Section IV
Paragraphs 4-40 to 4-49
shifted another 180 and fed back to the grid circuit in
phase with the original signal, oscillations will occur.
C1581 in the grid circuits of V1512 and V1513 is used
In this oscillator, the signal from the plate of V1406
for automatic volume control in the univerter chassis.
is coupled through C 1426 to cathode follower V1407A.
Avc capacitors C1573 and C1585 remove the r-f com-
The cathode follower output in phase wtth its input, is
ponent of the signal and keep the overall gain of the
fed through S1402D rear to the 9960-cps feedback
univerter chassis constant for all settings of the
network comprising C1427, R1465, C1425, R1458,
MICROVOLTS control which varies the amplitude of
C1423, R1456, R1457 and C1421 where the signal is
r-f signal fed to the univerter during GS operation.
shifted 180 at 9960 cps. The shifted signal is applied
The gain of the univerter chassis is also controlled by
to the control grid of V1406 in phase with the original
connecting the screen grid of V1512 to potentiometer
signal and oscillations occur at 9960 cps.
R1544, part of a voltage divider across the B+ supply.
R1544 allows the screen grid voltage to be varied be-
4-45. The first section of the 9960-cps feedback net-
tween approximately 25 and 150 volts and is adjusted
work is connected in parallel with the output imped-
so that the overall gain of the univerter chassis is
ance of frequency modulator V1407B. Any change in
unity.
the output impedance of V1407B would cause the fre-
quency of oscillation to change. A 30-cps signal from
the 9960 FM DEV control is fed to the grid of V1407B.
4-42. INTRODUCTION. The audio chassis (figure
Therefore the output impedance of V1407B is varied
at a 30 cps rate and hence the frequency of 9960 cps
oscillation V1406 rises and falls at a 30 cps rate.
for modulating the r-f carrier. The following audio
Sufficient 30-cps signal is applied to V1407B to cause
signals are produced 9980 cps frequency modulated
the oscillator frequency to change 480 cps on both
at 30 cps, 1000 cps, 30 cps variable phase, 30 cps
sides of the 9960-cps center frequency. This repre-
reversible phase, 90 cps and 150 cps. 9960 and 1000
cps oscillator V1406, an RC oscillator, produces
sents a deviation ratio of 16 where deviation ratio =
deviation from center frequency = 480 cps = 16
9960 cps or 1000 cps depending on the feedback net-
--
30 cps
work selected. The 9960 cps oscillator frequency is
modulating frequency
modulated at a 30 cps rate by frequency modulator
The amount of 30- cps signal applied is controlled by
V1407B during VOR,
9960 FM DEV control R1421. The 9960-cps center
LOC and 9960 FM operation.
The oscillator output is also delivered to afc amplifier
frequency is stabilized by an afc circuit that controls
the bias on V1407B which in turn changes the oscilla-
V1408A through cathode follower V1407A. Afc ampli-
fier V1408A, in conjunction with discriminator V1409,
tor frequency whenever it drffts from the center fre-
stabilizes the oscillator frequency. During 1000>
quency.
operation the afc circuit is not used and the output of
cathode follower V1407A is fed back through the 1000-
4-46. During 1000~ operation, AUDIO SELECTOR
cps feedback network to the oscillator. 30 cps is pro-
switch S1402D connects the 1000-cps feedback net-
duced by a three stage RC oscillator V1401B, V1402A
work to the grid circuit of V1406. The oscillator will
and B and amplified by 30 cps amplifier V1403. The
now oscillate at a frequency of 1000 cps due to the new
amplified output is fed to a variable phase shifting net-
network, comprising C1418, R1453, C1419, R1454,
work and cathode follower V1401A giving a 30 cps sig-
R1455, C1420, R1456, R1457 and C1421, which will
nal that can be shifted in phase in 45 steps. The
shift a 1000 cps signal 180. 1000~ FREQ control
output of V1403 is also fed to a reversible phase shift-
R1455 changes the resistance of the feedback network
ing network giving 30 cps with a reversible phase
and is used to adjust the oscillator frequency to 1000
shift. Another portion of the V1403 output is fed to
cps. When operating on 1000 cps, frequency modu-
saturable reactor L1401 which distorts the signal.
lator V1407B and the afc circuit are not used.
90-cps filter Z1401 passes only the third harmonic
and 150-cps filter Z1403 passes only the fifth har-
4-47. During 1000~ operation, the output is taken
monic of the distorted 30-cps signal. The 90 and 150-
from 1000~ LEVEL control R1464 in the cathode cir-
cps signals are fed to limiters V1405 and V1404 and
cuit of V1407A. The 1000-CPS output is fed to AUDIO
then to the LOC-GS attenuator. The audio signals are
SELECTOR switch section S1402A. During VOR,
all connected to AUDIO SELECTOR switch S1402
LOC and 9960 FM operation, the output is taken from
which selects the required audio signals and delivers
9960 FM LEVEL control R1467. The 9960 FM output
them to a-f amplifier V1408B. The output of V1408B
is fed to AUDIO SELECTOR switch section S1402A.
is fed to the r-f chassis.
During GS operation one section of NAV-GS switch
4-43. 9960 AND 1000 CPS OSCILLATOR V1406,
V1407 thus disabling the circuit.
CATHODE FOLLOWER V1407A AND
FREQUENCY MODULATOR V1407B.
4-48. AFC AMPLIFIER V1408A AND DISCRIMI-
(See figure 4-16.)
NATOR V1409.
(See figure 4-17.)
4-44. Oscillator V1406 generates a 9960-cps signal
frequency modulated at 30 cpe during VOR,
LOC
and 9960 FM operation. During 1000% operation,
V1407A is also fed to the grid of afc amplifier V1408A.
V1406 generates a 1000 cps audio signal. A signal
The signal is amplified and appears across the pri-
applied to the grid of V1406 will be amplified and will
mary of discriminator transformer T1402. The sec-
appear in the plate circuit 180 out of phase with the
ondary of T1402 is connected to discriminator V1409A
control grid signal. If the plate circuit signal is
and B. Capacitors C1437, C1436, C1433 and C1434
