b. This block diagram of a high level radar modulation system is
similar to the circuit we have been using. We replace the battery with a
high voltage power supply of several thousand volts.
The discharge path
(RL) is replaced by the magnetron and its pulse transformer. An electronic
switch replaces the mechanical switch.
The diode is added to isolate the
high voltage from the switch when necessary. The operation of the PFN and
its circuit is as follows:
(1) At the first instant of time the electronic switch is an open
circuit.
(2) The high voltage power supply charges the PFN through the pulse
transformer primary and the isolation diode V1.
(3) The PFN charges to several thousand volts in two TDs.
(4) The PFN cannot discharge yet because current cannot flow from
plate to cathode through the isolation diode V1.
(5) After the PFN is charged, a trigger spike short-circuits the
electronic switch.
(6) Now there is a discharge path for the PFN, and current flows
through the pulse transformer primary and electronic switch.
(7) After the PFN is completely discharged, the electronic switch is
an open circuit again.
(8) The PFN recharges and is ready to be triggered again.
(9) The PFN is charged and discharged at the PRF of the radar.
17. Charge and discharge waveforms when Rc equals RL.
Notice the two oscilloscopes in Figure 32. One scope is connected
across the PFN and the other scope across the load. Now we can watch the
waveforms across both the PFN and the load.
(1)
Both the PFN and the load are connected to the vertical
deflection
plates of the scopes.
This gives us time reference along the
horizontal
axis and amplitude reference along the vertical axis. The graph
in Part A
of Figure 33 is the waveform of the charging PFN as seen on the
scope. It
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