Abstract: Frequency disturbances caused by voltage fluctuations which occur when a bandwidth limiting lag network is switched in and out of a frequency synthesizer circuit to provide the wide bandwidth necessary for fast frequency hopping are eliminated by the invention. Rather than switching a parallel charging source for the large network capacitor out of the circuit during each hopping interval, the capacitor is charged in series to a constant level during narrow bandwidth mode and charged on both plates in consonance with the input voltage during the wide bandwidth mode to thereby render the lag network active during the narrowband mode and transparent during the wideband mode.