[Lf] More on LF history

[hal]

Frank was kind enough to drop off two good radio history books, one
written by the Navy
and the other by authors at the old NBS, now NIST.    It will take me a
bit to go through
them but a quick look-through reveals these facts:   Say that Marconi's
first ship was
equipped by 1898.  By 1924 or so the fact of hf propagation became
widely known and
circuits began moving up there.  Large land-based arc stations did
better with
frequency that was in the tens of kHz. while ship stations did better in
the hundreds
of kHz.   Perhaps there is a physical reason for this?     NBS
investigated LF propagation
over seawater around 1910 and two physicists there coined the first
propagation equation
relating signal strength to distance.  This is the Austin-Cohen
equation.  This equation
related distance for the groundwave.  Later, exponential factors were
added to account
for skywave propagation.  (Andre: there appears to be a lot of early
material on LF still
in the NIST library at Gathersburg and more at Boulder Co.)

There is a note that says that the Navy became interested in using
medium wave above 1.5-3 Mhz.
after WWI because of interference experienced below that.  They appear
to have had many
discussions with ham operators who had been exiled to this region and
who had been using
sky wave modes of propagation's early, before it became generally
appreciated.  So, based on
these discussions they began their own program of investigation and
discovered, too, the
capabilities of this region of spectrum.   Officially, at first, the
Navy was against using these
frequencies because propagation depended upon the time of year.  LF
circuits were constant,
like clear channels, with which ships and shore stations operated
reliably.  HF required frequency
changes, relay stations and training to move messages over comparable
distance.  Both the
British and American military decided to build their own systems and
equipment and turned down
offers made to them from the Marconi Company.  The US Navy build a chain
of 26 LF stations
(I have a list of these if anyone is interested in them) around the
periphery of the US, its possessions
and even nearby foreign countries, mostly in the Caribbean.



--Hal