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. _______________________________________________ IRCA mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: [email protected]
