3. Part B of Figure 54 shows the discharge cycle.
The closed switch
becomes a short-circuit across the PFN.
Therefore, the PFN discharges
rapidly through the load, forming a rectangular pulse. The reason the pulse
is rectangular is that the PFN discharges through a load resistance equal to
the characteristic resistance of the line.
Thus, the pulse amplitude is
3,000 volts DC, half the voltage to which the PFN is charged.
The pulse
width is equal to two TDs.
4. So you see, the rectangular pulse used to trigger the magnetron into
oscillation is actually formed during the discharge of the PFN and at a high
power level.
Because of the high voltage at which it must operate, a
conventional ATL cannot be used. The capacitors in the line would have to
be very large to withstand the high voltage.
So, a specially-constructed
ATL is used, called a Guillemin line.
5. Figure 55 shows the schematics of two types of Guillemin lines used
frequently in radar modulators.
The network in Part A simulates the
characteristics of an open-end transmission line. Notice that the coils and
capacitors in the individual sections are in parallel. A single capacitor,
Cst, stores the entire high-voltage charge.
The L-C circuits develop
oscillatory voltages which add to the voltage of the storage capacitor Cst
during the discharge cycle.
The oscillatory voltages make the network
voltage fall to zero in two equal steps.
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