3-30
The blocking oscillator discussed is a free-running circuit. For a fixed prf, some means of stabilizing
the frequency is needed. One method is to apply external synchronization triggers (figure 3-37), view (A)
and view (B). Coupling capacitor C2 feeds input synchronization (sync) triggers to the base of Q1.
Figure 3-37A.—Blocking oscillator (synchronized).
Figure 3-37B.—Blocking oscillator (synchronized).
If the trigger frequency is made slightly higher than the free-running frequency, the blocking
oscillator will "lock in" at the higher frequency. For instance, assume the free-running frequency of this
blocking oscillator is 2 kilohertz, with a prt of 500 microseconds. If sync pulses with a prt of 400
microseconds, or 2.5 kilohertz, are applied to the base, the blocking oscillator will "lock in" and run at 2.5
kilohertz. If the sync prf is too high, however, frequency division will occur. This means that if the sync
