LED SYNCHROSCOPE

2N3702 BC109 Circuit uses four LEDs to indicate direction of phase error as correct setting is approached when tuning oscillator to standard frequency. Lamps form display that rotates once per cycle at reference frequency, with brightness of each lamp being modulated at frequency of oscillator being adjusted. Dis-play thus appears to have frequency equal to difference between two signal frequencies, ro-tating in direction indicative of sense of fre-quency difference. Mount lamps on smallest possible circle. Diode and LED types are not crit-ical.-R. H. Pearson, An L.E.D. Synchroscope, Wireless World, Sept. 1974, p 321.