W5DXP wrote in message ...
Dr. Slick wrote:
The funny thing about this, is that you cannot say that the 50
Ohms in the center of the chart is a "resistive" 50 Ohms, as there is
very little real resistance in the average antenna.

From the IEEE Dictionary: "resistance (1)(B) The real part of impedance."

Apparently, all the resistance in the average antenna is real. :-)
--


You misunderstand my point, Cecil.

If the antenna is tuned correctly, the "radiation" resistance is a
real 50 Ohms, with the V and I waveforms IN PHASE. But, my point is
that you can take a DC measurement anywhere on the ideal lossless
antenna and you will never see 50 Ohms anywhere, only shorts.

Ideally, the antenna never heats up, and has no resistive losses.
This is not to say that it won't have a "radiation" resistance of 50
Ohms at the resonant, tuned frequency. And to a transmitter at the
resonant frequency, this will electrically appear to be the same thing
as an ideal dummy load of 50 Ohms.

Roy's message has clarified a few things.


Slick

Dr. Slick wrote:

W5DXP wrote:
Apparently, all the resistance in the average antenna is real. :-)

You misunderstand my point, Cecil.

Actually, it was a play on words using your definition of "real" Vs
the IEEE Dictionary and mathematical definition of "real". The Devil
made me do it but I did provide a smiley face.
--
73, Cecil http://www.qsl.net/w5dxp



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Dr. Slick wrote:
"But, my point is that you can take a DC measurement anywhere on the
ideal lossless antenna and you will never see 50 Ohms anywhere, only
shorts."

True. D-C resistance of a lossless wire is zero. But, apply 50 watts r-f
power to an antenna adjusted to present 50-ohms resistance at a
particular frequency.

What happens? Our loading, adjusted for 50 watts output, produces 50
volts at an in-phase current of 50 amps.

The 50 watts is being radiated. As far as the transmitter is concerned,
the power might just as well be feeding a dummy load.

There are several reasons a d-c ohmmeter doesn`t read radiation
resistance. Once the ohmmeter`s d-c has charged the antenna, current
flow stops. D-C doesn`t radiate. A d-c ohmmeter doesn`t even measure the
right loss resistance value. Some of the loss resistance in a true
antenna with actual losses, comes from skin effect at radio frequencies,
where the conduction is forced to the outside of the conductors,
decreasing their effective cross-section and increasing their loss. R-F
also has the ability to induce eddy currents in surrounding conductors
and to agitate molecular movement in surrounding insulators. R-F thus
increases loss over that measured by passing d-c through the antenna.

Radiation resistance can be readily measured by using an r-f bridge
instrument. The bridge and antenna are excited by a generator operating
at the same frequency the transmitter will use. The bridge will indicate
reactance in the antenna, if it is not resonant. The null detector for
the bridge is typically a good radio receiver.

Radiation resistance is real though it does not heat the antenna. Loss
resistance is real though it does heat the antenna and its surroundings.

A resistance is a volt to amp ratio in which amps are in-phase with the
volts.

A resistor is a special type of resistance in which the electrical
energy applied to the resistance is converted into heat.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
What happens? Our loading, adjusted for 50 watts output, produces 50
volts at an in-phase current of 50 amps.

Hmmmm, 50 watts in, 2500 watts out. How much will you take for
that antenna, Richard? :-)
--
73, Cecil http://www.qsl.net/w5dxp



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I would like one of those antennas!!

BTW, it should be patented!! It looks better than some I've read about!!

;-)

DD, W1MCE

W5DXP wrote:

Richard Harrison wrote:

What happens? Our loading, adjusted for 50 watts output, produces 50
volts at an in-phase current of 50 amps.


Hmmmm, 50 watts in, 2500 watts out. How much will you take for
that antenna, Richard? :-)

(Richard Harrison) wrote in message ...
Dr. Slick wrote:
"But, my point is that you can take a DC measurement anywhere on the
ideal lossless antenna and you will never see 50 Ohms anywhere, only
shorts."

True. D-C resistance of a lossless wire is zero. But, apply 50 watts r-f
power to an antenna adjusted to present 50-ohms resistance at a
particular frequency.

What happens? Our loading, adjusted for 50 watts output, produces 50
volts at an in-phase current of 50 amps.



That would be 2500 watts? I assume you mean 50 volts and 1 amp to
get 50 watts.



Radiation resistance can be readily measured by using an r-f bridge
instrument. The bridge and antenna are excited by a generator operating
at the same frequency the transmitter will use. The bridge will indicate
reactance in the antenna, if it is not resonant. The null detector for
the bridge is typically a good radio receiver.

Radiation resistance is real though it does not heat the antenna. Loss
resistance is real though it does heat the antenna and its surroundings.

A resistance is a volt to amp ratio in which amps are in-phase with the
volts.


The key here is IN-PHASE. If you read my other post, you and Roy
have clarified this for me: Both radiation resistance and dissipative
resistance are the real portion of the impedance.


A resistor is a special type of resistance in which the electrical
energy applied to the resistance is converted into heat.


With very little radiated energy.


Thanks for the input,

Slick