Section III. UHF INJECTION SUBUNIT

Section III. UHF INJECTION SUBUNIT

b. The signal applied to the grid of

17. Uhf Injection on Receive and Transmit

V201B is amplified and developed across

The uhf injection system, which consists

plate load Z201. Resistor R206 is a para-

of stages V201 through V205 (fig. 6 and 7),

sitic oscillation suppressor and C208 is a

provides 18 crystal-controlled frequencies

trimmer for Z201. Coil L222 is an addi-

that cover the 200- to 370-mc range in

tional trimmer adjustment for tuned cir-

10-mc steps. On receive, the output is

cuit Z201. The voltage developed across

heterodyned with the received rf to produce

Z201 is coupled through C210 to frequency

the first if. On transmit, the output is

tripler V202.

heterodyned with the first if. to produce

c. Resistors R203 and R204 provide

the rf carrier frequency.

cathode bias for the two triode sections of

V201. Resistor R201 and C202 provide

18. Crystal-Selection

plate decoupling for V201A. The filter

(fig. 6)

network, which consists of C239 and

a. First oscillator V201 is controlled by

FL203, decouples V201B from the +125-

1 of 15 crystals Y202, Y204, and Y206

Volt supply.

through Y218 (fig. 56). These crystals can

be selected by switch S202 to provide a

20. Multiplier Network 2201

total of 18 oscillator output frequencies

(fig. 6)

are available. Switch S201, operated with

switch S202, selects the correct plate

a. Tuned circuit Z201 is tuned to the

second harmonic of the crystal frequency

t r i m m e r coil (L201 through L218)

for V201A.

when the radio set operates in the 220.0 to

299.9-mc range. When the radio set oper-

b. Blocking capacitor C201 prevents dc

ates in the 300.0 to 399.9-mc range, Z201

plate voltage on pin 4 of V201 from being

is tuned to the third harmonic of the crystal

grounded through the coil. Rf chokes L219

frequency. Thus the frequency developed

and L220 resonate the crystal case and

across 2201 is either two or three times

socket capacities and cancel their effect

the crystal frequency, depending upon the

on the operation of the circuit.

frequency of operation selected.

19. First Oscillator V201

b. Capacitor C210 couples the output

(fig. 6)

signal from Z201 to the control grid of

a. Tube V201 functions as a cathode-

frequency tripler V202. Capacitor C208

coupled crystal oscillator. Triode section

and coil L222 are variable and insure pro-

V201A is connected as a grounded grid

per tracking for Z201.

amplifier. (Parasitic suppressor R202 ef-

fectively grounds the control grid.) The

21. Frequency Tripler V202

selected crystal in the cathode circuit of

(fig. 6)

V201A controls plate current though this

a. Frequency tripler V202 is a tuned rf

tube section. The signal voltage is devel-

voltage amplifier. Resistors R207 and

oped across plate load L221 which is

R208 and capacitor C210 are the grid leak

shunted by the selected coil (L201 through

bias circuit. Capacitor C211 bypasses rf

L218) and temperature-compensating ca-

signals to ground to prevent rf from inter-

pacitor C236. The voltage across L221 is

fering with dc bias measurements at test

coupled through C207, developed across

jack J201. Screen grid voltage is supplied

grid resistor R205, and applied to the con-

to V202 through plate voltage dropping re-

trol grid of V201B. To sustain oscillation,

sistor R213 and screen voltage dropping

feedback current is coupled from the cath-

resistor R209. Capacitor C212 provides

ode of V201B through C203; through the

the screen grid with rf ground.

selected crystal, which functions as a

b. Plate voltage for V202 is supplied

series-tuned resonant circuit; and through

through resistor R213 and rf choke L224.

C204 to the cathode of V201A.