Section IV
Paragraphs 4-53 to 4-59
4-57. VARIABLE PHASE SHIFTING NETWORK.
R1401 phase shifting network. R1582 and R1583 com-
(See figure 4-20.)
pensate C1402 and R1405. R1584 and R1585 compen-
sate C1403 and R1408. Thermal resistors R1581,
R1583 and R1585 have a negative temperature coeffi-
4-58. During VOR operation the 30-cps signal may
cient and R1580, R1582 and R1584 have a negligibly
l o w temperature coefficient. The combination of
be shifted in 45 steps with respect to the 30-cps ref-
erence signal of constant phase that frequency modu-
these two resistors has enough negative temperature
coefficient to offset the inherent positive temperature
lates the 9960 cps oscillator. The phase shifting net-
coefficient of the phase shifting network. This balance
work, comprising R1422, R1423, C1405 and C1406, is
prevents the oscillator frequency from varying appre-
so proportioned that its resistance is equal to its ca-
ciably with temperature change.
pacitive reactance at 30 cps. VOR switch S1401A and
B connects the resistors and capacitors of the phase
4-54. Dual potentiometer R1410A and B in series with
shifting network in different arrangements across the
the first two phase shifting networks allows approxi-
secondary of T1401 (figure 4-21) to shift the phase as
mately 1 cps change in the oscillator frequency and
required. The output of the variable phase shifting
is the 30~ FREQUENCY adjustment. Fixed bias for
network is fed to the grid of cathode follower V1401A.
the three stages is supplied from a voltage divider,
VOR TRACK potentiometer R1422 allows for a small
comprising R1486 and R1487, across the regulated B+
variation in the network resistance for adjustment.
supply. The 360-cps output is taken from the plate
Fixed bias for cathode follower V1401A is taken from
and cathode of V1402B giving two outputs each 180
voltage divider R1498 and R1497 across the regulated
out of phase for driving 30-cps amplifier V1403, a
B- supply.
push-pull amplifier.
4-55. 30 CPS AMPLIFIER V1403.
4-59. Due to the various arrangements of the phase
(See figure 4-19.)
shifting network for different positions of the VOR
switch, the signal at the grid of V1401A does not have
4-56. The output of 30 cps oscillator V1402B is cou-
the same amplitude on all positions of S1401. To keep
pled through C1439 and C1438 and developed across
the V1401A output constant, S1401C selects different
voltage divider R1403 and R1415 in the V1403A grid
points in the cathode circuit of V1401A in such a way
circuit and voltage divider R1414 and R1413 tn the
as to make the 30 cps variable phase output signal
constant for all VOR switch positions. VOR ZERO
V1403B grid circuit. The equal but out of phase sig-
control in conjunction with C1415 allows for zeroing
nals are taken from the voltage dividers and fed to the
grids of V1403A and B. The 30-cps signal in the out-
the circuit during calibration. The output is taken
put is developed across transformer T1401 and cou-
from 30~ LEVEL control, which allows for amplitude
pled through it to the variable and reversible phase
adjustment of the signal, and fed through isolating re-
shifting networks. The 30-cps output of V1403A is also
sistor R1445 to AUDIO SELECTOR switch section
fed to the 90 cps and 150 cps circuits V1405 and V1404.
S1402B.
