Rf Tuner, 700-1,000 Mc, Introduction

this produces a difference fre-

taneously, the microswitch breaks the path

quency output that is coupled

of continuity to V505 from the deenergized

t h r o u g h microswitch S502 to the

r f tuner.

42-mc if. preamplifier. The

c. If. Step Attenuator AT501. If. s t e p

microswitch, housed within the 42-

attenuator AT501 is a ladder network with

mc if. preamplifier, is plunger

a minimum insertion loss of 6-db and two

additional steps of 16-db and 26-db. Since

actuated by a cam on the shaft of

F R E Q U E N C Y RANGE-MC switch

the 6-db loss is always in the system, the

S503.

effect is that of a three-position attenuator

with steps of 0, 10, and 20 db. The amount

(2) Tuner, 400-700 mc. The 400-700 -

o f attenuation introduced is controlled by

mc tuner functions identically

the position of SIGNAL ATTENUATOR DB

with the 700-1,000-mc tuner,

s w i t c h S701, located in the main unit.

except that FREQUENCY RANGE-

O u t p u t from if. step attenuator AT501 is

MC switch S503 must be set to the

fed to the input of the 42-mc if.

lower frequency band for its oper-

amplifier.

a t i o n . Rf amplifier V503, crystal

d. If. Amplifiers V508 through V511. If.

mixer CR502, and oscillator V504

amplifier V508 receives the output of the

serve the same purposes as de-

i f . step attenuator and couples the atten-

s c r i b e d in (1) above for the 700-

u a t e d signal to three additional stages.

1,000-mc tuner, with the oscil-

Each stage is tuned to a center frequency

l a t o r also tracking 42-mc above

o f 42-mc.

the incoming rf signal.

e. If'. Cathode Follower V512. If. cath-

(3) B+ switching. The B+ voltage for

ode follower V512 provides a low-imped-

t h e first rf amplifiers in either rf

a n c e source to feed the amplified signal

tuner is not disconnected when the

f r o m the final if. amplifier stage to the

tuner becomes inoperative. The

d e t e c t o r and electrometer assembly A501.

design of the type 6299 planar elec-

f. Detector and Electrometer Assembly.

tron tube does not permit operation

This assembly is identical in function and

with heater power applied and plate

p a r t s with the interchangeable detector

voltage disconnected. For this rea-

and electrometer assemblies used in tuning

s o n , both rf amplifiers V501 and

unit 1 (para 25j), tuning unit 2 (para 41),

V 5 0 3 are energized, regardless of

and tuning unit 3 (para 42h).

the position of FREQUENCY

RANGE-MC switch S503. However,

51. Rf Tuner, 700-1,000 Mc, Introduction

B + voltage is switched on to the

(fig, 34)

o p e r a t i v e oscillator and removed

f r o m the inoperative oscillator to

T h e signal voltage from the main unit

a s s u r e that only one heterodyned

is fed to coaxial switch S501, which is con-

signal can pass to the if. amplifier

t r o l l e d by the front-panel band selector.

channel.

With the band selector rotated to the 700-

b . 42-MC If. Preamplifier. T h e 4 2 - m c

1 , 0 0 0 - m c position, the signal voltage is

i f . preamplifier consists of three stages

conducted from the coaxial switch by cable

t h a t function identically with the if. pre-

assembly W502 and its connector plug P506

amplifier in tuning unit 3 (para 42d) in all

to mating jack J506 on the exterior of the

respects but one. The only difference be-

r f tuner assembly.

t w e e n the if. preamplifier in tuning units

a. Physical Description (fig. 34, 72, and

3 and 4 is the inclusion of a microswitch

7 4 ) . A combined physical-electrical dia-

a t the input to the tuning unit 4 if. pre-

g r a m of the rf tuner (fig. 34) shows that

amplifier. This microswitch creates a path

rf amplifier V501 and oscillator V502 are

o f continuity from the energized rf tuner

housed in a chassis containing four tuned

to the first stage of the preamplifier, which

c o a x i a l - t y p e cavities and two rectangular

i s cascode driver-amplifler V505; simul-

c o m p a r t m e n t s . The chassis is constructed