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of the subassembly to the loss produced
t h e incoming rf signal which is
by energizing the 20-db attenuation line.)
coupled from the main unit through
T h e output of the if. step attenuator is
c o n n e c t o r plug P202 and mating
coupled to the first if. amplifier.
jack J201. The amplified rf signal
c. If. Amplifier 10.7-Mc. T h i s c i r c u i t
is then applied to second rf ampli-
includes the first through fourth if. ampli-
fier V202 for further amplification.
fiers, V207 through V210, and if. cathode
T w o signals are coupled to mixer
f o l l o w e r V211. The four amplifier stages
V203A; one is the amplified rf out-
p r o v i d e additional signal gain and selec-
put of V202, the second is the output
tivity. Each stage is tuned to the 10.7-mc
of oscillator V203B. The oscillator
o u t p u t signal from the mixer stage. The
generates a signal that tracks 10.7
o u t p u t of the last if. amplifier stage is
m c higher than the incoming rf
coupled to an if. cathode follower, V211,
s i g n a l . The mixed stage hetero-
which improves the pulse response by
d y n e s the rf incoming signal with
functioning as a low-impedance source for
the oscillator signal; this produces
d r i v i n g the meter signal detector.
a difference frequency (10.7 mc)
d. Detector and Electrometer Assembly
output that is coupled through sec-
A 2 0 1 . The detector and electrometer as-
tion A of band selector S201 to the
sembly, A201 is identical with, and com-
i f . step attenuator.
p l e t e l y interchangeable with, the detector
(2) 70-220-mc section. T h e 7 0 - 2 2 0 -
a n d electrometer assembly used in tuning
m c section functions identically
u n i t 1 (para 25j). It performs the same
w i t h the 20-70-mc section, except
functions in each of the four tuning units,
t h a t selector S201 must be set to
and delivers both an audio output (to the
t h e higher frequency band for its
audio amplifier in the main unit) and a dc
operation. First and second rf am-
output (to the metering circuit in the main
plifiers V204 and V205, mixer
unit).
V206A, and oscillator V206B serve
t h e same purpose as described in
(1) above, with the oscillator also
35. Rf Tuner, Analysis of 20-70-Mc
tracking 10.7 mc above the incom-
ing rf signal.
b. If. Step Attenuator AT201. T h e i f .
W i t h the band selector rotated to the
step attenuator is a ladder network which,
20-70 mc position, a path of continuity is
s i m i l a r to the step attenuator in tuning
p r o v i d e d from switch S201B, terminal 1,
u n i t 1 (para 25f), provides an inherent
to matching transformer T201. The signal
6 - d b loss in the signal path before the
v o l t a g e is amplified by first rf amplifier
s i g n a l enters the if, amplifier. Two ad-
V 2 0 1 and is coupled to second amplifier
ditional steps of attenuation (each 10 db)
V202. Tuned circuits in the grid and plate
are inserted when SIGNAL ATTENUATOR
add gain and selectivity to the stage.
DB switch S701 (in the main unit) is ro-
a . First Rf Amplifier V201. The signal
tated to its last four clockwise positions.
voltage from band selector S201 is coupled
With S701 rotated to its 20 DB front-panel
t o the primary winding of rf transformer
s e t t i n g , the 10-db attenuation line is en-
T201. Capacitor C201, in parallel with the
ergized and the incoming signal is reduced
primary of T201, maintains the input volt-
in amplitude by 16 db. (This total loss is
age standing wave ratio at a low value and
obtained by adding the 6-db inherent loss
makes the input circuit appear as a 50-ohm
of the subassembly to the loss produced by
l o a d . The transformer T201 secondary is
energizing the 10-db attenuation line.) With
directly connected to the tuned grid circuit
S701 rotated to its 40, 60, or 80 db posi-
of V201. The tuned grid circuit consists of
tion, the 20-db attenuation line is energized
inductor L201A, capacitor C202, coil L202,
and the incoming signal is reduced in
and trimmer capacitor C203. Cathode bias
a m p l i t u d e by 26 db. (This total loss is
i s provided by the voltage drop across
obtained by adding the 6-db inherent loss
48


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