Patent GB-942373-A (GB)
Title: Improvements in and relating to an oscillator circuit arrangement, particularly for transmitters and receivers for communication systems and navigation systems, and a frequency-modulated telephony transmitter comprising such oscillator circuit arrangement
IPC: H03B5/34
Filed: 1962-07-13
Abstract: 942,373. Frequency generating circuits; radio receiving and transmitting circuits. N. G. KRUSE. July 13, 1962 [July 13, 1961], No. 27084/62. Headings H3F, H3L and H4Q. A frequency generating arrangement comprises two crystal controlled oscillators whose frequencies are close, the difference frequency being obtained in a mixer and applied to a frequency multiplier to obtain the desired output frequency. This is varied by varying the frequency of one or both oscillators, by means of one or more capacitors connected to the crystal concerned; due to the difference frequency being used, the proportional variation in the final output frequency is much greater than the proportional variation in the frequency of the controlled oscillator. In one embodiment the frequency of oscillator 5, Fig. 1, is varied in steps by means of a plurality of crystals 6-11, e.g. giving 11.00, 11.01, 11.02... 11.09 mc/s. Oscillator 1 includes crystal 2 and is continuously tunable by means of variable capacitor 3, e.g. from 10 to 10.01 mc/s. The difference frequency is extracted from the mixer 12 and multiplied, e.g. x 100 in the multiplier 13 to give an output at terminal 14 which is continuously variable, e.g. over the range 100 to 110 mc/s. Another embodiment comprises a transceiver (Fig. 2, not shown), in which the frequency of the first crystal oscillator is variable in steps by means of switched presettable capacitor and that of the second oscillator in larger steps by switching crystals. The arrangement of the switches is such that after switching the first oscillator through a range of frequencies, a further range is produced by contacts placing further presettable capacitors across each of the crystals in the second oscillator. The difference frequency is applied to a. multiplier, the output of which is used both for driving the transmitter and as local oscillations in reception; changeover is performed by a relay including contacts which change the crystal and associated preset capacitors in the first oscillator and so shift the frequency the amount required for the changeover. The Specification also describes a highfrequency transmitter (Fig. 3, not shown) in which presettable capacitors are switchable in series with the crystals of both first and second oscillators, the difference frequency being selected from a mixer, multiplied in a multiplier and then mixed with the output from a second multiplier following a third oscillator comprising a number of switch-selected crystals. The difference frequency is again selected and multiplied to constitute the transmitting frequency. A further arrangement comprises a combined frequency modulation transmitter and receiver (Fig. 4, not shown), with switched tuning. The transmitting frequency comprises after multiplication, the difference between the frequency from a multiplier following a first crystal oscillator, which is switchable between two frequencies, utilizing two alternative series capacitors, and that of a second oscillator. This comprises a switch selecting either of two crystals, the frequencies of both of which can be varied by means of a number of switchable preset series capacitors. Modulation is effected upon the multiplied output of the first crystal oscillator. The receiver comprises a double superheterodyne in which two crystal controlled oscillators are employed. The first is switchable between four preset frequencies by switching presettable capacitors in series with the crystal, and constitutes the second local oscillator. The output from this oscillator is also mixed with that from a second oscillator in which three different crystals can be selected, each of which is tunable to a number of frequencies, using switched series presettable capacitors. The difference frequency is obtained and after multiplication constitutes the local oscillations for the first mixer. A double superheterodyne receiver is also described. In this switch 116, Fig. 5, selects one of five crystals for first oscillator 115, the frequency of each crystal being variable between two values by means of two-way switches 122-126 and series capacitors 127- 136. The output of oscillator 115 is fed to mixer 137 to which is also supplied an output from a second oscillator 138, the frequency of which is determined by one of the two crystals 140, 141 as selected by switch 139. In addition, each crystal may be tuned to one of a number of different frequencies by means of switches 142, 143 and presettable capacitors 144, 145. The difference frequency is taken from mixer 137 and fed to frequency multiplier 146, the output of which constitutes the local oscillations fed to the first superheterodyne mixer 147. The receiver comprises first and second I.F. stages 150, 152 respectively and a second mixer 151, the local oscillations for which are derived from the oscillator 138.