5.
Brief review.
a. The charging impedance
prevents
the
closed
switch
from
short-
circuiting the power supply.
b. Also, the charging
impedance
increases
the
amplitude
of
the
modulator output pulse.
c. DC resonant charging uses an inductor, called a charging impedance.
d. The inductor allows the PFN to charge to voltage nearly twice the
power supply voltage.
A higher voltage across the PFN means a higher
voltage developed across the load when the PFN discharges.
e. A charging diode in series with the charging choke and the PFN
prevents discharge of the PFN until the switch closes. Hence, the charging
diode allows more than one PRF to be used in the radar set.
Learning Event 6:
THE PULSE TRANSFORMER
1. Figure 63 shows that the modulator load consists of the magnetron, V3,
and the pulse transformer, T1.
The magnetron is described in detail in a
later lesson, so there is no need to go into its operation at this time.
The pulse transformer, however, is specially designed and constructed to
pass high-voltage pulses without changing their shape.
To pass pulses
without distortion, a pulse transformer has a ferro-magnetic core, is
closely coupled, and has few turns in its windings. Hence, it is not like
the conventional transformers you studied earlier in the course. Additional
uses of the pulse transformer are:
a. It couples the high-voltage modulator pulse to the magnetron with
minimum power loss.
b. It matches the low-impedance of the PFN to the high impedance of the
magnetron.
c. It steps up the pulse voltage and, thereby, allows the PFN to
operate at a much lower voltage than the magnetron.
d. It isolates the magnetron filament transformer from the high pulse
voltage.
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