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4. PRINCIPLES OF OPERATION

4.1

LOOP AM

PLIFIER

On Bands A and B , Q1 amplifies signals from the loop antenna and feeds

one

gate of the R.F. amplifier Q4, through C52 and the tuned circuits

formed by

C9,

Cl0,

C13,

C16, C18, C22, C23, C25, C27, C33, T2,

and T4.

On Bands A and B, signals from an external antenna connected to

(AA)

bypass

Q1 through Cl0 and Cl3 into the tuned circuits described above.

4.2 R.F. AMPLIFIER

On Bands C through H signals from an external antenna connected to

(ANT ) are coupled to Q4 through T3 and C52..T3 is resonated with C101

and the capacitors connected to S5R. Q4 is protected from large signals

by CR2 and CR3 which are reverse biased.CR2 and CR3 limit the signal

to a

safe

level

by conducting when a large signal overcomes their reverse

bias .

On Bands A and B the drain of

is untuned and drivès the 1st mixer

through C90 and C96. On Bands C through

H , the drain of Q4 is tuned by

T5, the capacitors connected to

S9F,

and drives the 1st mixer through

C90.

4.3

FIRST MIXER

The 1st mixer is a balanced mixer

comprised

of Q7 and Q8 and driven by

the R

.F . amplifier and the pre-mixer .On Band A, the pre-mixer is

by-

passed and the 1st mixer is driven from the P

.T.O.

through R25 and

C99.

On Bands B through H, the pre-mixer drives the 1st mixer through T6 and

C99.

The 1st mixer is balanced by R40 and the output is tuned by Cl02 and T8

and drives the 2nd mixer through

C110,

the 5645 crystal

filter,

and

T9.

Heterodyning of the R.F. amplifier and pre-mixer

(P.T.O.

on Band A)

results in a

difference

frequency output from

Q7/Q8

of 5645 kHz.

4.4

PREMIXER

The premixer system

consists

of the P .T

.O.

, the crystal oscillator

Q2,

the premixer transistor QS, and the tuned circuits associated with S1,

S4F,

S4R,

S8F,

and S8R.

The

collector

of the crystal oscillator

is tuned by

and the

compo-

nents connected to S1.

The feedback winding on L5 is connected

through S2 to the proper range

ctystal

and the output of Q2 is connected

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1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 65 66

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