I would like to know the input resistance, at resonance, of a
1/4-wavelength counterpoise, at a low height above a ground of known
conductivity.

It will require modelling on an NEC-type program which takes soil
conductivity and very low heights accurately into account. If there
is such a program!.

The counterpoise can be modelled as a low-height, Inverted-L antenna
with the vertical and horizontal sections totalling 1/4-wavelength.

Modelled at approximately -

2 MHz and 10 MHz.

With heights above ground approximately -

0.005, 0.1, 1.0 metres.

With wire diameter = 1.6 mm or 14 awg.

With ground resistivities -

50, 200, 1000 ohm-metres.
(20, 5, 1 milli-Siemens).

I am interested only in input resistance. Input reactance will be
small when near resonance. Input resistance will not change very much
in the vicinity of resonance. So obtaining exact resonance is not
necessary. I would be happy with resistance values accurate to within
15 or 20 percent.

If anyone has a suitable modelling program and the time to spare I
would be very grateful. Just one or two figures would be useful.
----
Reg, G4FGQ.

Reg Edwards wrote:

I would like to know the input resistance, at resonance, of a
1/4-wavelength counterpoise, at a low height above a ground of known
conductivity.

A physical 1/4 wavelength (234/f) counterpoise is not
resonant at low heights so you must be talking about
an electrical 1/4 wavelength? For a fixed length, the
resonant frequency will change with height.

Can EZNEC be used for some of the configurations?
For instance, given my ground description (0.005, 13)
set for EZNEC, a 62 foot dipole one foot above ground
has a feedpoint impedance of 97 ohms on 7.188 MHz. Would
that imply a radial impedance of 48.5 ohms? The same
dipole 0.1 foot above ground shows an impedance of
112 at 5.94 MHz.

It seems as the wire gets closer to ground, the feedpoint
virtual impedance increases because the forward and
reflected waves on the radial are attenuated by the
ground. This rise in impedance is sometimes separated
out as "ground-loss resistance".

Roy, can NEC4 be used to model an underground dipole?
--
73, Cecil http://www.qsl.net/w5dxp

On Wed, 25 Jan 2006 15:01:45 +0000 (UTC), "Reg Edwards"
wrote:

I would like to know the input resistance

C'Mon Punchinello,

((( ***** for other readers, spoiler follows ***** )))

Yet another troll. This is another facile introduction to how you
would do it yourself to prove all the nodding heads wrong.

Then you will rummage up an unzipped program and offer it as the last
word.

Then you will sneer at software users as troglodytes who cannot rub
two brain cells together to derive Lord Plushbottom's principles of
transmission loss off a cable being draped across the bottom of the
Atlantic.

Of course, I will leave you with the last 27 or 13 posts in rebuttal
as this will play out to its obvious conclusion.

73's
Richard Clark, KB7QHC

that's a bit mean, Reg is trying to help radio enthusiasts with his hard
work, and mathematical problem solving skills, he is a good man to have in
your tool box!
Some of us appreciate his hard work.

On Thu, 26 Jan 2006 00:39:38 GMT, wrote:

that's a bit mean, Reg is trying to help radio enthusiasts with his hard
work, and mathematical problem solving skills, he is a good man to have in
your tool box!
Some of us appreciate his hard work.

If you were a troglodyte that suffered his lamentations (is your IQ
higher than the orphans of Brazil, AKA the sewer rats of Rio?) you
might feel different. A touching commendation nonetheless, but
Punchinello can go 120 rounds without a Jerry Lewis telethon. You
give him far too little credit.

Perhaps if you
1. signed your gift card;
2. offered an example;
then this would make it by air mail.

73's
Richard Clark, KB7QHC