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February 23rd 04, 10:04 PM

On Mon, 23 Feb 2004 13:43:55 -0600 (CST),
(Richard Harrison) wrote:

Dan Richardson wrote:
"The fact is resonance or not is not the determining factor."

Resonance of the antenna system is the determining factor in the
performance of a standing-wave antenna.

This is an amateur group, so you may check the "ARRL Antenna Book". My
19th edition has resonant antennas on page 9-2.

Fig 2 is a series RLC circuit representation of the typical
standing-wave antenna.

Ohm`s law should be noncontroversial (I=E/Z).
To maximize I with a given voltage, Z must be minimized. Z in the series
circuit is the phasor sum of R and X.

R has probably been established firmly in an antenna by its construction
and placement but we can tune the antenna system to make it resonant so
that we eliminate X to get maximum current into the antenna and to
thereby get maximum performance out of the antenna.

Best regards, Richard Harrison, KB5WZI

Hi All,

As a test of modeling and actual, real data, I put this to the test:

1.) I established two full quarter wave antennas;
2.) each with a set of 48 radials;
3.) tuned to 1.7 MHz;
4.) separated them by 20KM (100 wavelengths);
5.) set one to have a source of 1000W;
6.) loaded the other at the base with a 50Ohm resistor;
all in EZNEC with enough segments to hit the 500 limit.

When I called for the load data, EZNEC calculated it to be:
Power = 0.0008166 watts

This was by virtue of the receive antenna's length of 41.79M applying
the power across the resistor. In the standard of field measurement,
this reduced to
EÂ² = Power Â· 50Ohms
or
E = 202.1mV
or
4.84 mV/M

Now, for the reality check:

When I compare to the FCC Ground Wave charts for
1.) the same frequency;
2.) at 20KM distance;
3.) per 1KW of power
I found their forecast of
5 mV/M (within the accuracy of chart reading)

THEN, I reduced the same receive antenna's length to 1/10th Wavelength
and observed its load's response to the identical field:

Power = 7.804E-06 watts

This was by virtue of the receive antenna's length of 17.64M applying
the power across the resistor. In the standard of field measurement,
this reduced to
EÂ² = Power Â· 50Ohms
or
E = 19.8mV
or
1.12 mV/M
WHICH IS KNOWN TO BE FALSE!

The antenna, by virtue of its being shortened exhibits a reactance
-153.73 deg.

Being lazy, I monkeyed around with inductance values (aka tuning).
When I arrived on an Xl of 225Ohms the voltage across the resistor
showed:
E = 88.7mV
or
5 mV/M
WHICH IS KNOWN TO BE TRUE!

I also omitted pushing this inductor up into the antenna given this
exercise is oriented towards the SWLer who would not have that option
across the many frequencies offered.

This offers
1.) the commonplace observation of the transfer of power;
2.) the commonplace observation of the benefits of tuning;
3.) the validity of modeling confirmed through the commonplace
evidence of practice.

73's
Richard Clark, KB7QHC

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