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[TowerTalk] RADIAL Questions and Answers

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Subject: [TowerTalk] RADIAL Questions and Answers
Date: Fri, 19 Dec 1997 05:47:56 -0600

>Are insulated wires laid loosely on the ground essentially non-resonant?


>So, for question number two, do I need to tune these insulated  radials 
<laying on top of the ground surface to 1/4 WL at 80M to obtain resonance

<at 3.5 MHz?


>de  Tom  N4KG

When SWR and antenna feedpoint resistance was measured at the base
of a vertical element against a ground rod (4 ft in ground, 4 ft above
minimum SWR and resistance was observed at a frequency  higher  than
expected, using an MFJ-259 antenna analyzer.

 When measured against the radial field of 32 radials mostly around 100
long, the minimum SWR and antenna feedpoint resistance was observed
well below the target frequency using a fanned vertical element
of 144 ft of wire folded in half and spaced 2 ft at the top.

To better understand these readings, the fanned element was lowered and
a single 70 ft wire was pulled in it's place.  Minimum SWR and resistance
was observed at 3.3 MHz when fed against the radial field.

When measured against the ground rod, minimum SWR and resistance
was observed around 4.0 MHz, much higher than would be expected for
a single 70 ft vertical wire.  

I still do not understand why the antenna appears to resonate higher in
frequency when fed against a single ground rod.  When fed against the
radial field of mostly  0.35 WL (wavelength) radials, resonance occurs
in the expected frequency range.

Following this determination, the fanned element was again installed and
cut to resonance at 3.5 MHz with a vertical height of 61 ft and 2 ft
across the
top for a total  FOLDED  wire length of 134 ft.

At resonance, the SWR meter indicated around 1.1 to 1.2 and the
meter read around 31 ohms.  It is believed these readings are slightly

So, these measurements would indicate that radials ARE  essentially 
NON-resonant when laid on the ground and DO  NOT  need to be cut to
1/4 WL to provide an effective ground for a 1/4 WL vertical antenna WHEN
the raidials are ON the ground.

Does anyone know why a 1/4 WL vertical wire would indicate resonance
well ABOVE the expected frequency when fed against a single ground rod
in wet marshy clay type soil?

de   Tom   N4KG

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