Rf Tuner, 700-1,000 Mc, Dynamic Circuit Analysis

B + potential to oscillator V502.

which is anchored to the second

Feedthrough capacitor C511 pen-

p a r a l l e l 1/2-wavelength transmis-

e t r a t e s the exterior chassis wall

sion line. Pins 2 and 3 of the tube

a r e not used. The heater (pins 1

t h a t encloses the resistor R505

compartment (A, fig. 74). The B+

and 6) and the cathode (pin 7) are

voltage is reduced by R505 to the

s e c u r e d to supporting metallic

c l a m p s which prevent mechanical

p r o p e r value for tube operation.

vibration and provide secure elec-

The low-potential terminal of

trical contact to the following po-

R505 is connected to feedthrough

t e n t i a l s required for tube opera-

c a p a c i t o r C509. This capacitor

tion:

s e r v e s two functions: it pene-

trates the interior wall that sep-

(a) Heater voltage is connected from

arates the R505 compartment

t h e power supply through feed-

from the oscillator cavity; it

t h r o u g h capacitor C540, which

s i m u l t a n e o u s l y bypasses rf cur-

p e n e t r a t e s the chassis wall that

rents in the B+ supply to chassis

enc1oses

the crystal diode

ground. The B+ voltage is applied

CR501 compartment. A wire

through rf choke L508 to the plate

lead conducts the heater voltage

t o a second feedthrough capac-

(pin 4) of the oscillator tube.

itor, C558, which is inserted

t h r o u g h the common wall that

52. Rf Tuner, 700-1,000 Mc, Dynamic

separates the crystal diode com-

Circuit Analysis

p a r t m e n t from the fixed resistor

(fig. 34)

R 5 0 5 compartment (fig. 34). A

T h e rf incoming signal is applied to a

s e c o n d wire lead continues the

d o u b l e - t u n e d quarter-wavelength shorted

conduction path to the inner ter-

coaxial line type of cavity at the input to

m i n a l of feedthrough capacitor

rf amplifier V501. The signal is increased

C512, which isolates the 6.3-volt

i n magnitude by the amplifier and is fed

h e a t e r line from the grounded

to a s i n g 1 e-tuned quarter-wavelength

wall and is connected to rf choke

shorted coaxial line type of cavity in the

L 5 0 6 , which is mounted within

plate output circuit of V501. An impednace-

the oscillator cavity. Choke L506

m a t c h i n g transformer couples the plate

is connected to the heater (pin 1)

c a v i t y signal into crystal mixer CR501.

of V502. The 6.3-volt return path

A n oscillator which uses a tuned half-

is through pin 6 of V502 and rf

wavelength parallel transmission line also

choke L507 to chassis ground.

i n j e c t s its signal into the crystal mixer

(b) The bias for oscillator V502 is

i n p u t . As a result of heterodyning action

d e v e l o p e d by the voltage drop

w i t h i n the crystal mixer, sum and differ-

a c r o s s grid resistor R504. The

e n c e frequencies are produced. Since the

c a t h o d e (pin 7) has a dc return

if. preamplifier is tuned to the difference

p a t h to chassis ground through

frequency, t h i s h e t e r o d y n e d s i g n a l i s

rf choke L507.

passed on to the if. amplifiers for ampli-

(c) The B+, 105-volt dc potential is

f i c a t i o n , and to the detector and electro-

applied to the plate of the oscil-

meter circuit for metering and audio signal

l a t o r tube only when the band

detection.

s e l e c t o r is rotated to the 700-

1,000-mc position. This potential

a . V501 Input Circuit. T h e i n c o m n g

is applied through two rf chokes

signal is coupled into the first coaxial-type

a n d two feedthrough capacitors.

cathode input cavity at an area of low rf

The first choke, L522, is outside

impedance. A pickup loop is used to trans-

o f the tuner chassis and is in

f e r the rf energy from the first to the

s e r i e s with the switch terminal

second tuned cavity. Effectively, the tuned

on band selector S503 that applies

cavities function as a double-tuned rf