A momentary digression from the topic...
Who ever saw a DF loop located that way. How did they steer it? With their feet?
Not being sour, just a thirst for the truth and what I saw was not a DC-3.
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[FONT=verdana, Arial,Helvetica]Radio Direction Finding[/FONT]
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There are several types of equipment under this general head. In each case, however, use is made of the directional characteristics of a loop antenna. The loop may be either fixed or rotatable. [/FONT][FONT=verdana, Arial,Helvetica]
The LF radio-range system had two principal drawbacks: it provided no information on the aircraft's position nor whether it was flying to or from a beacon. If a pilot were flying along a known airway he could extrapolate the to/from situation with a drift off course slightly to pickup the "A" or "N," then deduce from the charts whether the beacon was in front or behind him. [/FONT]
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A number of maneuvers were available to a pilot to eliminate the ambiguity of which direction the beacon was relative to his heading, or to determine which quadrant of the radio range he was within, or identify which beam of the range he was intercepting. These maneuvers had names such as the 90° turn method and the parallel method. Useful as they were, they each required a significant deviation from the aircraft's [/FONT] [FONT=verdana, Arial,Helvetica]
intended course, sometimes even a 180° turn away from the station.[/FONT]
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The Radio Compass was the first glimmer of hope in determining bearings to a radio station, of filling the information void of the four course radio range. It added a fixed loop antenna and visual indicator to the receiver system. With this system, as long as the aircraft was headed directly toward a radio station the needle of the indicator remained centered; headings to the right or left of the station resulted in a corresponding deflection of the needle. [/FONT]
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The radio compass was chiefly used as a "homing" device, and bearings of radio stations off the line of flight could be obtained only by turning the aircraft toward the station and noting the magnetic compass heading when the needle was centered. [/FONT]
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Replacing the fixed loop antenna with a rotatable loop eliminated this cumbersome maneuver. This system was called a Radio Direction Finder. With the rotatable loop, bearings could now be obtained without turning the airplane itself. The pilot or navigator would rotate the loop, usually mounted on the fuselage below the cockpit, to the position of minimum signal strength, or "null." The bearing to the radio station was then read from a graduated, mechanical dial.
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The Automatic Direction Finder, a marvelous invention, followed the RDF. Finally, a self-contained apparatus for aircraft navigation was available. Gone were rotatable loop antennas and guess-work readings from mechanical azimuth dials. The ADF indicator needle always points directly towards the beacon, which now could be a Non Directional Beacon—NDB"[/FONT]
http://www.navfltsm.addr.com/ndb-nav-history.htm
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For visual reference of a couple of variations:[/FONT]
http://www.airliners.net/photo/Douglas-R4D-6-Skytrain/0234751/&sid=cb45c9e52920946994ec248a941ccaac
http://www.airliners.net/photo/Swis...0244464/&sid=cb45c9e52920946994ec248a941ccaac
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So, to determine the type of antenna and it's location, it's first necessary to determine the type of radio equipment installed on the aircraft (has nothing to do with the version of a/c but in many cases it does reflect on the original purchaser's requirements). As aircraft were often field-modified or spec'd. for different equipment during a production run, well...[/FONT]
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BTW, a modern ADF antenna is a flush-mounted flat box, often no larger than a poor man's wallet, and hardly noticeable on quick inspection.
Rob
Now, we return you to the program in progress...
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