Figure 24. Tuning unit 2, mixer and oscillator (70-220 mc), schematic diagram.

Figure 24. Tuning unit 2, mixer and oscillator (70-220 mc), schematic diagram.

39. If. Step Attenuator AT201

terminal 15 of multipin connector P201 (on

(fig. 25)

t h e rear of the tuning unit), feedthrough

c a p a c i t o r C2, a n d voltage-dropping re-

The output of either the 20-70-mc tuning

s i s t o r R7 to the coil of relay K2. With

section or the 70-220-mc tuning section is

r e l a y K2 energized, a 10-db T-pad (con-

coupled through wafer section Y of switch

s i s t i n g of resistors R3, R4, and R5) is

S201A (rear) and cable assembly W201 to

i n s e r t e d between the output of the mixer

input jack J1 on if. step attenuator AT201.

s t a g e and the input to interstage trans-

Relative steps of zero, 10 db, or 20 db of

former T205. The if. signal from the

attenuation are introduced into the circuit,

mixer has a path of continuity through the

depending on the position of the SIGNAL

m o v a b l e contact of relay K2 (energized)

ATTENUATOR DB control and switch S701,

and through the movable contact of relay

located in the main unit.

K1 (deenergized) to the 10-db T-pad. The

a. In the 0 SUBST. ONLY and 0 CW ONLY

output signal at connector J2 is, therefore,

p o s i t i o n s of SIGNAL ATTENUATOR DB

1 0 db smaller in amplitude than the cir-

s w i t c h S701, both relays K1 and K2 are

c u i t conditions present before energizing

d e e n e r g i z e d . Under this condition, the if.

relay K2.

signal at input connector J1 has a path of

c. In the 40-, 60-, and 80-db positions

continuity through the movable contact of

of SIGNAL ATTENUATOR DB switch S701,

r e l a y K2 direct to output connector J2.

the -150-volt supply line is coupled to two

Connector plug P211 and a short length of

terminals (14 and 15) of multipin connec-

coaxial cable feed the signal to the primary

tor P201 (on the tuning unit). Under this

o f transformer T205.

condition, - 1 5 0 volts dc is also applied

b. In the 20 DB position of SIGNAL AT-

through feedthrough capacitor C1 and

V o l t a g e - d r o p p i n g resistor R6 to energize

TENUATOR DB switch S701, the -150-volt

t h e coil of relay K1. With both relays

supply line has a path of continuity from