GB683942A - Improvements in apparatus for transmitting and receiving radio oscillations - Google Patents

Abstract

683,942. Radio transmitting-receiving apparatus. SOC. FRANCAISE DES TELECOMMUNICATIONS. Aug. 22, 1947 [June 12, 1946], No. 23286/47. Class 40 (v). [Also in Group XXXV] A radio transmitter-receiver includes a receiver portion which comprises a frequency changer having a crystal controlled oscillator and a device adjustable to operate within a narrow band of frequencies, adapted to produce a control voltage which varies as the difference between the intermediate frequency and the frequency to which the device is adjusted, and which is used to stabilize the frequency of the transmitter. In Fig. 1, incoming signals are mixed with oscillations from crystal controlled oscillator 53, and the intermediate frequency is then mixed with oscillations from a low frequency, continuously adjustable oscillator 56, the resulting second intermediate frequency being detected and applied to audio frequency amplifier 46. The receiver may be tuned to any frequency in a wide continuous band, and the variable frequency oscillator is adjustable over the interval between successive harmonics of the crystal-controlled oscillator, so that a fixed second intermediate frequency may always be obtained. The second intermediate frequency is also applied to a discriminator 58 so that a control voltage output is obtained from the discriminator if the second intermediate frequency departs from its predetermined value. The local transmitter 49, 50, is adjusted to have approximately the same frequency as that of the receiver, and during local transmission, part of the energy from the transmitter is applied to the receiver, the control voltage from discriminator 58 being applied to a reactance tube 48 associated with the transmitter oscillator circuit to maintain the transmitter frequency constant and equal to the nominal reception frequency. Instead of providing a second mixing stage and variable oscillator, the first intermediate frequency may be applied to a discriminator, the tuning of which is adjustable over the interval between the successive harmonics of the crystal oscillator, so that control of the transmitter may still be effected at any frequency within the wide operating band. The transmitter-receiver may be of the frequency-modulated type. The modulation may be applied to the reactance tube 48 of the transmitter, in which case the control voltage is applied through a time-constant network, or it may be applied to a further reactance tube associated with the continuously adjustable oscillator 56. A portion of the voltage from the discriminator may be applied in opposition to the audio frequency modulation voltage as a form of negative feed-back. Figs. 7 and 8 (not shown) show suitable circuit arrangements. The aerial may be coupled to the first frequency changer, during reception, through the anode-screen capacity of the de-energized transmitting power valve.