A Peculiar Type of Rapid Fading in Radio Reception

Abstract

WHILE studying the field-strength variations at Waltair of transmissions from certain broadcasting stations of the All-India Radio, a peculiar type of rapid fading, which does not appear to have been reported so far, was observed during the summer months on the 41- and 60-metre bands. The phenomenon may briefly be described as the apparent existence on the carrier, at the receiving end, of a permanent modulation of 2–3 cycles per second. When the programme is on, there is superposed on it a variation in intensity at frequencies ranging between 2 to 3 cycles per second. This gives the impression of a quivering or fluttering of the transmission. This phenomenon is therefore referred to here as the 'flutter phenomenon'. The effect produced in the loud-speaker by the'flutter' is somewhat similar to the beating of two notes of nearly the same frequency. When the quasi-frequency of the 'flutter' becomes large, it produces a most annoying effect, and listening to a programme becomes almost impossible. The effect is further accentuated by occasional large amplitude of the 'flutter'.