Section IV
Paragraphs 4-5 to 4-11
the oscillator from the other circuits in the r-f chas-
for use in calibrating the MICROVOLTS control. The
sis. The plate circuits of V1501A and B contain de-
audio signals obtained from the demodulator appear
coupling filters which prevent r-f from entering the
at AUDIO OUT jack on the front panel for test pur-
power supply. The output is taken from the cathode
poses. The r-f chassis is contained in an aluminum
of V1501A and delivered to r-f mixer V1503.
shield which is insulated from the front panel and
audio chassis as well as from the r-f chassis. This
is necessary to minimize r-f leakage and is broken
(See figure 4-4. )
only at a few carefully selected points. All audio and
power leads are brought out of the r-f chassis through
4-10, Coarse frequency oscillator V1502 is a crystal-
a filter assembly to prevent radiation from the unit on
controlled oscillator connected as a Colpitts oscilla-
the external leads.
tor. The outer knob of the MEGACYCLES control se-
lects the required crystal, whose third harmonic is
used, giving the oscillator a frequency range of 22.125
(See figure 4-3.)
to 28.875 mc in 28 steps of 250 kc each.
controlled oscillator using a twin triode with one sec-
arranged in two banks, one containing crystals for
tion, V1501B, connected as a Colpitts oscillator while
the other section, V1501A, is a cathode follower act-
odd MEGACYCLES positions, the other containing
ing as a buffer stage. The inner knob of MEGA-
crystals for even MEGACYCLES position. Turning
CYCLES control S1501 selects the crystal required
the large outer knob of the MEGACYCLES control
giving the oscillator a frequency range of 4.875 to
rotates a shaft that controls S1502A and S1502B and
5.100 mc in 10 steps of 25 kc each.
in one bank or the other depending
selects a
on whether the selected megacycle frequency is odd
NOTE
or even. This is accomplished by S1503, on the same
shaft as S1502, which connects 21 volts dc to relay
The inner knob will vary the signal generator
K1501 on odd MEGACYCLES positions. When K1501
frequency in steps of 100 kc due to the quad-
is energized, its contacts 2 and 3 close Connecting a
rupling of the r-f signal by r-f quadrupler
crystal from the bank switched by S1502A to the grid
V1505.
circuit of V1502. On even MEGACYCLES positions,
K1501 is not energized and its contacts 3 and 4 close,
connecting a crystal from the bank switched by S1502B
grid circuit of V1501B and fed through coupling ca-
to V1502. Tuning the large outer knob also operates
pacitor C1503 to the grid of cathode follower V1501A.
a slug rack which varies the tuning of seven coils,
The cathcode follower acts as a buffer stage isolating
L1510, L1511, L1503, L1504, L1505, L1506 and
