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F L I G H T Section 3251 ADF AND LOOP RECEIVERS B. [[underlined]] Limitations and Precautions In Use of Loop Equipment [[/underline]] 1. [[underlined]] Terrain Effect [[/underlined]] - Terrain has many and varied effects on radio aids. Rain or snow in the area may cause a misalignmen of the legs of a range, multiple legs or bent beams. Various types of ore deposits may have the same effects. Range legs lying up a valley or along a range of mountains may also cause multiples, bent beams and misalignments. Even deep grass or a change of level of the subsurface water below a range station has been known to cause a range station to become malfunctioning. When taking bearings in mountainous country, care should be taken if there seems to be any malfunctioning of the range station. There does not seem to be any hard and fast rule as to what the ADF needle will do under these adverse circumstances, Peculiarities of specific ranges in mountainous country may be determined by taking practice bearings during good weather and noting the accuracy of such bearings. 2. [[underlined]] Night Effect [[/underlined]] - During the twilight hours when the Kennelly-Heaviside layer is moving up or down there may be an uncertainty in the movement of the needle as to its settling down. When skip or other phenomena is noticed, use caution in using the loop equipment. 3. [[underlined]] Static Effect [[/underlined]] - Precipitation and dust static has little effect on the ADF needle as long as it is light to moderate. When heavy static conditions prevail, however, the needle may oscillate, hunt or rotate until the charge is released from the ship or antenna. The needle will then turn back to the station to which it is tuned until static charges are built up again when it may again repeat the previous performance. As a general rule, when the aurul signals may no longer be heard, the needle will usually be unreliable. 4. [[underlined]] Effect of Range Loop and Range Adcock Type Stations [[/underlined]] - To fully appreciate the respective effects of the Loop and Adcock type stations on loop equipment, the essential differences between the 2 type stations must be understood. a. [[underlined]] Loop Type Stations [[/underlined]]- The Loop type consists of 2 loops of wire placed at right angles to each other. A radio transmitter feeds energy modulated at audio frequencies to first 1 loop and then the other by an automatic motor-driven switch. This energy is keyed to produce the Morse code signal "N" in the field of 1 antenna and the signal "A" in the field of the other antenna. If it is desired to broadcast voice over this type station, it is necessary to turn off the range signals as this station does not broadcast voice and range in a simultaneous manner. Because of the construction of this type station, it is not dependable beyond a distance of 30 miles after the hours of darkness. When using an ADF on the Loop type station, a large amount of hunting of the needle will occur. This does not seem to be as prevalent when on-course as when in an open quadrant. Extreme caution should be exercised when taking bearings on this type station. 2/1/47 Flight
