GB1086808A - Tunable frequency selective circuits - Google Patents

Abstract

1,086,808. Aerial coupling circuits; transistor receiving circuits. WESTINGHOUSE ELECTRIC CORPORATION. April 1, 1965 [April 14, 1964], No. 13864/65. Headings H3T and H4A. The input circuit of a transistorized television receiver is tuned over the entire VHF band by a variable capacity, the aerial and transistor input being so coupled in as to provide constant bandwidth. The aerial 10 is coupled into tuned circuit L1, C1 via balanced to unbalanced transformer 20 and series inductor L2, so as to load the tuned circuit with a resistive impedance proportional to the square of the frequency. The inductor L2 may be shunted with a capacitor (Fig. 2, not shown) so as to narrow the bandwidth somewhat, at the high-frequency end; also the coupling coefficient and secondary inductance of the transformer 20 may be so chosen that leakage inductance provides the necessary inductance (Fig. 3, not shown). The transistor TR is in grounded base connection and is coupled in via a series inductor L3: a shunting capacitor C4 compensates at the highfrequency end of the range for the inductive component of the input impedance of the transistor. A stabilizing resistor R3 shunted by decoupling capacitor C4 is connected in series in the emitter lead. The coupling is made such that the load thrown on the tuned circuit is equal to that from the aerial over the tuning range.