Howdy,

What's all this stuff about resonant antennas? Some great antenna designs do
not use a resonant length.

73 de Jack, K9CUN

What's all this stuff about resonant antennas? Some great antenna designs
do
not use a resonant length.


All antenna 'systems' are resonant because they all present a resistive load
to the transmitter. QED.

Reg Edwards wrote:
All antenna 'systems' are resonant because they all present a resistive load
to the transmitter. QED.

Actually, when the transmitter circuitry folds back, it means that the
antenna system is not resonant. When I change bands with my screwdriver
and start tuning, my antenna system is certainly not resonant.
--
73, Cecil http://www.qsl.net/w5dxp
"One thing I have learned in a long life: that all our science, measured against
reality, is primitive and childlike ..." Albert Einstein



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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.
---
Reg,

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.

Reg, the chances of a foldback being caused by a resistive antenna is
about 1 in 360. Actually less than that because the transmitter will
not fold back between 25 ohms and 100 ohms.
--
73, Cecil http://www.qsl.net/w5dxp
"One thing I have learned in a long life: that all our science, measured against
reality, is primitive and childlike ..." Albert Einstein



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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.

Hi Reg,
That foldback circuit is an interfering nuisance agreed, but it comes in
handy at times. My homebrew mobile antenna is difficult to keep tuned, much
less in one piece doing 100 km/hr down the US Interstate system. My HF
transceiver folds back if things are not right with the antenna system.
The fold back circuits tell me I need to do something with the mobile
antenna, before I smoke the final semiconductors in my rig. It doesn't tell me
what I need to do, I use other stuff for that. I used a couple of your
programs in the design of this beast, Thanks!
73 Gary N4AST

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 Edwards" wrote in message ...
What's all this stuff about resonant antennas? Some great antenna designs
do
not use a resonant length.


All antenna 'systems' are resonant because they all present a resistive load
to the transmitter. QED.

I suppose I am being picky Reg but shouldn't resonance be defined as
"totally" resistive load. An antenna can only be 'resonant' at one
point or frequency because movement from this point collects
reactance.
Fortunately it still has a 'resistive' component load which is the
PRIME requisite for radiation, whereas 'resonance' is not.
With the above being fully understood by newcomers a lot of the
mystery about 'antennas' and 'antenna systems' falls aside.
Cheers
Art

What's all this stuff about resonant antennas? Some great antenna designs do
not use a resonant length.

73 de Jack, K9CUN

Hi Jack,
When you posed this same query back in June of 1999, (myth od the resonant
antenna) you got 193 responses. You trying to beat your own record?
That was about the time I happened upon this Newsgroup, I really enjoyed that
particular thread. I have gone back and re-read it a couple of times.
73 Gary N4AST

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