GB590506A - Radio relay station - Google Patents

Abstract

590,506. Wireless signalling. MAR CONI'S WIRELESS TELEGRAPH CO., Ltd. Aug. 28, 1944, No. 16348. Convention date, Feb. 12, 1942. [Class 40 (v)] A radio repeater station comprises a source of received high-frequency energy, two oscillators, one producing low-frequency oscillations having a high degree of frequency stability, a modulator for producing sum and difference frequencies from the outputs of the two oscillators, a first converter to which the received. signal and one of the output frequencies of the modulator are applied in order to produce a low intermediate frequency, an I.F. amplifier, and a second converter to which the amplified I.F. and the other output frequency from the modulator are applied in order'to produce a high-frequency output signal at a frequency adjacent to that of the received signal. In a preferred form Fig. 2, a crystalcontrolled oscillator 10 produces a signal of low-frequency,fk, which is mixed with a signal of frequency fc derived from oscillator 14 in a balanced modulator .12 to give sum and difference frequencies fc+fk. The incoming signal of frequency fs and the difference frequency are applied. to the first converter 16 to give a low I.F. fs - fc+fk, which is amplified by amplifier 18. The amplified. I.F. and the sum frequency fc+fk produced by modulator 12 are mixed in the second converter 20 to give an output signal of frequency fs +2fk. In order to avoid clipping of the side bands in amplifier 18 due to variations in ,fc, a back-to-back discriminator 22 in which the characteristics of the halves of the discriminator are as shown in Fig. 3, is used to provide an automatic frequency control voltage to oscillator 14. In a modification Fig. 4, the output fk of the crystalcontrolled oscillator 10 is used to modulate the output of oscillator 14 in modulator 24, which may be a frequency modulator. The modulation index is adjusted to obtain the most favourable relation between the required frequencies, fc+fk and fc - fk, and the other frequencies present in the output of modulator 24. The incoming frequency in this modification is taken to be fs+2fk, and this signal is mixed with the output fc+fk from filter 30 in first converter 16 to give an I.F. fs - fc+fk. The output from amplifier 18 is then mixed with the output fc - fk of filter 32 in second converter 20 to give an output signal of frequency fs for retransmission. In a radio relay system using this type of repeater station, the output frequencies of the individual radio repeater stations may be alternately fs+2fk and fs, while the received signals are of frequencies fs and fs+2fk alternately.