GB704178A - Improvements relating to frequency discriminator circuits for frequency modulated waves - Google Patents

Abstract

704,178. Frequency modulation. METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. June 14, 1951 [June 16, 1950], No. 14134/51. Class 40 (5) A frequency discriminator comprises coupled primary and secondary circuits tuned to the central frequency of the frequency modulation band with the primary and secondary inductances separately screened magnetically and the coupling provided by electrical connections introducing a portion of the primary circuit into the secondary circuit so as to be common to both circuits, at a mid-point of either inductance or capacity branch of the secondary circuit, and the two electrical connections also applying unequal alternating potentials to the secondary circuit. As shown a capacitor C3 of the primary circuit is introduced into the capacity arm of the secondary circuit between the equal capacitors C2". The demodulated output from the diodes D1, D2 has extreme values between frequencies whose spacing is dependent on the smallness of the capacitor C3 and between these frequencies the demodulation is linear. Alternatively a fraction of the primary inductance L1 may be connected through D.C. blocking capacitors to points of the secondary inductance L2 equidistant from a balanced mid-point.