High Fidelity Receivers with Expanding Selectors

A high fidelity receiver for general use requires means for continuously expanding or contracting the resultant band width of all the carrier selectors, in order that the best compromise between fidelity and selectivity may be chosen for any given operating conditions. The expanding selector ("XPS") arrangement may be adapted for either unsymmetrical or symmetrical expansion of the resonance curve. Arrangements are described and the relative merits are discussed for both kinds of expansion. A superheterodyne receiver is described, which has a preferred form of symmetrical expanding selector, as wvell as other advantageous features. A tuning and expanding mechanism is described, in which the expansion is adjustable by moving the tuning knob in the axial direction. The mechanism includes an interlock which permits the operator to tune the receiver only when the band width is contracted. The operator is thereby constrained to follow the correct procedure of first tuning with maximum selectivity, and second, expanding to improve the fidelity to the (extent permitted by noise or adjacent channel interference.