Let me add a few tidbits here as a nice discussion on sea gain seems to
have begun.
At 24 kHz, vertically polarized signals become pretty much unreadable
with the best technology about 25 feet under the surface. Horizontally
polarized signals do much less well. At 130 kHz the distance would be
less. While it is remarkable that the signals penetrate at all, most of
the signal is reflected or absorbed. In our case I think we can neglect
the component that penetrates down.
I suggest a model of a perfectly reflecting surface and sum the incoming
waves accumulating into a coherent surface wave. Look at how the signal
strength would be by looking out from the receiving antenna at zero
degrees elevation. It is like summing a large number of samples where
many tend to add and not so many subtract.
Then modify that model to account for wave tilt due to the imperfect
conductivity of the sea water as the wave tilt will limit the length of
surface that is reflecting. In the case of sea water that length will
be quite long if these waves can make it all the way from NY City to the
Outer Banks on surface waves.
Wave tilt is not covered in many modern texts but was topic for study
with a few hardy souls such as Hund in his book on RF measurements back
in the early 1930s. Hund dropped the subject in his secon revision. I
would be happy to forward that section of his text as it seems to be a
lost concept, at least over here in the US.
The whole subject of sea gain deserves some attention and discussion.
Frank K0BRA
Alberto di Bene wrote:
captbrian wrote:
Franks interesting bit about reception in NC refers to 770khz - a
long way
from 136 - which in turn is a long way from the navy/submarine freqs.
(anyone know what the navy freqs. are ? )
From the site of Renato Romero (
http://www.vlf.it/submarine/sbmarine.html ) :
----
Signals directed to atomic submarines in immersion. USA and Russia
transmit in the ELF band generating
a slow binary code. Frequencies are 76 Hz for the U.S. system and 82
Hz in the Russian system; the E.R.P.
(Effective Radiated Power) is small, probably a few Watts, but signals
are receivable around the world.
----
Note : they are 76 and 82 Hertz, not kilohertz...
73 Alberto I2PHD
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