Rf Tuner, Analysis of 20-70-Mc Amplifiers

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-

Amplifiers

ing rf signal.

(fig. 21)

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