arates the tuned cathode input circuit from
(3) If. Amplifier V405. Further signal
t h e tuned plate output circuit. The tuned
g a i n and selectivity are increased
p l a t e and cathode circuits add gain and
by coupling the output of V404 to if.
s e l e c t i v i t y to the rf amplifier. The entire
amplifier V405. Its output is trans-
r f tuner, which houses the rf amplifier,
f o r m e r - c o u p l e d to the input of if.
the local oscillator, and the crystal mixer,
s t e p attenuator AT401.
is shockmounted within the tuning unit. The
e. If. Step Attenuator AT401. T h e if.
rubber pads of the shockmounts absorb vi-
attenuator is a ladder network with a
brational effects and prevent spurious
m i n i m u m insertion loss of 6-db and two
i n t e r f e r e n c e that might be introduced by
additional steps of 10-db and 20-db. Since
microphonics of the local osillator.
the 6-db loss is always in the system, the
a. Input Signal Path. The parts location
e f f e c t that is that of a three-position at-
diagram for tuning unit 3 (fig. 68) shows
tenuator with steps of 0, 10, and 20-db. The
t h a t the signal voltage from terminal A2
a m o u n t of attenuation introduced is con-
o n multipin connector P401 is coupled
trolled by the position of wafer switch S701,
t h r o u g h connector plug P402 and right-
located in the main unit. The output from if.
a n g l e adapter CP401 to the input of rf
step attenuator AT401 is fed to the input of
filter FL401. This selective frequency
t h e 42-mc if. amplifier.
f i l t e r has a bandpass characteristic which
f. If. Amplifiers V405 through V409.
c o r r e s p o n d s to the 200-400-mc frequency
If. amplifier V406 receives the output of the
r a n g e of the tuning unit. Other uhf fre-
if. step attenuator and couples the attenu-
quencies, such as television channels and
ated signal to the following three stages for
m i l i t a r y communication channels in the
further gain and selectivity. Each stage is
a d j a c e n t spectral region are effectively
tuned to 42-mc.
b l o c k e d from entering the rf amplifier
g. Cathode Follower V410. Cathode fol-
i n p u t circuit. The output of filter FL401
l o w e r V410 is used to obtain a low-im-
is applied through right-angle adapter
pedance source to feed detector and elec-
C P 4 0 2 to coaxial cable assembly W401.
t r o m e t e r assembly A401.
C o n n e c t o r plug P406, which terminates
h. Detector and Electrometer Assem-
c a b l e assembly W401, couples the signal
bly. This assembly is identical in function
to mating jack J405 at the input to the rf
a n d parts to the interchangeable detector
tuner subassembly (B, fig. 69). The signal
a n d electrometer used in tuning units 1
is fed to a tuned circuit which consists of
t h e closely coupled rf input coils, L401
s t a g e s present a high impedance to the
signal from the meter detector. Therefore,
b. Amplifier Circuit (fig. 28 and 69).
no signal loss is made in coupling the de-
The tuned cathode input circuit consists of
tected peak or average envelope voltage to
pickup loop L402, trimmer capacitor C401,
cathode follower V702 in the main unit.
and variable capacitor C402 which is
worm-gear driven by the front panel TUN-
43. RF Amplifier V401, Detailed Analysis
I N G control. Variable capacitor C402 is
(fig. 28, 68, and 69)
m e c h a n i c a l l y coupled to plate-tuning ca-
p a c i t o r C404 and to oscillator-tuning ca-
T h e signal voltage from the main unit
pacitor C413. Therefore, the amplifier
i s coupled to rf amplifier V401. A type
and the oscillator track over the complete
6 2 9 9 grounded grid triode amplifier of
frequency range. The low rf potential side
p l a n a r electrode construction is used be-
o f the cathode inlut tuned circuit is by-
c a u s e of its low-noise characteristic. The
passed by C403. The amplified rf voltage
right side of the rf tuner is separated from
in the plate is developed across the paral-
t h e left side by a grounded center parti-
lel-tuned circuit, which consists of tuning
tion (fig. 69). The amplifier tube is housed
c a p a c i t o r C404 and pickup loop L404.
w i t h i n the rf tuner (right side) which is
T r i m m e r capacitor C405 is adjusted dur-
divided into two sections (B, fig. 69) by
ing alignment to obtain a peak output signal
a grounded partition. This partition sep-