
>> expected. Data on this facility was taken from the FCC files."
>>
>> Guy Olinger wrote:
>>
>>> Be careful not to extrapolate very specifically qualified broadcast
>>> experience into ham radio. Originally FCC spec radials still make the close
>>> foreground earth appear VERY conductive, which is NOT an advantage one will
>>> have putting up two or four radials over plain old dirt, unless one is
>>> talking about midwest USA 30 millisiemen super dirt.
>>>
>>
>> A monopole system using ~ four evenly spaced, horizontal, elevated radials
>> or an "FCP" does not need (or use) a highly-conductive region ("FCC spec
>> radials") around the base of the vertical radiator, because in such antenna
>> systems the r-f currents flowing on its vertical and horizontal wires to
>> produce radiation do not travel through the earth.
>>
>> Note that the system described in the quote from Clarence Beverage's paper
>> (above) was installed/tested near Greenville, South Carolina -- a region
>> having earth conductivity of not more than 4 mS/m per the FCC M3
>> conductivity map, and probably less than that.  Yet it produced almost 100%
>> radiation efficiency as measured by a broadcast consulting engineer using a
>> calibrated field intensity meter.
>>
>> Such characteristics would apply to the use of elevated radial systems by
>> ham radio operators as well as they do for AM broadcast stations.
>>
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