If. Output Selector

a. Meter Detector V2A. The if. signal

.amplifier (para 29), also consists of four

f r o m the if. output selector (para 31) is

t u n e d pentode amplifier stages in tandem

coupled to the plate of meter detector V2A

to provide a high degree of selectivity and

( p i n 6) through capacitor C7. Capacitor

a m p l i f i c a t i o n . B + voltages for the tube

C7 charges through V2A when the positive

p l a t e s and screens are provided through

portion of the input signal is applied to the

d r o p p i n g resistor R25 only when MEGA-

meter detector. During the negative portion

CYCLES band switch S1 (rear section) is

of the input signal, C7 discharges through

rotated to band 2, 4, 5, or 6. In the other

R7 and causes the peak level of the input

p o s i t i o n s , the switch cuts off these volt-

signal to be developed across R7 (negative

ages, which leaves the entire 1,600-kc if.

in respect to ground).

a m p l i f i e r inoperative.

b. Meter Detector V2B. A p p r o x i m a t e l y

two-thirds of the incoming if. signal am-

31. If. Output Selector

p l i t u d e is coupled to the plate of meter

(fig. 18)

d e t e c t o r V2B through capacitor C11. The

The if. output selector selects the output

signal voltage is reduced to two-thirds of

o f either the 1,600-kc or the 455-kc if.

its original amplitude because of the volt-

s e c t i o n and couples it direct to the de-

age divider action of connecting one paral-

t e c t o r and electrometer assembly. Con-

lel network (resistor R5 and 10-uuf capac-

n e c t o r plug P6 and mating jack J5 apply

i t o r C8) in series with a second parallel

t h e output of the 455-kc if. amplifier to

n e t w o r k (resistor R6 and 5-uuf capacitor

the selector; connector plug P5 and mating

C 9 ) . Since the output signal from meter

jack J4 apply the output of the 1,600-kc if.

d e t e c t o r V2B has the same amplitude as

a m p l i f i e r to the selector. This selector

that of its input signal, two-thirds of the

s u b a s s e m b l y consists of a relay-operated

original if. input signal (from the if. am-

s w i t c h and a decoupling network. Relay

p l i f i e r ) is present across detector load

K6 is energized from the +150-volt source

resistor R8 (negative with respect to

when the MEGACYCLES band switch S1 is

ground). In the heater circuit, C22 and C23

rotated to band 1 or 3. This action positions

bypass residual if. signals to ground.

the relay movable contact so that the output

c. Electrometers V3 and V4, Dynamic

o f the 455-kc if. amplifier has a path of

C o n d i t i o n s . The voltage developed across

continuity, through connector plug P7, to

V 2 A load resistor R7 is coupled through

the input (J1) of the detector and electro-

r e s i s t o r R12 to the grid of electrometer

meter assembly. Ressistor R61 and capac-

V3. Likewise, the signal developed across

i t o r C127 constitute the relay decoupling

V 2 B load resistor R8 is coupled through

network. Feedthrough capacitor C128 func-

r e s i s t o r R13 to the grid of electrometer

tions as an rf bypass.

V4.

(1) In the CW PEAK and PULSE PEAK

32. Meter Detector and Electrometer

positions of the function switch (on

Circuit, Detailed Analysis

t h e main unit), thermal relays Kl

(fig. 19)

and K2 are open. Each half of the

m e t e r detector dual diode has an

B e c a u s e it is difficult to obtain meter

resistance-capacitance

identical

indications that show the true peak values

time-constant circuit. For V2A,

of pulses (especially at low-repetition

the time constant is determined by

r a t e s ) , the detector and electrometer cir-

the values of coupling capacitor C7

cuit has been especially designed to detect

and 20,000-megohm load resistor

these voltages. This circuit presents a very

R 7 . For V2B, an identical value

high impedance to the incoming if. signal.

t i m e - c o n s t a n t circuit is obtained

T h e current drawn is so small that the

by C11 and R8. Capacitors C7 and

output peak (or average) voltage detected

C11 charge very fast and discharge

i s identical in magnitude with the input

very slowly, so that the peak values

peak (or average) signal. The circuit

action is as follows:

of the incoming signal are detected