Radar System Engineering

542 THE REG’EI VI.VG SYSTE,JI—I.VDICA TORS [SEC. 13.17
and is therefore proportional to the time integral of E. When E reaches
the desired maximum value, the switch is closed and V1 is disconnected.
The sudden termination of its current results in an oscillation of L and its
associated capacity. The plate end of the inductance swings positive,
disconnecting V, as the potential rises past the 200-volt level. On the
down-swing, V2 becomes conducting again and clamps the inductance to
the 200-volt point, resulting in the waveform shown. The amplitude of
the oscillation is dependent upon the energy stored in the inductance at
the end of the sawtooth, which in turn is determined by the current and
hence by the “area” under the sawtooth. It can be rigorously proved
by analysis that this amplitude must be such that the average voltage
across the inductance (neglecting its resistance) is zero during the waveform.
We shall be content with the general statement that this must
be so since, in the absence of resistance, the average potential across
an inductance during a completely closed cycle must be zero regardless of
waveform. Therefore in this case the initial, the average, and the final
values of the waveform are identical and it is “balanced” as desired.
A complete circuit using this method is illustrated in Fig. 13.50. The
Miller circuit is switched by the double-diode clamp Vs, Vi, which in turn
is controlled by the cathode-coupled flopover VI, Vj. The latter is
automatically terminated at a fixed sawtooth amplitude by the signal
passed through the biased diode Vs. The Miller circuit is like that
described in connection with Fig. 1349, except that V, (V, of Fig. 13-49)
is biased somewhat below 200 volts, thereby introducing a small correction
to take care of inadequacies in the response of the deflection system.
The potentiometer P1 allows a wide variation in the sweep speed used,
and Ps adjusts the pattern to proper size.
The amplifier uses negative feedback of a signal taken across a resistor
in the transformer secondary, thereby correcting for deficiencies in transformer
response. In contrast to previous cases, the final stage of the
amplifier is driven negative during the actual sweep; thus the induced
voltage on the plate is positive and the tube does not “bog down. ” The
high potential needed for quick recovery ~vhen the current is rising again
is provided by the joint action of L1 and Cl. During the saw-tooth a large
positive voltage is induced in L1, and Cl is charged accordingly. When
the current derivative reverses at the end of the sawtooth, the voltage is
temporarily maintained at a high level by C,, and, in spite of the induced
voltage across the transformer, the plate of the tube remains at a workable
voltage level during the rapid back-swing. The choice of polarities
is such that the interval in which Cl aids the plate supply is short.