GB557563A - Improvements in or relating to ultra high frequency radio signalling systems - Google Patents

Abstract

557,563. Wireless signalling. STANDARD TELEPHONES & CABLES, Ltd., EARP, C. W., and STRONG, C. E. May 22, 1942, No. 7035. [Class 40 (v)] In an ultra-high frequency radio system in which signals are conveyed by keying interruption or amplitude modulation, the carrier wave is frequency-modulated about a mean frequency and at the receiver is heterodyned with a constant frequency substantially equal to the mean carrier frequency. The frequency modulation is a periodic frequency sweep as indicated .in Fig. 2a, the repetition frequency being higher than the highest signal frequency. At the receiver, Fig. 1, the incoming wave is heterodyned by a wave of about the mean incoming frequency and the difference frequency is passed by resistancecapacity couplings through the I.F. stages V<SP>3</SP>, V<SP>4</SP> to a second detector D2. The couplings are such that low frequencies up to about 10 kc. and frequencies above 1 mc. are suppressed, with the result that energy reaches the second detector D2 in the form of pulses at the repetition frequency as indicated in Fig. 2. The width of the pulses is determined by the relative values of the frequency sweep at the transmitter and the band width of the receiver I.F. stages. The pulses may be passed through a valve V<SP>5</SP> with an output circuit tuned to the pulse frequency, to an output transformer T. The heterodyne may be provided by a crystal oscillator V<SP>1</SP> with its plate circuit tuned to a harmonic of the crystal frequency and feeding a harmonic generator V<SP>2</SP> giving a further multiplication of frequency in the circuit C<SP>1</SP>, L<SP>1</SP>. A resonant concentric line CTL is tuned by a condenser C<SP>2</SP> to the mean carrier frequency, and the incoming carrier and the oscillation in C<SP>1</SP>, L<SP>1</SP> are both applied to the line and to a diode D<SP>1</SP>, the beat oscillation being developed across the resistance R<SP>1</SP>. The wave form of the frequency modulation may be sinusoidal or sawtooth, and the modulation may be effected as described in Specification 556,208.