Art Unwin, KB9MZ wrote:
"If you place some circuit close to a normal dipole the circuit will
take some of the energy from the dipole via coupling such that the
circuit will oscillate and reradiate at its resonant frequency or at a
frequency determined by its particular coefficient of coupling."

Not exactly.. To obtain continuous oscillation requires a gain equal to
loss in a circuit and introduction from the output to the input of the
circuit a sufficient fraction in the proper phase to reinforce signals
in the circuit.

An oscillator is likely to have its frequency affected by any external
coupling. That`s a reason to shield an oscillator and to provide a
buffer between its output and external circuitry.

A characteristic of a radio wave is its amplitude and frequency lock to
the generator which produces it. Subsequent mistreatment of the wave by
its environment is usually incapable of altering its alternations.

Best regards, Richard Harrison, KB5WZI

On Thu, 9 Oct 2003 21:14:08 -0500 (CDT),
(Richard Harrison) wrote:

Art Unwin, KB9MZ wrote:
"If you place some circuit close to a normal dipole the circuit will
take some of the energy from the dipole via coupling such that the
circuit will oscillate and reradiate at its resonant frequency or at a
frequency determined by its particular coefficient of coupling."


Hi Richard,

Obviously a case of not being able to distinguish between the usage of
oscillation and resonation.

73's
Richard Clark, KB7QHC

(Richard Harrison) wrote in message ...
Art Unwin, KB9MZ wrote:
"If you place some circuit close to a normal dipole the circuit will
take some of the energy from the dipole via coupling such that the
circuit will oscillate and reradiate at its resonant frequency or at a
frequency determined by its particular coefficient of coupling."

Not exactly.. To obtain continuous oscillation requires a gain equal to
loss in a circuit and introduction from the output to the input of the
circuit a sufficient fraction in the proper phase to reinforce signals
in the circuit.

An oscillator is likely to have its frequency affected by any external
coupling. That`s a reason to shield an oscillator and to provide a
buffer between its output and external circuitry.

A characteristic of a radio wave is its amplitude and frequency lock to
the generator which produces it. Subsequent mistreatment of the wave by
its environment is usually incapable of altering its alternations.

Best regards, Richard Harrison, KB5WZI

Richard,
If I have a loop circuit unconnected to a transmitter
could it not oscillate under ideal conditions?
If it can then would it not radiate at the frequency
that it is resonant at as well as reradiate at the
frequency of the energy input
Regards
Art

Art Unwin KB9MZ wrote:
If I have a loop circuit unconnected to a transmitter
could it not oscillate under ideal conditions?

Art, what is the power source?
--
73, Cecil, W5DXP

On 10 Oct 2003 08:06:45 -0700, (Art Unwin KB9MZ)
wrote:
Richard,
If I have a loop circuit unconnected to a transmitter
could it not oscillate under ideal conditions?
If it can then would it not radiate at the frequency
that it is resonant at as well as reradiate at the
frequency of the energy input
Regards
Art


Hi Art,

Distinguish between what resonates and what oscillates. Passive
circuits do not oscillate even though they support the flow of
alternating current. The ideal conditions for oscillation is the
presence of a power source, gain, and feedback. If any of the three
is missing, then there is no oscillation. The ideal conditions for
resonance is an external source of alternating current coupled to a
system that is harmonically related. If that system has no harmonic
relation, then there is no oscillation or resonation.

ALL systems that support the flow of alternating current radiate. How
well this is performed is called efficiency.

You cannot change a frequency without a nonlinear interface (like a
diode) or without the original excitation source containing spurs
(illegal at the antenna).

73's
Richard Clark, KB7QHC

Locate a tuning fork. Mount it any way you please. Then check it from
time to time to see if it spontaneously begins a sustained ringing.

As a mechanical engineer, you're well acquainted with the differential
equations that describe the motion of a physical object that's been
struck, for example a tuning fork. And you'll recall that the form of
the solution is a decaying sinusoid. An antenna or other resonant
circuit obeys the same equations and behaves the same way. In electrical
parlance, this response to excitation is called "ringing", after the
obvious physical equivalent. While a tuning fork or an antenna will ring
if excited, an antenna won't spontaneously ring, or produce a sustained
oscillation without an external source of power -- for exactly the same
reasons a tuning fork won't.

Roy Lewallen, W7EL

Art Unwin KB9MZ wrote:

Richard,
If I have a loop circuit unconnected to a transmitter
could it not oscillate under ideal conditions?
If it can then would it not radiate at the frequency
that it is resonant at as well as reradiate at the
frequency of the energy input
Regards
Art

Art Unwin, KB9MZ wrote:
"If I have a loop circuit unconnected to a transmitter could it not
oscillate under ideal conditions?"

Ideal conditions would require a source of energy to replenish losses in
the loop circuit. The source has to be the same frequency as that
consumed in operation of the loop.

A loop like any conductor or circuit has a self-resonant frequency. At
resonance, the conductor`s inductive and capacitive reactances cancel.
This zero reactance leaves only resistance to limit current in the
conductor. Some of the total resistance may be a coupled load, and some
will be radiation resistance, which is the conductor`s loss of r-f
energy to radiation. Some energy will be lost in conversion to heat at
the surface of the conductor and perhaps other locations.

At frequencies not too far from resonance, reactance of the wire rises
so high that little current flows and the wire has little effect on
anything.

Broadcasters are faced with structures which arise near their antenna
arrays. At times these are resonant at the broadcast frequency and if so
they absorb and re-radiate energy distorting the station`s radiation
pattern. The solution is usually simply applying something to the new
structure to detune it from resonance at the broadcast frequency. If not
very near resonance, the structure won`t pickup enough energy to cause
trouble. Too much reactance to allow current flow.

The hard fact that a structure must be near resonance to admit
significant energy makes broadbanding an antenna by an appurtenance
tuned to some frequency other than the fundamental frequency of the
antenna challenging. One method that works is a combination of antennas
resonant for all the desired frequencies.

There are other methods to get a wire to accept current over a wide
frequency range. Wave antennas are an example. But, standing wave
antennas are the most common and these need resonance or thereabouts.

Best regards, Richard Harrison, KB5WZI

Cecil Moore wrote in message ...
Art Unwin KB9MZ wrote:
If I have a loop circuit unconnected to a transmitter
could it not oscillate under ideal conditions?

Art, what is the power source?

Wow, this brought forth a lot of comments to contemplate.

Regarding your question. I was thinking of energy radiated
by a nearby source such as another radiator with very loose
coupling from which it gets energy, and current flows in the loop,
I then reason that with energy being applied to the loop it will also
create oscillation PLUS a emf feedback to the initiating energy
scource
which then also reacts giving a 'pulse' to continue oscillation as
well as energy for radiation. I see the loop not only reradiating the
initial frequency impinged upon it by the outside source but also a
radiation at the frequency of oscillation somewhat similar to that
seen in a receiver where the object is to bring the two frequencies
together. Now I am not electrically based and I am also guilty of
using wrong terms in my description but I am using the hobby
to experiment and learn. Now I did play with such a set up and was
able to see two frequencies on the 141T, Whether I interpreted
correctly what I saw is another matter. Fortunately I am not teaching
the subject or trying to make a living from it nor do I have a resume
to protect which gives me the opportunity to speculate, play around
with the hobby without the danger of being beheaded.
That is what is great about this hobby, it accepts all, the curious
and the appliance operators all of which are not frightened by showing
their ignorance of the subject but trying just the same. If I thought
I knew a bit about conjugate matches I would have participated in the
other postings but that was really beyond my ken and interest so you
lucked out there.
Cheers
Art

Richard Clark wrote in message . ..
On 10 Oct 2003 08:06:45 -0700, (Art Unwin KB9MZ)
wrote:
Richard,
If I have a loop circuit unconnected to a transmitter
could it not oscillate under ideal conditions?
If it can then would it not radiate at the frequency
that it is resonant at as well as reradiate at the
frequency of the energy input
Regards
Art


Hi Art,

Distinguish between what resonates and what oscillates. Passive
circuits do not oscillate even though they support the flow of
alternating current.

If what you state above is correct then I am wrong since basically
what I am descibing is a passive feedback circuitu

Art



The ideal conditions for oscillation is the
presence of a power source, gain, and feedback. If any of the three
is missing, then there is no oscillation. The ideal conditions for
resonance is an external source of alternating current coupled to a
system that is harmonically related. If that system has no harmonic
relation, then there is no oscillation or resonation.

ALL systems that support the flow of alternating current radiate. How
well this is performed is called efficiency.

You cannot change a frequency without a nonlinear interface (like a
diode) or without the original excitation source containing spurs
(illegal at the antenna).

73's
Richard Clark, KB7QHC

On 10 Oct 2003 20:01:49 -0700, (Art Unwin KB9MZ)
wrote:

Hi Art,

Distinguish between what resonates and what oscillates. Passive
circuits do not oscillate even though they support the flow of
alternating current.

If what you state above is correct then I am wrong since basically
what I am descibing is a passive feedback circuitu

Art

Hi Art,

There is no such thing as "passive feedback." Feedback is a property
of active circuit design to serve the purpose of tailoring input and
output characteristics.

You simply have to accept the conventional terms instead of making
your own up. What you describe, and has been pointed out to you by
others here recently is simple "coupling." This is not to say
coupling is simple - well, it is, but in the classic sense of being
fundamental. Coupling can be used to affect input and output
characteristics, as you inappropriately label as "passive feedback,"
but you really need to get a grounding in the fundamentals of this
action. This, of course, leads to the study of fields, and as you may
well appreciate that this is no simple course of study either.

73's
Richard Clark, KB7QHC