A F Amplifier

Ssb Phasing Network

Fig. 1 5 Little Feller audio phasing network

90* phase difference

Fig. 1 5 Little Feller audio phasing network been reprinted in recent editions of the ARRL Mobile Manual, I he filter, if amplifier, balanced modulator output, and receiving mixer output circuits are shown in Fig. 9, while Fig. 10 is a simplified block diagram of the rig showing how the changeover from "transmit" to 'receive" is accomplished by merely switching B + from one set of tubes to another without disturbing signal-carrying connections except at one point.

Bridge and lattice crystal filters work as well at 455 kc as they do in the 9-Mc region, and existing sideband handbooks give ample information on the design and construction of such units. Like their higher-frequency brothers, these are medium-impedance devices, and passband shape may be most easily adjusted by varying the output load resistance- À typical circuit is shown in Fig. 11. This may be applied to either a transmitter or a receiver by substituting the proper circuit in the block marked "mixer,"

Older texts on SSB devote considerable space to LC filter circuits operating at 50 kc and lower frequencies. These, for all practical purposes, are obsolete today, The sole exception is in the "third method" where sharp cutoff low-pass filters to eliminate everything above 1350 cps are required.

So, having looked more closely at filter circuits, let's ton our attention now to the phasing approach.

Though a phasing unit can operate at any rf frequency, its been customary (since Wes Schum, W9DYV, chose to use it in his pioneering CE-10A exciter) to use a 9,0 Mc carrier. This can then be mixed with a 5-Mc vfo to get either 4-Mc LSB or 14-Mc USB, without switching.

But the first popular phasing exciter did not use 9 Mc, It was the "SSB, fr/' devised by Don Norgaard, W2KU], for G-E Ham News, and it operated at any chosen spot frequency in the 75-meter band.

This little 3-tube unit followed the same basic principles explained earlier; its block diagram appears in Fig. 12, Power output was some 2 watts. Any frequency change necessitated realignment of the rf phase-shift network.

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