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VK3ABK > ANTENA 06.01.05 14:34l 67 Lines 2851 Bytes #999 (0) @ WW
BID : 34929_VK3KAY
Read: GUEST DG8DG DL5DKW OK1VKZ
Subj: Antennas and why? Again.
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<DK0WUE<7M3TJZ<HG8LXL<KP4IG<W1NGL<VK6HGR<
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Sent: 050106/1201Z @:VK3KAY.#WEV.VIC.AUS.OC #:34929 [Wendouree] $:34929_VK3KAY
From: VK3ABK@VK3KAY.#WEV.VIC.AUS.OC
To : ANTENA@WW
Hello all Impedances!
I thought, when I sent a bulletin about antennas it would raise a bit of
interest on packet, but apart from Rudolf, PF1F, there has been no response.
Rudolf started his comment with a question of his own. A question that has
been troubling novices who have been taught plumbing and water works!
Rudolf wrote...
"....and it is the very reason that mains sockets have holes that close when
it is not in use (except outside England)."
Those mains sockets should be sold with buckets attached!
"This prevents the 0.64 Amperes flowing into free space otherwise.
We can't have all those amps sloshing about the floor!"
This would cause much plugging of holes in the Dykes in PE/PF land.
But then he gets serious. (I think)
"There is no more reason for the terminal impedance of an antenna to equal
the impedance of free space than there is for the terminal impedance of a
loudspeaker to equal the acoustic impedance of free air - or even to have
some relation to it."
Sorry, But I don't agree that this is a valid comparison. You might as well
say that the RF amplifier rating is important to the type of antenna.
But to apply Rudolf's audio analogy further, I believe that the acoustics of
a system can be likened to an RF transmission. In dealing with a mass of
air, say in airconditioning, or the exhaust of a car or motorcycle, it is
most important to 'match' the 'transmission line' and provide a compatible
'load' for best air flow, noise reduction, and performance of an engine.
And again...
"That efficiency is difficult to attain with low radiation resistance, is
quite another matter."
I also agree, but think 'efficiency' is at the heart of the matter.
However, thinking further about the 'space field' and coupling an antenna to
'free space' you will soon arrive at Poynting Vectors and the power in the
H and E components using P = H x E where P is in Watt per metre squared.
( I have trouble showing this vector notation in heavy type, even though I
hit the keys pretty hard :-). It works with my old Remington typewriter! )
In considering 'power' in a transmission wave, we soon come to impedances,
matched or otherwise.
The H and E fields form a 'structure' to enable our RF energy to be radiated
through 'empty' (?) space. To me, this can be compared with the gravitational
field (also permeating free space) that we know exists but remains a mystery.
I wonder if there is a connection?
But this is getting away from the original points I was making, that is how
does the antenna 'launch' a wave into space to begin with. An antenna should
present the best interface with the outside world so that our radios are
'effective', and as 'efficient' as possible.
Come on! Rudolf seems to be the only one who has something to say.
73. Dick. VK3ABK.
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