Section III
in parallel with the output impedance of V-407B. Any
temperature coefficient. The combination of R -1580
change in the output impedance of V-407B would
and R -1581 has just enough negative temperature co-
cause the frequency of oscillation to change. By
efficient to offset the inherent positive temperature
applying a 30 cps signal to the grid of V-1407B, the
coefficient of C-1401. This balance prevents the
output impedance is changed at a 30 cps rate and hence
oscillator frequency from varying appreciably with
the frequency of oscillation of the 9960 cps oscillator
temperature change. Output of the oscillator is fed to
rises and falls at a 30 cps rate. Sufficient 30 cps
the input of V-1403, a push-pull amplifier driving 30-
cps output transformer T-1401.
signal is applied to the grid of V-1407B to cause the
frequency to rise and fall 480 cps from the 9960 cps
center frequency. * The amount of 30 cps signal
ates a 9960 cps signal frequency modulated at 30 cps.
applied is controlled with the DEVIATION potenti-
ometer R-1421. The 9960 cps center frequency is
See figure 3-2. If a signal is applied to the grid of
stabilized by adjusting the d-c voltage on the grid of
V-1406, the amplified signal in the plate circuit will
V-1407B automatically, thereby holding the output
be shifted by 180. If this signal is shifted another
180 and applied back to the grid of V-1406 in phase
impedance at the proper center value. To accomplish
with the original signal, oscillations will occur. In
this, oscillator output is taken from the cathode of
this oscillator the signal from the plate of V-1406 is
V-1407A and applied to the grid of V-1408A which
serves as an A F C amplifier. The discriminator
applied through a cathode follower to a four section
phase shifting network connected back to the grid of
circuit, consisting chiefly of discriminator transformer
V-1406. The phase shift through the entire four
T-1402 and rectifier V-1409 developes a d-c output
sections is 180 at 9960 cps. Hence oscillations occur
* This represents a deviation ratio of 16 where devi-
at this frequency. If the value of any resistor in the
network is changed the frequency of oscillation will
deviation from center freq = 480 cps = 16
change. The first phase shift section is made up of
ation ratio =
30 Cps
modulating freq
C-1427 and the resistive network consisting of R-1465
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