Section IV
Paragraphs 4-49 to 4-53
tune the secondary to 9960 cps. 9960 FM FREQ con-
4-51. 30 CPS OSCILATOR V1401B, V1402A AND B.
trol C1434 adjusts the center operating frequency of
(See figure 4-18. )
the discriminator which in turn controls the center
4-52. The30 cps osci11ator isan RC osci11ator using
frequency of V1406. When V1406 is operating witha
three stages each having again of approximate1y two.
B conduct equally and equal but opposite voltages are
Each stage is coup1ed to the next stage by a phase
developed across R1471 and R1472 giving no voltage
shifting network which wi11 shift a 30-cps signal 60.
in the output, When the V1406 frequency decreases,
A signal at the grid of V1401B will appear at the plate
V1409B conducts more heavily than V1409A and a pos-
of V1401B shifted 180". This signals coupled through
itive afc voltage appears in the output. This positive
a phase shifting network comprising C1402 and R1405
voltage is filtered by R1474, C1430 and R1475 to re-
which shifts the signal another 60. V1402A shifts the
move the 30-cps component and fed to the grid of fre-
signal another 180 and C1403 and R1408 shift it
quency modulator V1407B (figure 4-16). A positive
another 60. Therefore, the signal appearing at the
voltage on the grid of V1407B increases its cathode
grid of V1402B shifted 480 from the signal on the
currentor decreases the output impedance of V1407B.
grid of V1401B. V1402B shifts the signal 180 and
The decrease in output impedance will increase the
C1401 and R1401 shift the signal 60. This gives a
frequency of V1406 so that it oscillates 9960 cps.
total phase shift of 720 and the signal fed back to the
grid of V1401B is in phase with the original signal and
4-50. When the V1406 frequency increases, V1409A
the circuit will oscillate at 30 cps.
conducts more heavily than V1409B and a negative afc
voltage appears across R1471 and R1472. This nega-
tive voltage, fed to the grid of V1407B will decrease
its cathode current or increase its output impedance.
temperature compensating network connected in se-
Therefore, the frequency of V1406 will decrease so
ries with it. The parallel combination of R1580 and
that it oscillates at 9960 cps.
R1581 is used to temperature compensate the C1401,
