[IRCA] Mystery tone at 1610, 1020 and WWII

["Gil Stacy" <gilstacy@xxxxxxxxx>]

In the January 2007 QST magazine published by the ARRL, there is an
interesting article regarding the problems of direction finding with loop
antennas during WWII which gives a basis for understanding our experience
in imprecisely pinpointing the mystery tone a few weeks ago.  The article is
titled "How the FCC Helped to End World War II". ( No, it didn't
surreptitiously install BPL or IBOC in Japan or Germany.)  Immediately after
the attack at Pearl Harbor, the Radio Intelligence Division (RID) of the FCC
installed on the Hawaiian Islands monitoring stations of which M. Walter
Maxwell, W2DU, the QST article's author, was a participant.   In addition, a
half mile Beverage antenna was aimed at Tokyo to monitor domestic a.m.
broadcasts. Of greater importance was that on each of the Islands, Adcock
Directional Finder antennas were erected



According to W2DU's article, at the outset of the war, many allied planes
were lost enroute to Hawaii from the mainland US.  Despite using loop
antenna direction finders, many planes were forced to ditch after becoming
"navigationally impaired" (lost).  The problem was that loop DF's are
capable of delivering reliable results only when receiving vertically
polarized electromagnetic energy.  Skywaves, on reflection and refraction
through the ionosphere, become elliptically polarized which causes a
continuous shift in the null obtained by a loop DF as the incoming signal
rotates elliptically during propagation.  The bearings taken by the DFs
beyond groundwave reception range of the a.m. stations in Hawaii were
practically useless.  Having to depend only on celestial navigation had its
own set of problems, especially on cloudy nights and days.  Fortunately, the
previously installed Adcock directional finders were capable of receiving
only the vertical component of a skywave, even though the skywave is
arriving as a rotating ellipse.  The array of Adcocks throughout the
Hawaiian Islands would "df" the aircraft's "lost message" and would
triangulate the plane's location and furnish to the pilot a corrected
bearing.  No more planes were lost because of navigational problems enroute
from the mainland.  However, planes continued to be lost enroute from Hawaii
to the South Pacific.  The US military invited Prose Walker, W4BW, head of
the FCC's Radio Security Center in the Islands, who also implemented the
program using the Adcocks to assist lost pilots, to investigate the mystery.
He discovered that the pilots were using Mercator projection maps.  The
losses were reduced to zero when the pilots were furnished polar projection
maps.



Our efforts to clearly pinpoint the mystery transmitter on 1610 and 1020
without a high degree of accuracy are explained by the history of the FCC's
experience with aviators during WWII in the Hawaiian Islands and South
Pacific.  Fortunately for us, the worst thing that could have happened to us
in our direction finding the tone was inconsequential in the overall scheme
of things.  On the other hand, the best thing that could happen to a WWII
aviator, was to get home in one piece, alive.
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