Improvements in radio receiving apparatus

Abstract

Abstract 449,470. Valve circuits. RADIOAKT.- GES. D. S. LOEWE, 10, Wiesenweg, Steglitz, Berlin. Nov. 24, 1934, No. 33806. Convention date, Nov. 24, 1933. [Classes 40 (iii) and 40 (v)] High selectivity is obtained in a receiver particularly intended for the reception of television signals, by the use of a piezo-electric crystal 12 connected in the intermediatefrequency stage of a superheterodyne receiver. The signals are applied to a twin-grid frequencychanger 7 from the common point of two aerial resistances 2, 3. The intermediate frequency passed to the transformer 10, 11 is higher than the received signal frequency and is transferred to a capacity bridge comprising condensers 13, 14, 15 and the crystal 12. To maintain the mid-point of the transformer secondary 11 at earth potential, the primary winding may be split, each half being coupled to one end of the secondary 11 and the mid-point earthed, Fig. 2 (not shown). By means of the bridge only the resonance frequency of the crystal passes without attenuation to a second frequencychanger 18. To widen the response curve, two crystals having a difference of 5000 cycles may be arranged side by side in the mounting 12, or one crystal may be stepped or ground to wedge shape. The cutting-off of the higher modulation frequencies may be compensated by low-frequency correction circuits in known manner. The second frequency changer 18 reduces the frequency, the output being passed through a frequency-correcting band-filter 21, 22 to a normal receiver 24 for detection and reproduction. The entire apparatus concerned with the first intermediate frequency is carefully screened at 16, 17. Specification 443,046 is referred to.

Inventors

No inventors recorded.

Bibliographic Details