Hi Rik,
I did a little test on saturday afternoon :
I did put the lower part of the loading coil (that is normally in
horizontal position) vertical (directly under the wire).
I did measure the antenna current and the signal strength of DCF39, in
both
cases not the slightest difference.
Interesting.
Some time ago, while operating from Amberley Museum, we had a Tesla coil
group giving a demonstration. It was though that this would cause
interference with my operation, located about 1km away. It did not.
Out of curiosity I took my mobile LF equipment and parked close (100m) to
where the Tesla group were demonstrating. I enquired as to what frequency
they were operating on. It seemed to depend on the size of the coil - small
coils and small sparks used higher frequencies, around 200kHz. The very big
coils operated on lower frequencies - around 70kHz - as you might expect.
I set up the LF receiver with a short length of wire so that I could hear
the stronger commercial stations. When the Tesla coils were fired up tuned
around and heard - nothing!
This surprised me. I expected, with that degree of power being used for the
receiver to be overwhelmed.
The Tesla coils were close wound with an annular metal capacity top from
where the sparks were induced with an earthed wand.
Now Toni, HB9ASB, used a coil as an antenna on LF, see page 58 of the LF
Experimenter's book. This type of coil is known as the Normal Mode Helix.
This type of antenna is incorporated into Rubber Duck antennas used with
VHF/UHF handhelds.
A mathematical analysis of this antenna is given, in the discussion of
different types of antennas, in Corum's torodial antenna patent application.
At the end of this analysis is the following:
"There is an alternative way to derive Equation 1. (from the analysis just
described), which proceeds from the introduction of a fictitious
conceptional aid. This very useful tool is a great assistance to performing
field computations for helices and solenoids. Kraus has shown that a loop of
electric current, i.e., electric charges flowing around the circumference of
the loop produces the same radiation fields as those of a flow of a
fictitious magnetic charges moving up and down the axis of the loop. The
fields external to a helically wound solenoid can be found by assuming a
flow of electric charges around the helix, or by assuming a flow of magnetic
charges moving along the axis of the solenoid. The latter computation is
much simpler to perform analytically than the former".
The word vector potential is not used but in a formula illustrating this we
have.
AR = (|E subscript theta| / |E subscript phi|) [The = sign has a delta
sign over it - whatever that means.]
The purpose of quoting this formula is not to try to blind you with science
but to show that our mysterious A has popped up again.
Regards,
Peter, G3LDO
<[email protected]>
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