DRAKE SPR-4 Especificaciones descargar pdf (Pagina 18)

4.9

AVC SYSTEM

The AVC threshold is established by the setting of R111, the R.F. gain

control.

R111 is normally operated fully clockwise . This applies

approx-

imately +2 volts to the AVC line through R104, R100 and CR15 with no

received signal.

Signals from T16 drive Q25 into base current on the pos-

itive R

. driving cycle which pulls the

collector

negative because the

emitter

is returned to the

5 volt

line.

The negative potential on the

col-

lector of Q25 is applied to the AVC line through CR18 and to C 171

through CR17.

The rate that

C162

charged

determines the AVC attack

time.

The AVC release time is determined by the rate that C 171

dis-

charges through

R100

allowing Cl62 to discharge through

CR15.

The

at-

tack and release times for Q4 are lengthened by R22 and C70 to eliminate

undesirable transients.

Large signals are kept from overloading

Q4 by the application of a posi-

tive voltage on Pin 3, the signal

gate.

This voltage is derived from the

S-meter

and Q-18 and the delaying circuit of CR10, R47, R52, and

C180.

On AM , S 14R shorts

out

CR10

to obtain a symmetrical attack and release

response.

4.9.1 MUTING

Muting is accomplished by placing an

open

circuit at J9 which removes

base current from Q26, lowering its

collector

voltage to -5 volts. The

cathode of CR16

will

also be at -5 volts causing it to

conduct,

applying

cut-off voltage on the AVC line which turns off Q4, Q10, Q23, and Q24

and mutes the receiver.

4.10

-METER

The

S-meter

is a voltmeter that measures the AVC voltage and is

calibrat-

ed in

”

units .

The source follower Q14, is connected to the AVC line

and drives IC- 1 which is a differential amplifier that operates the

S-

meter.

The zero adjustment is

affected

by R64 and the S-meter full

scale

sensitivity is set by R73.

16 -

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 65 66

Comentarios a estos manuales

Sin comentarios

DRAKE SPR-4 Especificaciones Pagina 18

Comentarios a estos manuales

Relacionado con productos y manuales para Receptor DRAKE SPR-4