On Sun, 22 Feb 2004 13:07:46 -0600 (CST),
(Richard Harrison) wrote:

A receiving antenna must be resonant to enable full acceptance of
available energy,

Where did you come up with that one?

I suggest you revisit capture area.

Danny, K6MHE

Don, K6MHE wrote:
"Where did you come up with that one?"
(A response to my statement that a receiving antenna must be resonant to
enable full acceptance of available energy)

I`ve tweaked antenna trimmers which dramatically boosted the signal when
reasonance was reached. I`ve seen grounded 1/4-wave structures near a
broadcast station detuned, thus eliminating the distortion they had
caused in the station`s radiation pattern. If they`re not resonant, they
don`t accept enough energy to make any difference in the station`s
pattern.

!/2-wave wires in free-space are resonant. Resonance is defined as unity
power factor, that is, XL=XC. At resonance, reactance is balanced out
and only resistance is left to oppose current in a wire. Usually the
wire has a radiation resistance which is large as compared with its loss
resistance in practical antennas.

At frequencies below first resonance, the ungrounded wire is less than a
1/2-wavelencth. It has a low radiation resistance and a high capacitive
reactance. We can add inductance to tune the wire to resonance.

At frequencies above first resonance, the ungrounded wire is more than a
1/2-wavelength, and if it is not much longer, the wiire has an inductive
reactance. The phase flip-flop at resonance is abrupt and the reactance
is an impediment to the current on either side of resonance. The correct
series capacitor can be placed in series with the roo-long wire to tune
out its excess inductive reactance.

A mechanical analog is the vibrating-reed frequency meter used at power
frequencies. All the reeds are in the power-frequency field. Only the
reed of resonant length has so little opposition to the excitation that
it vibrates freely.

A versatile antenna tuner can insert either inductive or capacitive
reactance in series with an antenna to correct its power factor (tune it
to resonance) so it can accept maximum excitation.

Best regards, Richard Harrison, KB5WZI

On Mon, 23 Feb 2004 08:54:50 -0600 (CST),
(Richard Harrison) wrote:

A versatile antenna tuner can insert either inductive or capacitive
reactance in series with an antenna to correct its power factor (tune it
to resonance) so it can accept maximum excitation.

I believe you are confusing matching with antenna operation (gain and
efficiency). Using a simple dipole for example, you can calculate both
gain and efficiency using NEC. Doing that I have modeled a dipole at
3/8, 1/2 and 5/8-wavelengths (80-meter band). The antenna was modeled
using #14 copper wire in free space. Here is what NEC reported:

Wavelength Gain(DBi) Efficiency

3/8 1.8 96.36%
1/2 (resonate) 2.02 97.22%
5/8 2.29 97.72%

Clearly you should be able to see that only advantage is that the
longer antenna has greater the gain and efficiency. The fact antenna
is resonance or not is not the determining factor.

73
Danny, K6MHE

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

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
E² = Power · 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
E² = Power · 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

Let me try this one more time. You had posted earlier and I commented
on this:

"A receiving antenna must be resonant to enable full acceptance of
available energy, and it must be matched to avoid re-radiation of more
than 50% of the energy it is able to grab."

I commented on the first portion of your statement (above). My only
point is that it makes no difference if an antenna's is resonate or
not in determining how much energy it grabs.

That's it, nothing more.

73
Danny, K6MHE


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

Dan it is wise to remember that Richard "cherry picks" statements from
assorted books and disregards the chapter heading and what is discussed in
that chapter. He only looks for a statement that suits his present state of
mind and suggests authority and ignores the underlying subject of the
thread. In that same chapter it is discussed how the losses mount up as you
move away from the resonant point and shows where the losses could amount to
5dB no less. There is a proviso
in that the antenna books that I have precede the one that he is refering to
so there may be some evidence that somebody has pushed the envelope beyond
Maxwell and others.
I think the actual chapter refers to broadband antennas rather than those of
a narrow bandwidth so it is always advisably to check so called "book
quotes" rather than accept what people interprete what is relavent in their
own minds.
Regards
Art


"Dan Richardson @mendolink.com" ChangeThisToCallSign wrote in message
...
Let me try this one more time. You had posted earlier and I commented
on this:

"A receiving antenna must be resonant to enable full acceptance of
available energy, and it must be matched to avoid re-radiation of more
than 50% of the energy it is able to grab."

I commented on the first portion of your statement (above). My only
point is that it makes no difference if an antenna's is resonate or
not in determining how much energy it grabs.

That's it, nothing more.

73
Danny, K6MHE


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

Art, KB9MZ wrote:
"Dan it is wise to remember that Richard "cherry picks" statements from
assorted books and disregards the chapter heading and what is discussed
in the chapter."

Forget the books! Surely some time in your long career you`ve peaked an
antenna trimmer and it worked. Why?

Best regards, Richard Harrison, KB5WZI

Dan, K6MHE wrote:
"My only point is that it makes no difference if an antenna`s is
resonate or not in determining how much energy it grabs."

Not in the "grand scheme of things", perhaps, but a resonant antenna
extracts more energy when swept by a traveling wave than an
off-resonance conductor does at the same distance from the transmitter.

On some occasion you may have adjusted the antenna trimmer on a receiver
and found a signal peak. That adjustment balanced out the reactance in
the antenna system leaving only the antenna resistance to oppose current
flow in the antenna. Proper adjustment maximizes antenna current induced
by the wave.

The mechanism is simple. The antenna is a series RLC circuit. Current in
the antenna is a function of the field strength divided by the impedance
of the RLC circuit. Impedance to antenna current is least when all of
the reactance has been eliminated. You have probably experienced peaking
the signal this way with your ears, a meter, or an oscilloscope.

Let`s look at an oft repeated type of true story by John E. Cunningham
in his "Complete Broadcast Antenna Handbook":

"Not every tall structure will affect the pattern of a broadcast
station. The effect on the pattern depends on the height of the
structure. In one case, a microwave tower was erected, one section at a
time, near a 4-tower directional antenna system. As construction
progressed, the current in one tower began to drop as each new tower
section was added to the microwave tower. The current continued to drop
until it nearly reached zero. But, as more sections were added to the
microwave tower, the current began to rise. When the microwave tower
reached its final height, all of the tower currents of the broadcast
antenna, as well as the pattern, were normal.

Resonance, or lack of resonance, makes all the difference!

Best regards, Richard Harrison, KB5WZI

On Mon, 23 Feb 2004 17:47:15 -0600 (CST),
(Richard Harrison) wrote:

Not in the "grand scheme of things", perhaps, but a resonant antenna
extracts more energy when swept by a traveling wave than an
off-resonance conductor does at the same distance from the transmitter.

So according to you, as an example, a resonate 1/4 or 1/2 monopole
will extract more energy than a non-resonate 5/8-wave monopole.

Enjoy your dreams, I'm QRT

73
Danny, K6MHE