GB611548A - A system for controlling the frequency of oscillators before operating in synchronism, particularly radio diffusion emitters on communal wave lengths - Google Patents

Abstract

611,548. Frequency measurements; synchronism indicators; cathode-ray oscillographs. SOC. FRANCAISE RADIO-ELECTRIQUE. April 30, 1946, No. 13081. Convention date, Nov. 4, 1939. [Class 37] Synchronism of two or more high-frequency oscillators is checked by feeding voltages from each of the oscillators, or voltages resulting from the mixing of these voltages, to a cathoderay oscillograph which is so connected that a stationary image is obtained on its screen when the transmitters are in synchronism, the image rotating in one direction or the other if the frequency of one transmitter differs from that of the other. A pilot station 1, having a wavelength 'corresponding to a frequency Fo=959,000 cycles per second, is connected by a telephone line 2 to a station 3 to be checked. A frequency divider 4 having a ratio of 1/728 converts the frequency Fo to a frequency fo=Fo/728=1317.3 which can easily be transmitted by the line. At the other end of the line 2 the telephone current at frequency fo is passed through amplifiers 5, 6 and stabilizers 7, 8 and thence to a frequency multiplier 9 having a ratio of increase slightly different from the ratio of decrease of the divider 4, e.g. 729, which is the sixth power of 3 and is obtainable by six successive treblings. The value 728 is obtained therefrom by subtracting one unit. The amplifier 6 supplies two-phase voltages at the frequency fo to the two pairs of deflecting plates of a cathode-ray oscillograph 11, causing the spot to describe a circular trace. The checking voltage from the pilot station 1, after conversion to the frequency Fo+fo, is fed to a mixer 12 at the same time as a frequency Fo+# from the transmitter 3 to be checked, e corresponding to the possible frequency difference between the transmitters 1, 3. The output from the mixer 12, at a frequency of fo - # is fed to a gas-filled tube giving short impulses at the same frequency which are supplied to the anode 13 of the oscillograph and produce an instantaneous increase in the diameter of the trace visible as a notch 14. This is stationary if the frequencies of the stations 1, 3 are identical, but rotates in one direction or the other if these frequencies differ and the frequency of the station 3 may be corrected.