Hello Roger, VLF,
Maybe it will give us some ideas of the propagation of such an earth
antenna if i try to receive even lower frequencies on my grabber QTH.
Then we can see if the effective area increases when the frequency goes
down. With the high power PA (H-bridge) i could try
8...7...6...5.......0 kHz and will see where the cut off frequency will
be.
But since i mainly want to concentrate on the dreamers band, the 50km
distance to Michael Oexner is a more important goal for me :-)
Roger, any news from your side? Tnx for bringing up the discussion of
the earth antennas! :-)
73, Stefan/DK7FC
Am 15.07.2010 20:07, schrieb Roger Lapthorn:
This sounds an interesting talk. Where is this conference
being held please?
Perhaps with Heyphones and Nicola systems working in the 40-90kHz
region these antennas do behave differently. At 500kHz I'm convinced
the earth electrode structure behaves as a loop based on the reports
I've received and directionality. I suspect the same is true at 136kHz .
At ELF/VLF I think the earth electrode pair must act in several ways
simultaneously.
(a) As an induction loop. This
certainly ties up with behaviour and loop orientation locally in my
experiments away from buried cables.
(b) As a means of producing a potential difference in the ground for
earth mode (conduction) communication. Again, this is how I understand
my "utilities assisted DX" is being achieved on 838Hz with the signal
being largely conducted along buried pipework and cables and the last
few metres being inductively coupled into my loop receiver. I can't see
how else just 4W can get so far.
(b) As an inefficient and lossy dipole radiating a tiny signal.
It would be most interesting to read about the ELF antennas used for
Project Sanguine and the theory behind these. These (miles long)
antennas were grounded at each end and the grounding was important for
the system to radiate an ELF signal detectable in the deep oceans at
76Hz.
Has Dr Gibson written anything already to give us a clue what he thinks
is going on?
73s
Roger G3XBM
On 15 July 2010 17:52, John Rabson <[email protected]>
wrote:
Members
of the Cave Radio & Electronics Group have been using and
investigating earth loop antennas for some time. The theoretical basis
of such an antenna has not been clear to us, but Dr David Gibson of
CREG is proposing to give the following lecture at the Hidden Earth
conference in the UK this autumn.
How earth-current antennas really work
--------------------------------------
With cave radio equipment such as the HeyPhone and Nicola system there
has been a trend away from the use of induction loop antennas towards
earth-current antennas, i.e. long wires grounded at both ends. However,
the popular explanation for how these antennas work is fallacious. They
do not operate by allowing the current to flow in a 'big loop' in the
ground and in fact, they do not depend, fundamentally, on current flow
in the ground at all.
The fact that the popular explanation is wrong is important because, if
we do not understand how the antenna works, it is difficult to know the
best way to use it, or how to design a better one. Back in 2003, I wrote
an article for the CREG journal entitled 'What We Don't Know About
Earth-Current Propagation'. It has taken me some time to get to grips
with the problem but this talk will now go some way to filling in the
gaps in this knowledge and will describe a method of experimentally
rating earth-current antennas for effectiveness.
--
David Gibson
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM GQRP 1678 ISWL G11088
|
|
