GB1124751A - Distance ranging equipment - Google Patents

Abstract

1,124,751. Echo-ranging by electromagnetic or ultrasonic waves. NATIONAL RESEARCH DEVELOPMENT CORP. 31 March, 1965 [31 Dec., 1963], No. 51458/63. Heading H4D. In a blind-aid system in which a transmitted signal comprising time-spaced pulses of a frequency-swept ultrasonic or electromagnetic carrier wave is heterodyned with its reflection from an object to derive a first beat signal representing a combination of range and speed of the object towards or away from the point of ranging, a second signal is also transmitted and from its reflection and the first beat signal is derived a final signal representing range with only a small error due to speed. In a first embodiment (Fig. 5, not shown) pulses having frequency sweeps which are equal but in opposite directions (Figs 1 and 3) are transmitted by transducers (T 1 , T 2 ) driven by sources (S 1 ), (S 2 ) respectively, and their reflections are mixed with counterparts of the respective transmitted pulses to give first and second beat signals (Figs. 2 and 4) whose sum, representing object range with only a small error due to speed, and difference, representing object speed, are obtained at the output of a mixer (M 3 ). The reflected signals may be mixed directly to provide a further signal indicating direction of movement of the object, their sum frequency being greater for an approaching object than for a receding object. Audio tones representing object range, speed and direction of movement may be fed to a blind subject in the intervals between successive transmitted pulses. In a modification (Fig. 6, not shown), the sources (S 1 , S 2 ) are replaced by two synchronously varied delay units (DT 1 , DT 2 ) fed from a single continuous wave (CW) source for producing the two frequency-swept transmitted signals, and the signal representing object speed is obtained by mixing the two reflected signals with a derived signal of frequency equal to twice that of the CW source. To prevent confusion due to beat signals in the audiorange when the two transmitted frequencies are nearly equal, i.e. in the interval t 1 to t 2 , (Fig. 4): (a) the upward and downward fre quency sweeps may be interlaced and a magnetic tape used to delay one beat signal with respect to the other to enable the two beat signals to be combined, (b) different frequency bands may be used for the upswept and downswept signals, with appropriate frequency-multiplication of one beat signal before its subsequent combination with the other beat signal, or (c) a series of mono-stable gating circuits (Fig. 7, not shown) may be used to suppress all received signals in the intervals t 1 to t 2 . In a second embodiment.-The first transmitted signal is the downswapt FM signal of Fig. 1, and the second transmitted signal is a CW signal of fixed frequency equal to half the mean frequency of the transmitted FM signal. The Doppler frequency shift of the second signal provides the signal indicating object spead, and the error due to speed in the range signal derived by heterodyning the reflection of the FM signal with its transmitted counterpart is compensated for by beating the range signal with the second signal frequency-doubled. In the embodiments, Hall effect devices may be used to obtain sum and difference frequencies from two input frequencies. A magnetic tape may be used to provide the tone signals fed to the blind subject, to provide the sources (S 1 and S 2 ), and may replace some of the monostable gating circuits. A tape loop may be arranged to feed continuous tones, rather than bursts of tones, to the blind subject. In embodiments employing ultrasonic waves, a single transducer may be used for the transmission and reception of both sets of signals. In embodiments employing electromagnetic waves, frequency division may be required to bring the range, speed and direction signals into the audible region of the frequency spectrum. A binaural embodiment, employing transducers mounted in a spectacle frame, provides directional information about an object. Examples of transmitted frequencies are given.