GB470450A - New and improved high-frequency electric signal-selecting systems - Google Patents

Abstract

470,450. Wireless receiving-circuits. HAZELTINE CORPORATION. Dec. 23, 1936, No. 35257. Convention date, Jan. 28. [Class 40 (v)] The width of one sideband is automatically adjusted, independently of that of the other sideband, and inversely in accordance with the amplitude of undesired signals on frequencies near the desired frequency and at the same side thereof as the adjusted sideband. The intermediate-frequency band-selector 14 of a superheterodyne receiver comprises a transformer 25, the primary 26 and secondary 27 of which are tuned to the I.F. and are magnetically coupled and capacity coupled by condensers 30, 31 to the junction of which are connected two parallel paths to earth, one over condenser 32, the other over condensers 33, 38 and valve 36 which forms an adjustable shunt impedance to the coupling 30-31. The total sum of the reactances of condensers 30, 31, 32 and 33 should be greater than the minimum apparent resistance of valve 36. The inductive coupling comprises a link circuit 34, 35 which is similarly shunted by a variable impedance constituted by valve 37. The last intermediate frequency coupling preceding the second detector comprises a tuned transformer 17, the primary circuit of which is split to provide input connections to a pair of systems 44, 45, the former being tuned by circuit 47, 48, 49 which has a response characteristic with a peak at about 10 kc. above the I.F., while system 45 has a peak response due to circuit 47a, 48, 49 at a frequency 10 kc. below the I.F. The amplifiers 46 feed diodes 50, the load-resistances 57 of which constitute the biassing sources of valves 36, 37. Thus an interfering carrier, the l.F. of which lies above the desired I.F: increases the conductance of valve 36 and reduces the capacity coupling 30-31, reducing the band width and simultaneously lowering the mean resonant frequency of the selector 14, virtually contracting the upper sideband. Similarly, in the case of an interfering I.F. carrier below the desired I.F., the inductive coupling 34, 35 is reduced by valve 37 and the lower sideband is contracted. Where interference is present on both sides, the bands are contracted unequally in proportion to the amplitudes of the interfering signals.