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In connection with the d.s.b. system described in April QST (Rockafellow, "High-level balanced modulator for D.S.B."), carrier suppression does not seem to be difficult from 160 through 10 meters, but the higher frequencies offer more of a problem. This is probably because of the greater effect of tube capacitances at these frequencies. The method of balance control shown at A in the accompanying figure seems to help this condition at the higher frequencies.
Also, some of the fellows might like a pi-network output tank. The circuit can be rearranged to use one as shown at B. In this arrangement the phase reversal is accomplished in the grid circuit and an additional tuned cirruit is required.
Fig 1. Circuit for adjustment of modulator balance. (A)
and high-level balanced modulator circuit using pi-network output tank (B).
Values in these circuits are similar to those given in April QST.
Stuart Rockafellow, W8NJH.