Regarding Dave Gibson's thoughts on earth electrodes, I'm puzzled. As Stefan says, the current is returned by a path within the soil/rock and a loop MUST exist. Can the structure be modelled both as a magnetic loop and a electric
dipole?
Hello Roger,
simplified one could state that current causes a magnetic field and voltage causes a electric field.
A small loop antenna is fed by a large current and small voltage and is considered to be "magnetic".
A small vertical monopole (Marconi antenna) is fed by a large voltage and small current and is considered to be "electric".
But lots of antennas (in fact most antennas that are mot small in regard with the wavelength) are fed by a significant current and voltage and can be considered as partly "magnetic" and partly "electric".
I believe that the same is true for an earth antenna.
In regard with this a "mind game":
Assume a small loop, fed at the center of one side but with a switch at the center of the opposite side.
If the swithch is closed the antenna is small (magnetic) loop to be fed with large current and small voltage. A series capacitor is needed to bring this structure to resonance.
If the switch is opened however the antenna becomes "electrical". It has to be fed with a large voltage and small current. To bring it to resonance a series inductor (loading coil) is needed.
What if the switch is replace by an inductor, let's say with a value of half of the loading coil ?
Now it is neither a magnetic loop neither a electric antenna, but something inbetween.
It still need to be brought to resonance with a capacitor, but a much smaller value than needed for the pure loop.
In regard with the pure loop the volatge at the feedingpoint will rise and the current will sink.
73, Rik ON7YD - OR7T
On 22 July 2010 09:15, Markus Vester
<[email protected]> wrote:
Dear VLF enthusiasts,
browsing through saved VLF-grabber screenshots, I noticed some recent changes of VLF MSK-band usage:
2010-06-24 06:00 20.27 kHz (ICV) QRT
2010-06-30 05:00 16.4 kHz (JXN) QRT
2010-07-05 07:05 18.3 kHz (HWU) QRT
2010-07-08 23:00 21.75 kHz (HWU) break for 6 hours
2010-07-10 06:00 22.1 kHz (GQD) switched from 100 bd to 200 bd
2010-07-10 10:00 19.58 kHz (GBZ) QRT
Thus within a couple of weeks, half of the European military signals have gone for good.
Perhaps there is less need for submarine communications in today's world... let's hope that the submarines themselves (along with all that other military hardware) may become obsolete in tomorrow's world!
73, Markus (DF6NM)
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