Patent GB-734329-A (GB)
Title: Improvements in or relating to wireless transmission systems
Inventor: SCHINDLER LUDWIG
IPC: H04L1/00
Filed: 1953-07-23
Abstract: 734,329. Frequency-shift telegraphy; valve circuits for harmonic generation; radio receiving circuits. VIERLING, O. July 23, 1953, No. 20543/53. Classes 40 (5) and 40 (6). In a radio communication system particularly for frequency-shift telegraphy, the transmitter carrier, which is suppressed, and the locallyproduced receiver carrier are provided by multiples of the output frequency of identical stabilized oscillators produced by over-modulating adjustable oscillators by said output frequency. In one embodiment, the transmitter comprises a crystal-controller oscillator 2, Fig. 1, operating at 120 kc/s., which modulates an adjustable oscillator 1 in such a way as to give rise to frequencies which are integral multiples of 120 kc/s. The output from oscillator 1 is modulated by a 1000 c/s. tone from multivibrator 4 in a carrier-suppression modulator 3, giving rise to pairs of frequencies spaced by 2000 c/s. The multivibrator is switched by telegraph signals from 1000 to 1500 c/s. so that two pairs of frequencies containing the signal are produced. The group of frequencies having the greatest amplitude is selectively amplified for transmission, in circuit 5. Oscillator 2 may be cut out and the transmitter used as a conventional carrier-suppression transmitter. At the receiver, a crystal-controlled oscillator 12, Fig. 2, operating at 120 kc/s., over-modulates an oscillator 13 to produce a local carrier of 9.12 Mc/s. which is mixed with the incoming signals of 9.6 Mc/s. Œ 1000/1500 c/s. to produce an intermediate frequency of 480 kc/s. Œ 1000/1500 c/s. which is amplified in circuit 15. When the receiver is to be used for normal transmissions the oscillator 12 is cut out. The output of oscillator 12 is also applied to a frequency divider 16, the 15 kc/s. output from which modulates an oscillator 17 which produces a 465 kc/s. output which is mixed in circuit 18 with the output from amplifier 15 to give a signal comprising a group of sidebands of. frequency 15 kc/s.Œ 1000/1500 c/s. The upper and lower pairs of frequencies are selected by filters 19, 20 and demodulated in circuits 21, 22 respectively to which the 15 kc/s. carrier is supplied from circuit 16. The two tone frequencies 1000 and 1500 c/s. from each demodulator are selected in filters 23 ... 26 and fed to limiters 27 ... 30 thereafter to control a collector circuit or relay 40. Automatic gain control is provided by feeding the inputs to the limiters 27 ... 30 through individual rectifiers 45 ... 48, Fig. 3, to a common load resistor 50, providing a control potential for amplifiers 11, 15 depending on the maximum tone signal of the four channels. The output of the I.F. amplifier 15 also provides a control potential, being fed to a rectifier 31 the output of which is fed through the rectifier 49, Fig. 3, and delay bias source 51 to the resistor 50. Interference in any of the channels producing pulses of greater duration than the telegraphic impulses may be arranged to cut off the output of the channel and disable its control voltage output circuit. Thus, for example, in the channel of limiter 27, a relay 76, Fig. 3, is released to perform these functions when valve 72 is cut off, due to valve 64 becoming conductive when condenser 60 is charged above a predetermined potential, by long pulses applied thereto by valve 56, and obtained from the limiter output through rectifier 52.