The earth
In message , NM5K writes
On 4/16/2012 3:40 AM, Szczepan Bialek wrote:
"Is the original claim wrong?S*
Let me try this again in a repeating manner you might possibly be
able to understand. I'm surely not going to hold my breath waiting for
viable indications of comprehension, but here goes..
Yes.
Yes, the man was wrong!
But he had an excuse.. It was 1909.
Good grief... It does boggle the mind.. :|
In the early days of radio, most experimenters tended to think of
antennas as working by RF alternating currents charging (and
discharging) a big capacitor in the sky via a long, vertical wire (or
multiple wires, to increase the capacity, and to minimise losses).
To push and pull the current in and out of the capacitor, it was
necessary to have a good, solid, zero-potential reference point, and the
best one available was ground/earth (or, at sea, the hull of the ship).
So, for the types of antennas being experimented with (and used) at the
time, Marconi was absolutely correct.
Also, it wouldn't have taken them long to appreciate the benefits of
bringing the antenna system to resonance on the frequency the operators
wanted (rather than it simply being an act-of-God and hope-for-the-best
affair).
But note that with Marconi's famous crossing the Atlantic experiment, I
believe there is no documentation of exactly what frequency was used.
Instead of it being something extremely low (which is what they
expected), it is now thought that the signal which travelled 3000 miles
would have been one of the many harmonic resonances of the antenna, as
this would have been excited by the extremely wide band of frequencies
created by the spark transmitter. Knowing now what frequencies cross the
Atlantic in daylight, the signal might have been as high as 10 or 15MHz
(frequencies which Marconi only dreamt about using!).
--
Ian
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