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Page Title:
CHAPTER 4. THEORY OF BROADBAND, CONTROL, METERING, POWER, DISTRIBUTION, AND FREQUENCY SELECTION STAGES |
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|  THEORY OF BROADBAND, CONTROL, METERING, POWER,
DISTRIBUTION, AND FREQUENCY SELECTION STAGES
Section I. BROADBAND RECEPTION AND TRANSMISSION
band Receive
a. Decoded broadband audio is returned
When NOR-BB switch S801 (fig. 20) is
from the decoding equipment to the audio
placed in the BB position (broadband), en-
preamplifier through terminal X of plug
coded received signals from transformer
P801. Contacts 4 and 15 of tr relay K802
T501 (fig. 12) are coupled through cathode
are closed on receive. Voltage-divider re-
follower V802A to the decoding equipment
sistors R829 and R807 attenuate the re-
(not part of this radio set). Decoded sig-
turned audio signal to the proper level.
nals are returned from the decoding equip-
Capacitor C818 provides dc isolation be-
ment to audio preamplifier V803 (fig. 20)
tween the audio amplifier and modulator
where the signals are amplified and applied
and the broadband decoding equipment. The
to audio output stages V805 through V808.
path of the decoded received signal is
through contacts 1 and 2 of NOR-BB switch
S801B, contacts 2 and 13 of K802, contacts
5 and 12 of K801, and contacts 4 and 5 of
a. Detected coded audio signals are cou-
S801B to the low-pass filter that consists
pled from the detector stage through ter-
of R802, C806, C807, and L801.
minal N of plug P801 and coupling capacitor
b. The output of the low-pass filter is
C808 to the control grid of V802A. A por-
connected through contacts 1 and 2 of switch
tion of the detected signal is applied to
S801A and coupling capacitor C809 and
squelch amplifier V801 (para 42). When
R818 to the grid circuit of audio preampli-
squelch relay K801 operates, relay con-
fier V803. The output of V803, developed
tacts 2 and 11 open and remove the ground
across R824 and R843, is coupled through
on the control grid of V802A. Tube V802A
contacts 10 and 11 of switch S801A to the
functions as an impedance-matching trans-
control grids of the second receiver audio
former and couples the signal from the
amplifier V804. The remaining path of the
high-impedance detector circuit to the
received broadband signals is the same as
low-impedance transmission line to the
described for normal audio circuits in
decoding equipment.
b. Resistor R806 is the high grid input
resistance, and resistors R805 and R804
provide the low output resistance load.
on Broadband Transmit
Plate voltage is supplied from the +300-
volt dc (approximately 270 volts on re-
a. Microphone audio is normally coupled
ceive) supply through contacts 6 and 16
of tr relay K802. The output of the broad-
from the front panel or from Radio Set
band cathode follower is coupled to the
Control C-1429/U AUDIO jacks from ter-
decoding equipment through coupling ca-
minal F of plug P801 to audio preamplifier
pacitor C802, and a 500-kc if. filter that
V803 through contacts 7 and 9 of S801A,
consists of C804 and L802, and terminal
capacitor C809, and resistor R818. When
NOR-BB switch S801 is set to BB, the
b of plug P801, and J8 to broadband jack
audio input from the micorphone or Radio
J704-E.
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