transformer primary, out of the PFN, through V4 and into the reverse-current
meter circuit. Oscillations within the PFN quickly reverse the voltage on
the network. This reverse voltage is drained off by V4.
2. The reverse current charges capacitor C3.
When the short period of
reverse-current flow is over, C3 discharges through R3.
The RC time
constant is long enough to maintain a stable current flow through reverse-
current meter, M1.
3. Thus, the reverse-current action of V4 allows the PFN to begin charging
from the same potential each time.
Hence, the modulator output pulse is
always kept at a constant level, thereby stabilizing magnetron operation.
4. Figure 67 shows a basic high-level modulation system with magnetron
load. This circuit is not an actual high-level modulator, but it does give
you some idea of how a practical high-level modulator works.
Follow the
step-by-step circuit action below:
Figure 67.
Review of High-Level Modulation.
a. At the first instant of time, the THYRATRON switch V2 and reverse-
current diode V4 do not conduct.
b. Therefore, the high-voltage power supply charges the PFN through
pulse transformer primary T1, charging diode V1 and charging choke Lch.
85
Previous Page
