[Milsurplus] Trans Oceanic MW reception

[aGEnuine ham]

Gary:

I think Hue is guilty only of a poor choice of words and grammatical
expression.  He was asking about  radio propagation over salt water.  Not
about Zenith radios.

And, I haven't seen an answer, so I pulled my copy of "Principles of
Aeronautical Radio Engineering" by Sandretto, published in 1942 out of my
library.  Based on late 30's practices.  Lots of references to 30s IRE
and CAA papers and tests.  Well, the answer is in there, in the equations
and graphs, but I didn't take the time to carefully grind through them. 
One minor problem is that he emphasizes the case of heavy noise
conditions, which of course, shortens the range considerably.  As a knee
jerk reaction, I think MW reception *might* have been marginally
possible, but DF definitely not.  One question which I have never seen
addressed is what the propagation conditions over the Western Pacific
were THAT SPECIFIC DAY, and what was the gray line enhancement (on 3 MHz)
at that time of day in that location ON THAT PARTICULAR MORNING.  And, we
will never know, because it was not measured back then.  Using calculated
propagation conditions, even based on accurately known sunspot numbers,
is only good for an answer within an order of magnitude for present
applications, so how could conditions back then be accurately determined
+/- 10% based on the modest data available.    If someone turned up a
daily log of some MW DXer on Hawaii for July 2, 1937, then we might get
somewhere.  Failing that, anything could be postulated, (and almost
everything has been) and the necessary conditions for the wanted result
derived.  Circular logic at its best.

Sandretto says around 50 microvolts per meter is necessary to overcome
heavy static.  Receiver bandwidth dependent, but not receiver sensitivity
dependent.  Go to the FCC field strength calculations for salt water and
see at what range a 10 KW station produces 50 microvolts per meter, and
then extrapolate for quiet conditions.  But wait, hasn't one of the
investigations turned up records indicating that there was a thunderstorm
nearby?  In the tropics, high noise is likely the case most of the time. 
So, maybe Sandretto knows what he is talking about.

73,
George
W5VPQ

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