Section II. THEORY OF MAIN UNIT

circuit within each rf tuner is a con-

detector-electrometer a s s e m b 1 y com-

ventional triode, operating in a tuned one-

p l e t e s the major subassemblies housed in

h a l f wavelength transmission line. The

this tuning unit.

heterodyne output of a silicon diode crystal

e. Section VI sets forth the distinctive

mixer is coupled to an if. preamplifier, a

features of tuning unit 4. This unit includes

t h r e e - s t e p if. attenuator, and a main if.

two separate rf tuners, each of which em-

amplifier, identical with the signal path of

p l o y s a low-noise rf amplifier triode of

p l a n a r electrode construction, operating,

t u n i n g unit 3. The detector electrometer

a s s e m b 1 y completes the components

in a tuned coaxial one-quarter wavelength

housed in this tuning unit.

transmission line. The local oscillator

Section II. THEORY OF MAIN UNIT

metering circuit to produce a meter indi-

8. Block Diagram of Main Unit

c a t i o n . Signal flow in each circuit is as

(fig. 1)

follows:

F i g u r e 1 shows a block diagram of the

a . Cathode Follower V702A. The input

five circuits which are housed in the main

to V702A is coupled from electrometer V3

u n i t . These circuits are the audio ampli-

in the tuning unit m through terminal 8 of

f i e r , the cathode follower and meter, the

main unit connector J701. The input signal

rf input and impulse generator, the signal

amplitude at V702A is the same as the in-

a t t e n u a t o r , and the power supply. For a

p u t signal amplitude at electrometer V3,

c o m p l e t e schematic diagram of the main

b e c a u s e of the extremely high-impedance

u n i t , refer to figure 98. A block diagram

characteristics of the electrometer cir-

description of these five major circuits is

cuit.

given in paragraphs 9 through 13. Circuit

b . Cathode Follower V702B. The input

description of individual stages of the main

to V702B is coupled from electrometer V4

unit is given in paragraphs 14 through 24.

i n the tuning unit through terminal 11 of

main unit connector J701. The input signal

9. Block Diagram of Audio Amplifier

amplitude at V702B is approximately one-

(fig. 1)

third of the input signal amplitude to the

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

This circuit receives its driving voltage

reduction in signal amplitude is caused by

f r o m audio detector V1 in the detector-

a voltage-divider network at the input to

e l e c t r o m e t e r assembly through terminal

A1 of main unit jack J701 and the corre-

meter detector V2. Therefore, cathode fol-

sponding terminal on the tuning unit plug.

lower V702B produces a smaller amplitude

s i g n a l than cathode follower V702A. The

The output of the audio amplifier produces

an aural signal which is monitored by con-

d i f f e r e n c e in the outputs of V702B and

n e c t i n g one or two headsets i n t o the

V702A is applied to the metering circuit.

PHONES jacks provided on the main unit

11. Block Diagram of Rf Input and

f r o n t panel.

Impulse Generator Circuits

10. Block Diagram of Cathode Followers

(fig. 1, 2, and 3)

and Metering Circuit

Since the rf input circuit and the impulse

(fig. 1)

g e n e r a t o r circuits are closely interrelated

in signal flow, this paragraph describes the

Cathode followers V702A and V702B re-

c e i v e separate input signals from the de-

effect of the front-panel calibration switch

t e c t o r and electrometer assembly within

on their circuit operation. The positioning

each tuning unit. Each section of the cathode

o f the calibration switch depends on the

f o l l o w e r reproduces its input signal and

a n t e n n a or coupler which is used at the

applies the difference in amplitude to the

input to the test set. Shunt calibration (a