On Mon, 14 Jul 2003 22:01:59 +0000 (UTC), "Reg Edwards"
wrote:

Actually, when the transmitter circuitry folds back, it means that the
antenna system is not resonant.
==================================

Wrong ! The antenna 'System' IS resonant, by definition, if it has a purely
resistive input impedance. If that interfering nuisance of your fold-back
circuit springs into action then it means the pure input resistance is
something other than 50 ohms. But it is still resonant.

Actually, in YOUR case, the antenna is NEVER resonant. You make sure the
antenna is NOT resonant by making the whole system resonant by varying the
length of your transmission line.
---

Hi Troll,
let's talk about measuring antenna impedance.

I have got a MFJ 269 which clearly shows that none
of my antennas is purely resistive, or resonant.


w.

Reg wrote,

Richard, thanks for the reminder.

Yes, the Beverage and other long-wire terminated antennas, although having
lots of L and C, exhibit (ideally) no signs of resonance yet have purely
constant vs frequency resistive feedpoint impedances.

They are all transmission lines which radiate because the spacing between
conductors is an appreciable fraction, or more, of a wavelength, one of the
conductors being whatever the local environment consists of.

Their equivalent lumped circuit networks come under a class of
'constant-resistance' networks commonly found in design of filters and
equalisers.

The most simple example of a constant-resistance network is a capacitor in
series with a resistor, both in parallel with an inductor in series with a
resistor. When all 4 components have the same value in ohms (R) then the
input resistance is a constant resistance R from DC to infinity.
----
Reg, G4FGQ


Since the reactive components change reactance with frequency, Reg's network
may be a little hard to realize in practice. Try making the inductance equal
to
R^2*C Reg. You might have better luck. You also might want to review
Everitt's
take on this subject, starting on page 284 of the second edition of his book,
_Communication Engineering_. His ideas are quite enlightening.

73,
Tom Donaly, KA6RUH

The most simple example of a constant-resistance network is a capacitor
in
series with a resistor, both in parallel with an inductor in series with
a
resistor. When all 4 components have the same value in ohms (R) then the
input resistance is a constant resistance R from DC to infinity.
----
Reg, G4FGQ


Since the reactive components change reactance with frequency, Reg's
network
may be a little hard to realize in practice. Try making the inductance
equal
to
R^2*C Reg. You might have better luck. You also might want to review
Everitt's
take on this subject, starting on page 284 of the second edition of his
book,
_Communication Engineering_. His ideas are quite enlightening.

73,
Tom Donaly, KA6RUH

=========================================

Tom, sorry to be so disappointing. My Little formula for calculating L and
C for the constant resistance network is quite correct.

When designing constant-resistance networks it is convenient to have a
design-frequency.

It can be the frequency at which I said Xc = Xl = R ohms.

So we can now calculate both L and C without prior knowledge of either of
them. After a little arithmetic it will be quite enlightening to discover ,
as you say, that L = C*R^2, but which is a less-convenient starting point.

In addition to a design frequency there can also be a design time constant.
---
Reg, G4FGQ

Reg wrote,

Tom, sorry to be so disappointing. My Little formula for calculating L and
C for the constant resistance network is quite correct.

Yes, of course, but misleading because it implies that all four components
have to have the "same value in ohms (R)." In fact, the input resistance will
be the same no matter what the value of the reactive components as long as
they obey the requirement that L/C = R^2.


When designing constant-resistance networks it is convenient to have a
design-frequency.

Convenient, but not necessary to show that constant resistance networks exist.



It can be the frequency at which I said Xc = Xl = R ohms.

It can, indeed, or any other frequency for that matter.


So we can now calculate both L and C without prior knowledge of either of
them. After a little arithmetic it will be quite enlightening to discover ,
as you say, that L = C*R^2, but which is a less-convenient starting point.

Perfectly true, but what are you ultimately after?


In addition to a design frequency there can also be a design time constant.

Indeed.

---
Reg, G4FGQ


Tom Donaly, KA6RUH

Perfectly true, but what are you ultimately after?

=======================

Beyond getting back to the subject matter - nothing!

Jack, K9CUN wrote:
"I have referred to my various engineering texts on antennas and
transmission lines and can not find any discussion of antenna "vigor"."

I did not copy my statement. Vigor is defined in my "American College
Dictionary as: "1. active strength or force---".

A rod in free space becomes excited and accepts energy, which it must
re-radiate, when it is swept by a passing wave of its resonant
frequency. Its first resonance is near a 1/2-wavelength. At frequencies
slightly off-resonance, little current flows in the rod due to the
opposition of its reactance.

You may have seen a mechanical analogy in the vibrating reed frequency
meter.

Best regards, Richard Harrison, KB5WZI

Is that as in: "Oomph, oomph, omphpapa"? Oh! My poor tuba!!

Deacon Dave :-), W1MCE

Roy Lewallen wrote:
The correct technical term for this is "oomph".

Roy Lewallen, W7EL

JDer8745 wrote:

Someone sed:

"I wrote that if the antenna is operated off-resonance (excited by a
frequency other than its resonant frequency) it works but with less
vigor etc."

------------------------------------

I have referred to my various engineering texts on antennas ans
transmission
lines and can not find any discussion of antenna "vigor".
Jack K9CUN

I have referred to my various engineering texts on antennas ans transmission
lines and can not find any discussion of antenna "vigor".

Jack K9CUN



It is Viagora, it makes all antennas resonanted and transmission lines SWRless.
Add some Fractals, CFAs, EH?

Bada BUm

Vigor is defined in my "American College
Dictionary as: "1. active strength or force---"

--------------------

What is the "strength" of an antenna?

What is the "force" of an antenna?

Is it the same as the "oomph"?

73 de Jack, K9CUN

On 18 Jul 2003 18:42:00 GMT, (JDer8745) wrote:

Vigor is defined in my "American College
Dictionary as: "1. active strength or force---"

--------------------

What is the "strength" of an antenna?

What is the "force" of an antenna?

Is it the same as the "oomph"?

73 de Jack, K9CUN

Hi Jack,

Strength is often associated with potential (Volts being common here).

Force is more often associated with power (by virtue of Newton, Watts
being common here).

oomph is what an old fart mutters as he stirs uncomfortably in his
chair while avoiding a bench test of his mental gymnastics.

73's
Richard Clark, KB7QHC