GB870238A - Stabilising frequency conversion system - Google Patents

Abstract

870,238. Frequency changing circuits. COLLINS RADIO CO. Nov. 10, 1959 [April 13, 1959], No. 38088/59. Class 40(6) A frequency stabilizing system includes a frequency mixer 11, and a stabilizing frequency generator 14 having an output connected to an input of the mixer, the received signal to be stabilized f t being connected to a second input to the mixer 11. The stabilizing frequency generator comprises a first oscillator 25 having three outputs, the first being fed into a mixer 29 which has as its second input the received signal f t . The difference frequency output from the mixer 29 is fed into mixers 17, 18 which receive, as their second inputs, outputs from a reference oscillator 19 having a frequency #o, and the outputs of these mixers are fed together with the other two outputs from oscillator 25 into modulators 26, 27. Two 90 degrees phase shifters for example 20, 28 are provided to give a 90 degrees phase difference between the inputs to the two modulators (for example as shown the two inputs to modulator 27 are both phase advanced by 90 degrees) and the outputs of the two modulators are linearly combined (e.g. by a resistor) to give an output of frequency f t -f o . This signal is the output from the generator 14 which is fed into the mixer 11 to result in a final output at a frequency #o. The output from mixer 11 may be heterodyned with a further output from oscillator 19 to provide a detected output (Fig. 3 not shown). If the input signal f t carries modulation a bandpass filter 31 may be provided to pass only the carrier, and a limiter 30 may also be provided in the input to mixer 29. Low-pass filters 16, 22, 23 may preferably be provided in the generator to select the required output components from the mixers.