A course indicator of pointer type for the visual radio range-beacon system
Francis W. Dunmore · Bureau of Standards Journal of Research · 1931
A form of tuned-reed radio range-beacon course indicator is described, called a reed convex ter, in which the course indications are not given by observing the two reed motions as heretofore, but by means of a zero-center pointer type indicating instrument.The motion of the two reeds generates small alternating voltages, which when rectified by oxide rectifiers and passed in opposing polarities through a zero-center indicating instrument, serve to give course indications by the deflection of the indicating instrument needle in the direction of deviation of the airplane from the course.The reed converter consists of two reed units, two oxide rectifiers, and the course-indicating instrument.The driving coils of the two units are connected in series to the output of the aircraft radio receiving set.Each reed converter unit consists of a polarized reed tuned to one of the beacon modulation frequencies.The reed vibrates between a set of driving coils which are supplied with the signal from the radio range.The same reed extends between a set of pick-up coils, the motion of the reed generating a voltage in these coils.Since a null method of course indication is used, it is necessary to provide a signal-volume indicator in the form of a 0-500 microammeter in the output circuit of the oxide rectifiers.It is connected so that the output from each recti- fier deflects the instrument pointer in the same direction.It not only serves to enable a pilot to tune in the beacon signal and to control the volume, but also indicates a cessation of this signal or a failure of any part of the radio re- ceiving set or reed converter units.Several forms of converter selector-switch circuit arrangements are shown whereby it is possible to use the reed converter course indicator on any course of a 4 or 12 course radio range beacon.By setting a pointer to the color of the range beacon to be flown and the direction of flight on it, the proper two-reed units are selected by this switch, and their outputs connected in the correct polarity to the course-indicating instrument so that its pointer will deflect in the same direction as the deviation of the airplane from the course.As the course-sharpness indications depend upon the signal level delivered to the indicating instrument, this sharpness may be controlled at will.The combination of this course indicator and the high-frequency fog landing beam course indicator into one indicating instrument is described.This instru- ment, when provided with a suitable switch, may be made to give two more indi- cations; main radio range-beacon course and signal volume indication.The advantages and disadvantages of the reed converter as compared to the tuned-reed indicator are discussed.