DRAKE SPR-4 Spezifikationen PDF herunterladen (Seite 27)

puls e. Between noise pulses

full receiver gain is restored . Receiver

AVC is

affected

only by the desired signal and not by noise when the

5-NB is in use.

The 5-NB is most effective on strong, periodic impulse

noise such as ignition noise.

6.2.2 INSTALLATION

O install the 5-NB, remove the top row of three screws on each

side

the SPR-4 Receiver cabinet.

Disconnect the power

cord,

the internal

speaker

cable

and remove the cabinet top. Unplug the jumper

cable

from

the two sockets near the power transformer and marked noise blanker

.Re-

tain the jumper

cable

SO that it

may

be used if the S-NB should ever

require service.

Install the 5-NB by plugging

into the two sockets on

top of the SPR-4

chassis..

Be sure that the 5-NB is seated in the sockets

and do not disturb

any

components on the 5-NB circuit board. Replace

the cabinet top, power

cord , and speaker

cable

6.2.3 OPERATION

The 5-NB is controlled by the SPR-4 accessory switch. When the

acces-

sory switch is in NB position, the 5-NB is turned on. The accessory

switch

may

be left in the NB position for full time protection against

noise

interference

Some distortion

may

be noted when using the 5-NB on

extremely strong signals .

6.2.4 CIRCUIT DESCRIPTION

Signals at the I .F . frequency from the 1st mixer in the SPR-4 pass

through the two pole

crystal

filter

in the 5-NB and are amplified by

Q4.

The signal on the

collector

of Q4 is coupled to

and Q 10 through T2

C27, T3 and C33 where it is amplified further and passes through T4 to

the

series

gate

CRl

, CR2 and into the SPR-4 I .F . through T5 .

The I

signal on the

emitter

of Q4 is coupled through C 16 to

which drives

the balanced mixer,

and Q6.

The balanced mixer subtracts the I.

F .

signal from the

crystal

oscillator Q3 and the

difference

frequency is

cou-

pled to Q7 through T7 and C23.

Transistors Q7 and Q8 amplify the mixer

output

The

collector

of Q8 drives the pulse detector, Q 15 and the AGC

amplifiers, Qll, Q13 and

Q14.

Q14 drives Q2 and Q16 which control

the gain of Q1 and Q7 respectively .

The AGC system maintains the am-

plitude of the signals at the

collector

of Q8 SO that the pulse detector,

Q15, remains tut-off for normal radio communication signals . When

transistor Q15 is cut-off,

Q12

conducts and applies a positive potential

to the

center

tap of the secondary winding of T4 which is greater than the

+ 1 volt applied ,to the

center

tap of

primary maintaining the

series

gate in the

"on"

state .

With the series gate “on”, radio signals pass

through the 5-NB unaffected.

Noise impulses larger than the average

communication signal

will

turn on

Q15

for the

duration

of the impulse .

This turns off Q12 for the

same

duration

causing the series gate to be

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1 2 ... 22 23 24 25 26 27 28 29 30 31 32 ... 65 66

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