Radar System Engineering

500 THE RECEIVING SYSTEM—INDICATORS [%C 13.7
The drop in its current further reduces the bias on VI, and there is a
violent regeneration which ends with V1 full on and the grid of Vz far past
cutoff. The grid of Vz then experiences an exponential recovery toward
B+, and when the cutoff point is reached regeneration occurs in the
opposite direction and restores the initial condition. The circuit has the
marked advantage that the time for the fhp-flop action is remarkably
linear with the bias voltage of g,, so that by means of an accurate potentiometer
controlling this voltage a linear timing circuit of rather low
precision can be made. The circuit can be somewhat improved over that
shown in Fig. 13”16 by the addition of a biased diode in the grid circuit of
Vz to determine the precise limit of the negative excursion of that grid.
510 fl/lf
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Negat,ve tr!gger Input
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FIG. 13.17 .—Phantastron delay circuit.
The cathode-coupled multivibrator can also be used in the form of a
freely running oscillator, a flopover, or a scale-of-two, but the Eccles-
Jordan form is most common for such purposes.
The Phanfasb-on.-The phantastron of Fig. 13~17 is a flip-flop of a
quite different type which serves as a timing circuit maintaining its
calibration to about one per cent. In the normal condition, V1 is
quiescent, with the cathode sufficiently positive to cut off the second
control grid so that all of the current goes to the screen. The plate
potential is determined by the setting of the delay potentiometer. If a
sufficiently strong negative trigger is supplied through Vz to the first grid,
the fall in the cathode potential turns on the second control grid. The
establishment of plate current further reduces the potential of the first
control grid so that the second grid is turned full on. The plate can now
fall farther only as the potential of the first grid rises, by discharge of Cl
through R,. The condenser C, acts as a feedback condenser, assuring
linearity of the tube response so that the plate falls linearly with the
time. When the plate reaches the potential of the second grid it no