. QST . est obtainable,whereas there is some flattening outon the high-frequency side belowabout 60 db. down. The response ofthe circuit of Fig. 2A is somewhat better on thehigh-frequency side but somewhat worse (belowabout 80 db. down) on the low-frequency circuit of Fig. 2C has the steepest obtainableresponse on the high-frequency side but is verymuch the worst of the lot on the low-frecjuencyside, since the response starts to rise again about 8kc. off on the low side (for circuit values to beconsidered later). At 20 kc, component valueslimit us to the use of the type of coupling sh
. QST . est obtainable,whereas there is some flattening outon the high-frequency side belowabout 60 db. down. The response ofthe circuit of Fig. 2A is somewhat better on thehigh-frequency side but somewhat worse (belowabout 80 db. down) on the low-frequency circuit of Fig. 2C has the steepest obtainableresponse on the high-frequency side but is verymuch the worst of the lot on the low-frecjuencyside, since the response starts to rise again about 8kc. off on the low side (for circuit values to beconsidered later). At 20 kc, component valueslimit us to the use of the type of coupling shownin Figs. 2A and 2D, since practical values for Cmare rather high. It can be shown that the coeffi-cients of coupling for these two circuits are k ~ ~j~, and k ■^ — -7^ In general, the best off-channel response will beobtained by the use of combinations of both thesecircuits, as in the circuit of Fig. 3. For maximum-flat response, the circuits should be criticallycoupled; that is, 1^ = Q 32 QST for. not in any way alter the response of thecoupled circuits, since for the case con-sidered, L >» Lm and L » Li(Fig. 5). And because the coil is sur-rounded by a material of very highpermeability, the coupling between thetwo parts of the coil is almost perfectand the circuit approximates an idealautotransformer, transforming imped-ance and voltage. Practical Circuits Fig. 3 —■ Shunt- and series-coupling circuits can be combined forhigh-selectivity interstage coupling. With critical coupling, the flat-topped characterof the over-all response curve is, if anj^thing, im-proved when a large number of stages is general, any degree of selectivity, approachingthe ideal flat-top response, can be obtained b}-using a sufficient number of stages and combina-tions of under-critical and over-critical will be seen later, the anode of the amplifiertube and the grid of the following amplifier stageare tapped down on the inductance L. This does The complete circuit of
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectradio, bookyear1915
