Units of force do not include Watts.

Units of force are such things as Newtons, dynes, poundals, pounds, etc.

Jack (who exerts a force of many pounds on this chair)

73

Reg, G4FGQ wrote:
"All antenna "systems" are resonant because they present a resistive
load to the transmitter. QED."

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

But...is an antenna "system" (undefined) the same as an antenna?

Methinks an antenna is just one part of an antenna "system" and that it doesn't
need to be resonant.

73 de Jack, K9CUN

JDer8745 wrote:

Reg, G4FGQ wrote:
"All antenna "systems" are resonant because they present a resistive
load to the transmitter. QED."

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

But...is an antenna "system" (undefined) the same as an antenna?

[SNIP] NOPE!!


Methinks an antenna is just one part of an antenna "system" and that it doesn't
need to be resonant.

73 de Jack, K9CUN

Methinks an antenna is just one part of an antenna "system" and that it
doesn't
need to be resonant.

and you are basically correct. an antenna is 'resonant' at only specific
frequencies, even a small bit away from those frequencies it goes out of
resonance but performance is virtually unchanged... if this weren't true the
venerable 1/2 wave dipole and 1/4 wave verticals would only work on a single
frequency... so we know from experience that you don't have to have an
exactly resonant antenna.

note above i said 'frequencies'. this is to account of course for the
resonances at multiples of the lowest resonant frequency.

likewise you can operate an antenna well away from it's resonances and it
will still 'work'... theoretically an infinitely small dipole will radiate a
field only a couple db weaker than a 1/2 wave dipole in free space... with
the difference being that the 1/2 wave dipole changes the shape of the
doughnut a bit, thus creating stronger fields in some directions and weaker
ones in other directions. keep raising the frequency so that an antenna is
longer and longer as measured in wavelengths and the pattern of these fields
changes, but the total radiated power remains the same... so you can say
that any antenna 'works' at any frequency and be correct.

The kicker comes when you start considering the whole system. while any
antenna will radiate whatever power you get into it (minus a bit for
resistance of the elements that gets lost as heat), the problem can be
getting that power to go into it in the first place. this is where the
'resonant' antenna does help out. at resonance an antenna presents a purely
resistive impedance to the feed line, generally this is a relatively easy
load to push power into.... except of course in extreme cases of very low or
very high impedances. as such it simplifies the requirements for the
feedline and transmitter.

if a transmitter doesn't have to handle highly reactive loads, or extremely
high or low impedances, it can be made much simpler and from easier to build
or buy parts. if you have to design a transmitter to power a highly
reactive load you have to be able to handle higher voltages or currents...
higher voltages mean wider capacitor spacings, more insulation, and higher
dielectric losses.. higher currents mean thicker conductors or expensive
plating to lower resistance, and higher resistive losses.. both of those
losses mean that in order to create the same radiated field intensity you
need to generate more power in the transmitter to get it through the feed
system to the antenna where it can be radiate. so while the antenna will
radiate whatever you can give it, just getting it there in the first place
can be a chore.

"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

Yuri Blanarovich wrote:
Here is your answer Cecil. Resistor that radiates.

If, as Jim says, an RF wave is not destroyed by being dissipated
in a resistor dummy load, it has to radiate - yes? no?
--
73, Cecil http://www.qsl.net/w5dxp



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Reg Edwards wrote:
It is only necessary that the load presented to the transmitter should
be a
pure (or near enough) resistance of the required value. Which is usually
50
ohms.

My SGC-500 amp says it will handle an SWR of 6:1 just fine.
If that is true, it means it will handle any impedance on
or inside a 6:1 circle on a 50 ohm Smith Chart. The great
majority of those impedances are not resistive.
--
73, Cecil, W5DXP

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

Dear Talking SGC-500,

Why do think I took the precaution of qualifying my statement with "or near
enough" ?

By the way, you would be most unhappy if your Tuned-tank or Pi-tank output
circuit didn't present your plate(s) with a near-enough purely resistive
load of the correct value. And would you mind asking your slave driver to
stop cheating with the aid of his 19th Century Smith Chart, please.
----
Reg, G4FGQ

I was taught that the Smith CHart is a twentieth [20th] century 'tool'.

BTW, it's not cheating! When I took my final exam in transmission lines
Professor James Kirwin allowed, and even provided, Smith Charts for
student use.

DD, W1MCE

Reg Edwards wrote:
[SNIPPED]
...
And would you mind asking your slave driver to
stop cheating with the aid of his 19th Century Smith Chart, please.
----
Reg, G4FGQ

Oh Yuri!! All resistors in any circuit radiate EM energy!

DD, W1MCE

....and cause SWR. Can you picture little, unmatched radiating resistor in the
circuit? Live and learn eh?
I thought they ate the RF without passing any to our precious environment. What
me dummy!
But I think we should start new thread or threat on how much resistor,
capacitor or asamatteroffact anything radiates, how the SWR affects this
un/desired property, what the photons and black holes do about it and how to
magnify this effect so we can beat the record on number of postings.
Back to my no SWR feedlines.

Bada Fun BUm

Yuri Blanarovich wrote:
Oh Yuri!! All resistors in any circuit radiate EM energy!

...and cause SWR. Can you picture little, unmatched radiating resistor in the
circuit? Live and learn eh?
I thought they ate the RF without passing any to our precious environment.

They do eat RF without passing more than a negligible amount to our
environment. But they also convert the energy from RF energy to radiated
heat which is just as much of an EM wave as the RF wave was. The old
RF wave is destroyed but since the energy in that RF wave cannot be
destroyed, it must be converted. In this case it is converted to
an infrared wavelength.

The way to keep a resistor from radiating heat is to enclose it in
a heat sink in which case the heat sink probably radiates heat as
well as conducts heat.
--
73, Cecil http://www.qsl.net/w5dxp



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