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VK3ABK > TECH 22.05.07 05:33l 67 Lines 3870 Bytes #999 (0) @ WW
BID : 56904_VK3HEG
Read: GUEST OE7FMI
Subj: Antennas and EM waves. (HB9ABX)
Path: DB0FHN<DB0MRW<DK0WUE<CE8FGC<ON0BEL<VK7NW<VK3HEG
Sent: 070522/0421Z @:VK3HEG.#WEV.VIC.AUS.OC #:56904 [Ballarat] $:56904_VK3HEG
From: VK3ABK@VK3HEG.#WEV.VIC.AUS.OC
To : TECH@WW
Hello Antenna Sceptics.
This may be a good time to comment on some interesting bulletins from the
ever enterprising Felix, HB9ABX. A good time, as there is a lull in bulletins
of 'words and other contentious comment'. No problem there!
I have always read the bulletins from Felix with interest. He is sincere in
his experiments with antennas, and has always generated 'heated debate', for
want of a better and more accurate term. The latest trilogy that Felix has
sent have a common thread that has always intrigued me; this is the link
between our antennas and the propagation medium and how the link can be
possible. There is no doubt that it works; but just how can the energy
generated by a radio transmitter be set through space, air filled or vacuum,
to be recovered at a distance. 'Recovered' may not be the right word
(no 'off topic' discussion please) as the percentage of the original energy
sent is 'efficient-less' (which may be another off topic word) which is not
to deny the comments by Felix and his aim for a maximum 'bang for his buck.'
(another word fest!) One can hardly talk about efficiency when we may
generate 'Megawatts' to be received as 'Microwatts' by an unsuspecting client!
By the way, we all know that to get maximum power transfered, our source and
load should have the same resistance/impedance. But tell the power station
manager who generates say, 500 Megawatts, that half of that should be
dissipated in his generator and note his reaction! (Off-topics welcome)
In a bulletin dated May 05, 'Generation of EM waves' Felix wrote ".....
EM waves are generated by two different principles: either by cyclic
accelleration of charges or by cyclic changing of electric fields."
The evidence he cites, the equations of James Clerk Maxwell, certainly deal
with the fields associated with a cyclic (rotating) electromagnetic source.
This tells us that for a magnetic field generated by an alternating current,
there is an electric field that coincides at right-angles. I take this to
mean, also, that a point source can be thought of as a 'generator' of both
an electric and a magnetic field, as has been described as a Poynting Vector,
usually written as P = k * E * B. That is, a product of both E, the electric
component, and B, the magnetic coincidence. This is possibly the mythical
point source that we are told is our antenna gain reference. (No doubt about
it. Anything greater that nothing must be gainful!)
Now, the trick is to get this dynamic electromagnetic sprite to combine with
sympathetic conveyance in space to transport the energy, along with any
perceived 'intellegence', to a distant receiver. According to the law of
reciprocity, this works for recieving, and here is where "...(Faradays's law
of induction)..." to quote from Felix's bulletin, comes to the rescue.
Fortunately for us, 'free space' has the properties of Permittivity and
Permeability, which combine to give an 'impedance' that can be used as a kind
of 'load' to absorb the energy in our electromagnetic field, and by a
marvelous 'sharing', common in physics and chemistry, spread it around like a
global warming rumour!
Well, that is what I have thought out from what Felix has suggested, and from
his comments about a '...high voltage RF source. In this kind of antenna, the
length of the antenna becomes very short." I suspect he is thinking of his
pet subject, a 'Roomcap Antenna'! And I suspect he is right, but it seems to
me that to get the maximum coupling to the 'impedance' of 'free space', which
is both and electric 'and magentic', we should expose as much of our energy
source as possible with a large/long antenna. This may be intuitive, but it
seems experimentally so.
Sent with degree of uncertainty; I haven't checked with the Internet sources
Felix has quoted.
73. Dick. VK3ABK.
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