Resistance Tuning

Abstract

Resistance tuning is analyzed postulating the absence of inter-stage reaction and grid conductance. Reactance tuning is also analyzed under these same conditions. Formulas are developed by which it is possible to compute both the amplification and selectivity it is possible to attain in both cases. The fact is brought out that if we desire to attain a maximum of selectivity (and therefore a minimum band width causing improvement in the signal-to-static ratio) without undue sacrifice in the audio quality of reception and to maintain this same "optimum" compromise over the entire tuning range, it is of importance to keep the value of inductance divided by effective resistance in the circuits equal and unchanged over the entire tuning range. With reactance tuning this is not feasible. With resistance tuning it might be feasible. Using a minimum of two resistance tuned stages, consisting of tuned antenna and coupled by a tube to a second tuned circuit, and assuming both side bands are to be received, a possible amplification as great as 430,000 between antenna and detector grid with adequate selectivity is indicated. With reactance tuning we would probably be forced to use additional stages to attain this result. For this reason the substitution of resistance tuning for reactance tuning might result in considerable economy of both apparatus cost and space occupied. Resistance tuning has an advantage over reactance tuning in that without making circuit changes, we may tune in any frequency lower than the maximum frequency which the set can receive.