National NC-2-40D Manuel utilisateur

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tommvmtznian

A

high

performance

receiver

of

advanced

design

for

the

490

to

30000

kilocycle

range

HIGHLIGHTS...

•

490

to

30,000

kilocycle

Range

• 6

General

Coverage

Ranges

• 5

Amateur

Bands

with

Uniform

Bandspread

•

All

Ranges

Have

Definite,

Accurate

Calibration

•

Actual

Single

Dial

Control

•

Temperature

Compensation

•

Automatic

Voltage

Stabilization

•

Series

Valve

Noise

Limiter

•

New,

Flexible

Crystal

Filter

•

115

and

230

Volt,

50/60

Cycle

Operation

•

New,

Stabilized

S-

Meter

Circuit

•

Speaker

in

Matching

Cabinet

•

Phonograph

Or

High

Level

Microphone

Pick-up

Jack

National

Conapany,

Inc.

THE

NC-

2-40D

COMMUISTICATION

RECEIVER

NEI

TIIIN

I.

DEN.

IIIPTION

I-1.

General

The

NC-

2-40D

RADIO

RECEIVER

is

a

twelve

tube

superheterodyne

covering

the

continuous

frequency

range

from

490

to

30,000

kilocycles.

This

receiver

was

de-

signed

to

give

the

amateur

a

maximum

of

bandspreading,

and

combines

mechanical

bandspreading

on

all

bands

with

additional

electrical

bandspreading

of

the

10,

11,

20,

40,

and

80

meter

amateur

bands.

The

NC-

2-40D

Receiver

also

incorporates

very

stable

high

frequency

circuits, due

to

the

high

frequency

oscillator

circuit

design

developed

in

the

National

Laboratories,

which eliminates

the

exasperating

detuning

effect

of

the

R.F.

Gain

control,

and

the

even

more

undesirable

motor-

boating

or

fluttering

which

occurs

in

most

receivers

when

tuning

in

strong

high

frequency

sig-

nals.

Perhaps

the

best way

to

prove

the

exceptional

performance

of

this

type

of

circuit

is

in

the

10

meter

band

where

a

line

voltage

shift

from

100

to

120

volts

produces

less than

1000

cycles change

in

tuning.

This

is

a

variation

of

less than

.003

percent.

Frequency drift

has

been

re-

duced

to

a

minimum

through

use of

tempera-

ture

compensating

capacitors

not

only

in

the

high

frequency

oscillator

circuits,

but

in

the

R.F.

and

first

detector

circuits

as

well.

The

sensitivity

of

the

NC-

2-40D

is

particularly

high,

an

input

signal

of

only

1

microvolt providing

1

watt

of

audio

out-

put. R.F.

coupling

circuits

developed

in

the

National

Laboratories

have

made possi-

ble

the

maintenance

of

full

sensitivity

up

to

the

highest

frequencies

covered

by

the

receiver.

Moulded

polystyrene

coil

forms

are

used

in all

circuits,

both

R.F.

and

I.F.,

thus

assuring

the

freedom

from

cir-

cuit

losses

or

detuning

which might

other-

wise

be

caused

by

humidity

effects.

Vari-

able

condenser

insulators,

tube

sockets,

etc.,

are of

Isolantite.

The

chassis

of

the

NC-

2-40D

is

cadmium

plated

to

provide

positive

grounds

and

better

conductivity

as

well

as

a

neater

appearance.

Components

in

the

NC-

2-40D

are

treated

as

necessary

with

a

fungus-

resistant

varnish

for

an

added

protection

against

any

damage

which

may

re-

sult

from

humidity

or

temperature.

Each

equipment

consists

of

a

receiver

and

speaker

built

for

either

relay

rack

or

table

mounting

and

an

instruction

manual.

The

standard

NC-

2-40D

Receiver

is

de-

signed

for

operation

from

a

110/120

volt,

or

220/240

volt

50/60

cycle

power

source.

1-

2.

Circuit

The

circuit

employed

on

all

bands

con-

sists of

one

stage

of

radio

frequency

am-

plification,

a

separate

first

detector

and

stabilized

high

frequency

oscillator,

two

intermediate

frequency

stages,

an

infinite

impedance

second

detector,

a

self-

balancing

phase

inverter

and

audio

amplifier,

and

a

push-pull

audio

output

stage.

The second

detector utilizes

one

set

of

elements

of

a

dual

triode;

the

other

set

of

elements

is

utilized

for

a

series

valve

noise

limiter.

Separate

tubes

are

used

in

the

automatic

volume

control

and

beat

fre-

quency

oscillator

circuits.

The latter

is

coupled

to

the

second

detector

for

C.W.

re-

ception.

A

crystal

filter

is

connected

between

the

first

detector

and

first

I.F.

amplifier

tubes.

All

voltages

required

by

the

receiver

circuits

are

supplied

by

a

built-in

power

supply.

1-

3.

Tube

Complement

The

NC-

2-40P

is

supplied complete with

tubes

which

are

tested

in

the

receiver

at

the

time of

alignment.

The

tubes

employed

are

as

follows:

R.F.

Amplifier

6SK7

First

Detector.

6K8

H.F.

Oscillator

6J5

First

I.F.

Amplifier

6K7

Second

I.F.

Amplifier

6SK7

Second

Detector-

Limiter

6SL7GI/O

Automatic

Volume

Control

6V6

Beat

Frequency

Oscillator.

6SJ7

Amplifier &

Phase

Inverter...6SN7C1/G

Push-

Pull

Audio

Output (

2)

6V6

Rectifier

5Y3G

9

1-1.

Tuning System

The

master

tuning

capacitor

C-1 and

six

sets

of

coils

are

used

to

tune

the

490

to

30,000

kilocycle

range

of

the

receiver.

By

means

of

a

highly

developed

band

change

mechanism,

four

of

these

same

coil

sets

are

made

to

spread

the

10, 11,

20,

40,

and

80

meter

amateur

bands

uniformly

over

the

major

portion

of

the

tuning

dial (

HRO

System).

All ten

ranges

are

calibrated.

All

transformer

coils

of

the

R.F.

am-

plifier,

first

detector

and

H.F.

oscillator

stages

with

their

associated

padder

and

air-

dielectric

trimmer

capacitors

are

mounted

in

a

redesigned

rigid

aluminum

casting

which slides

the

length

of

the

chassis,

being moved

by the

MAIN

TUN-

ING

control.

The

various

coil

assemblies

are

fitted

with

heavy

contact

pins

which

engage

spring

contactors

mounted

immediate-

ly

under

the

variable

tuning

capacitor.

This

system

permits

thorough

shielding

of

each

individual

coil

while,

at

the

same

time,

the

coils

in

use

are

moved

to

the

best

position

in the

chassis,

giving

short-

est

leads

to

the

tubes

and

master

tuning

capacitor,

and

all

other

coils

are

com-

pletely

disconnected

from

the

circuit.

1-

s.

Crustal

Filter

Undoubtedly,

the

most

efficient,

flex-

ible

crystal

filter

yet

designed

is

used

in

the

NC-

2-40D

Receiver.

Six

uniform

steps

of

selectivity,

as

shown

in

Dwg.

No.

1,

and

a

variable

phasing

control

allow

the

re-

ceiver

to

be

adjusted

to

almost

any

operat-

ing

condition,

a

highly

desirable

feature

for

both

short

wave

communication

and

broadcast

reception.

The

curves

show

that

any

degree

of

selectivity

between

that

of

full

single

signal

operation

and

wide

band

broadcast

reception

is

available,

the

ratio

between

the

two

being

almost

forty

to

one.

1-

6.

Noise

Limiter

The

noise

limiter

of

the

NC-

2-40D

Re-

ceiver

is

of

the

series

valve

type

devel-

oped

in

the

National

Laboratories.

Its

ef-

fectiveness

and

superior

performance

as

compared

to

the

more

common

types

of "

si-

lencers"

were

proved

in

the

modernized

NC-

200

receivers.

A

threshold

control

on

the

front panel

permits

adjustment

of

the

level

at

which

limiting

action

starts.

THE

NC-

240D

HU:CFI\

ER

1-7.

Toi

e

(

Metro!

The

tone

control

is

used

to

vary

the

frequency

characteristic

of

the

audio

am-

plifier.

The

control

is

particularly

help-

ful

when

receiving

weak

signals through

in-

terference,

as

explained

in

Section

3.

I-

8.

Signal

Strength

Meter

A 0

to

1

milliammeter,

serving

as

a

signal

strength

meter,

is

front panel

mounted.

It is

fitted

with

a

scale

gradu-

ated

in

S-

units

from

1

to

9

and

in

db

above

S-9

from

0

to

40

db.

The

circuit,

in

which

the

meter

is

connected,

makes

possible

ac-

curate

signal

input

readings

from

below

1

microvolt

to

1,000

microvolts.

1-

9. :

1 '

sienna

Input

Antenna

input

terminals

are

located

at

the

rear

of

the

receiver

chassis

near

the

center.

The

input

circuit

is

suitable

for use

with

a

single

wire

antenna,

a

bal-

anced

feed-

line

or

a

low

impedance

concen-

tric

transmission

line.

Average

input

im-

pedance

is

500

ohms.

lo'

ice

10

OFr

-

12

10

8 6 4 2 0 2 4 6 8

tO

2

4-

2

PHASING

NOTCH

4 5

ADJUSTABLE

ON

SWITCH

POS

I 5

INCLUSIVE

KC

OFF

RESONANCE

4 3 2

OFF

MAX

SELECTIVITY

-

200

CYCLES

TOTAL

Mpg.

No.

1.

Typical

Selectivity

Characteristics

THE

W-2-101)

RECE1\

-

FR

I-

HL

Audio

Output

Two

audio

output

circuits

are

provid-

ed:

(1)

A

headphone

jack

is

mounted

on

the

front

panel

and

is

wired

so

as to

silence

the

loud-

speaker

when

the

phone

plug

is

in-

serted.

The

correct

load

impedance

for

the

headphone output

is

20,000

ohms,

this

being

the

usual

impedance

of

phones

having

a

DC

resistance

of

between

2000

and

3000

ohms.

Maximum

audio

output

available

at

the

phone

jack

is 15

milliwatts.

(2)

A

five

prong

speaker

socket (

X-1)

is

provided

at

the

rear

of

the

receiver

chassis.

To this

socket

are

brought

the

audio

output

leads.

The

proper

load impe-

dance (

total)

for

the

output

circuit

is

10,000

ohms.

Maximum

undistorted

audio

power

output

available

is

8

watts.

1-

11.

Power

Supply

The

standard

NC-

2-40D

Receiver

is

de-

signed

for

operation

from

a

110/120

volt,

or

220/240

volt

50/60

cycle

power

source.

A

toggle

switch

is

provided

in

the

dual

primary

circuit of

the

power

transformer

to

permit

operation

from

either

voltage. Nor-

mal

power

consumption

is

approximately

100

volt-

amps.

The

built-in

power

supply

de-

livers

all

voltages

required

by

the

heater

and

B

supply

circuits -

4.5

amperes

at

6.3

volts

and

100

milliamperes

at

250

volts,

respectively.

One

side

of

the

AC

input

line

is

connected

through

a 2

ampere

and

a 1

ampere

fuse

housed

in

extractor

posts

marked '

FUSE"

which

are

mounted

at

the

rear

of

the

receiver

chassis.

The

2

ampere

fuse

is

used

in

the

circuit

for

3

115

volt

operation.

Both

2

and

1

ampere

fuses

are

used

for 230

volt

operation.

All

NC-

2-40D

Receivers

are

equipped

with

a

seven

prong

plug

and

socket

combina-

tion

to

permit

portable

or

emergency

opera-

tion

from

batteries.

See

Section

2-3.

1-

12.

Loud

Speaker

The

loud-

speaker

supplied

with

the

table

model

NC-

2-40D

Receiver

is

of the

permanent

magnet

field

type

having

a

nomi-

nal

diameter

of

10

inches.

A

coupling

transformer,

mounted

on

the

loud-

speaker

chassis,

matches

the

voice

coil

to

the

out-

put

impedance

of

the

receiver.

A

shielded

three

wire

cable

and

plug

is

furnished

for

connection

between

the

loud-

speaker

and

re-

ceiver.

A

cabinet,

finished

to

match

the

re-

ceiver,

houses

the

loud-

speaker

for

table

mounting.

The

cabinet

interior

is

lined

with

sound

absorbent

material

to

avoid

any

undesirable

mechanical

resonance.

A

10

1/2

x

19

inch

panel

of

1/8

inch

steel

is

used

to

support

the

ten

inch

loud

speaker

chassis

in

a

relay rack

installa-

tion.

1-13

Pirk-up

Jae!:

A

pick-up

jack

mounted

on

the

front

panel

of

the

receiver

may

be

used

to

con-

nect

auxiliary

apparatus,

such

as

a

phono-

graph

pick-up,

to

the

audio

system

of

the

NC-

2-40D

Radio

Receiver.

This

input

cir-

cuit

is

high

impedance

and

feeds into

the

6SN7GT/G

Audio

Amplifier-

Phase

Inverter

tube.

The

TONE

and

A.F.

GAIN

controls

are

operative

with

this

connection.

SECTION

2.

INSTALLATION

2-1.

Antenna

Recommendations

%ben

using

a

single-

wire

antenna,

the

lead-in

should

be

connected

to

one antenna

input

terminal

and

the

short

flexible

lead,

which

is

attached

to

the

chassis,

should

be

fastened

to

the

other

terminal.

The dimen-

sions

of

the

single-

wire

antenna

system

are

not

critical,

the

recommended

length,

in-

cluding

lead-in,

being

from

75

to

100

feet,

although

any

length

between

25

and

200

feet

may

be

used.

Feed-

lines

of

doublet

systems

should

be

connected

to the

two

input terminals.

The

flexible

lead

is

not

used.

lhe

inner

conductor

of

a

concentric

transmission

line

should

be

connected

to

one

input

terminal.

The

outer

conductor

and

the

flexible

grounding

lead

should

be

connected

to

the

other

terminal.

An

external

ground

connection

to

the

chassis

may

or

may

not

be

necessary.

It

should

be

used

unless

it

reduces

signal

strength.

THE

NC-

2-40D

RECEIVER

ANT

GNa

his.

No.

1.

2-2.

td

Operation

Rear

hew

of

Receiver

After

unpacking

the

NC-

2-40D

Receiver

and

loud-

speaker

from

the

shipping

cases,

proceed

as

follows:

(1)

Remove

the two

coil

carriage

lock-

ing

screws

on

the

right

hand

side

of

the

cabinet

before

attempting

to

slide

the

coil

carriage.

(2)

Make

sure

tubes

are

firmly

in

their

sockets.

(3)

Insert

the

dummy

connector

plug

P-2

in

the

seven

prong

socket

X-2.

(4)

Insert

loud-

speaker

plug

P-1

in

the

five

prong

audio

output

socket

X-1

of

the

receiver.

(5)

Connect

antenna

feed

line.

(6)

Set

primary

selector

switch

for

line

voltage

to

be

used,

i.e.

115

or

230.

(7)

Plug

AC

line cord

in

proper

source

of

supply.

(8)

Set controls

as

recommended

in

Section

3

for

reception

of

signals.

2-3.

flattery

Operation

The

NC-

2-40D

may

be

operated

in

port-

able

or

emergency

service

by

connecting

batteries

to

the

terminals

of

battery

con-

nector

plug

P-3

and

inserting

it

in

socket

X-2

in

place

of

plug

P-2.

See

Fig.

No.

1.

For

normal

operation

with

somewhat

reduced

F-

I )

X-

I

BSW

P-2

F-2 \

X-2

loud-

speaker

output,

a 6

volt

heater

supply

(storage

battery)

should

be

connected

to

terminals

1

and

2

of

plug

P-3,

and

a

180

volt

B

supply

should

be

connected

to

plug.

terminals

5

and

6.

During

battery

opera-

tion

the

Bi-

and

BS» switches

are

operative.

Battery

economy

may

be

effected during

headphones

operation

by

removal

of the

speaker

plug

P-1

from

socket X-1

which

will

open

the

6V6

B

supply

without harming

the

output

tubes.

A

further

economy

of

battery

power

during

headphones

operation

may

be

accomplished

by

removal

of

the two

6V6

out-

put

tubes

from

their

sockets.

The

AC

line

switch

does

not

render

the

Receiver

in-

operative

during

battery

operation.

It

is

necessary,

therefore,

to

remove

the

battery

plug

to

effectively

disconnect

the

battery

from

the

Receiver.

Do

not

attempt

to

use

plug

P-2

for

battery

connection,

since

the

jumper

be-

tween

terminals

1

and

7

would

be incorrect.

.

The recommendations

of

Section

3,

OP-

ERATION,

apply

to

the

battery

powered

NC-

2-40D.

2-

1.

Laud

Speaker

If

the

installation

is

such

that

the

loud-

speaker

will

be

placed

close

to

the

receiver,

the

most

desirable

position

is at

the

side.

Placing

the

loud-

speaker

on

top

THE

NC-

2-40D

RECEIVER

5

of

the

receiver

is

not

desirable

since

vi-

bration

from

the

speaker

might

possibly

in-

3-

1.

Controls

troduce

microphonic

noises

which

would

not

otherwise

be

noticlable.

SFA

I

ION

3.

ILTION

The

MAIN

TUNING

control

knob

is

located

at

the

middle of

the

front

panel

and

operates

a

three-

gang variable

capaci-

tor

Gl

through

a

44

to

1

ratio

reduction

drive

mechanism.

The

main

dial has

ten

ac-

curately

calibrated

scales,

the

scale

in

use

being

definitely

indicated

by

band

mar-

kers

appearing

at

the

scale

ends.

A

dial

pointer

shows

the

frequency

to

which

the

receiver

is

tuned.

The

accuracy

of

the

general

coverage

calibration

can

be

relied

upon

to

be

better

than

plus

or

minus

1%.

Immediately

below

the

pointer

is

a

vernier

dial

which

may

be

used

to

accurately

log

incoming

signals.

The

tuning

system

of

the

NC-

2-40D

is

truly

single

control;

in

fact,

the

MAIN

TUNING

control

referred

to

above

is

used

for

band

changing

as

well

as

tuning.

To

select

either

a

general

coverage

or

bandspread

coil

range,

the

MAIN

TUNING

control

knob

is

pulled

out

about

1/4

inch.

When

this

is

done,

the

dial

and

capacitor

drive

mechanism

is

disengaged

and

the

knob

is

geared

to

the

coil

casting.

As

the

knob

is

turned,

the

coil

carriage

is

moved

across

the

chassis

until

the

proper

coil

pin

contacts

engage

the

circuit

contactors,

as

indicated

by

the

scale

markers.

Approx-

imately

one

full

turn

of

the

MAIN

TUN-

ING

knob

is

required

to

change

from

one

general

coverage

range

to an

adjacent

general

coverage

range.

Approximately

one

quarter

turn

of

the

knob

is

required

to

shift

from

a

general

coverage

range

to

the

associated

bandspread

range

near

the

high

frequency

end.

The

knob does not

turn

smoothly

between

ranges,

but

only

a

few

minutes

is

required

to

become

familiar

with

its

action.

After

the

desired

range

has

been

selected,

the

tuning

knob

is

pushed

in

to

its

original

position,

engaging

the

ca-

pacitor

drive

and

disengaging

the

coil car-

riage

rack.

The

LIMITER

control,

at

the

left-

hand

side

of

the

receiver

panel,

is

used

to

POWER

SWITCH

METER

LIMITER

CONTROL

CONTROL

SWITCH

PHONES

JACK

R F

GAIN

CONTROL

MAIN

TUNING

DIAL

'

n111.11111110118111

.1

"nnil

BAND

CHANGE

AND

TUNING

KNOB

VERNIER

DIAL

TONE

CONTROL

SELECTIVITY

CONTROL

C W

OSC

CONTROL

PICK-UP

JACK

A F

GAIN

CONTROL

Fig.

No.

2.

Front

View

of

Receiver

6

THE

NC-

2-40D

RECEIVER

adjust

the

DC

potential

applied

to

the

ele-

ments

of

the

series

valve

noise

limiter

tube.

The limiter

circuit

is

thus

provided

with

an

adjustable

threshold

at

which

lim-

iting

starts.

Any

audio

voltages,

or

peaks,

in

excess

of

this

threshold

are

pre-

vented

from

reaching

the

audio

amplifier.

With

the

LIMITER

control

set

at

0,

the

limiter

circuits

will pass

all

but

the

strongest

audio

peak

voltages;

when

the

control

is

set

at

10,

the

threshold

is

low-

ered

to

a'point

where

the

audio

signal

will

be

distorted

due

to

suppression

of

the

pos-

itive

peaks.

The

R.F.

GAIN knob

is

located

be-

low

and

to

the

right

of

the

LIMITER

knob.

It

is

used

to

adjust

the

amplifica-

tion of

the

R.F.

amplifier

and

two

I.F.

am-

plifier

tubes.

Amplification

increases

as

the

control

is

turned

clockwise

towards

10.

A

CONIBOL

SWITCH

is

mounted

above

the

R.F.

GAIN

control

knob.

In

the

AVC

position,

the

automatic

volume

con-

trol

circuits

are

in

operation

and

the

S-

meter

is

switched

on;

in

the

MVC

posi-

tion,

automatic

volume

control

and

the

S-

meter

are

turned

off;

in

the

CWO

po-

sition,

the

beat

frequency

oscillator

is

turned

on and

automatic

volume

control

and

S-

meter

are

turned

off.

The

POWER

SUPPLY

control

knob

is

directly

above

the

CONTPOL

SWITCH.

In

the

counterclockwise

position,-

OFF,

the

receiver

is

turned

off,

the

primary

circuit

being

opened

by

the

AC

line

switch;

in

the

mid-

position,

8+

OFF,

the

AC

line

switch

is

turned

on

but

the

B

supply

circuits

are

incomplete

since

the

B+

switch

is

open;

in

the

clockwise

position,

B+

ON,

the

B+

switch

is

closed,

completing

the

B

supply circuit. The

8+

OFF

position

may

thus

serve

as

a

stand-by

switch

for

rendering

the

receiver

inoperative,

as

may

be

required

during

transmission

periods.

The

PRIMARY

SELECTOR

SWITCH

of

the

power

transformer

is

mounted

on

the

re-

ceiver

chassis

to

the

right

of

the

power

transformer.

This

switch

selects

the

prop-

er

circuit

arrangement

of

the

dual

primary

for

operation

from

either

115

or

230

Volt

power

source.

There

is

a

shield

provided

to

prevent

unintentional

throwing

of

the

switch.

The

A.F.

GAIN

control

knob

is

lo-

cated

to

the

right

of

the

MAIN

TUNING

control.

It is

used

to

adjust

the

audio

amplification

of

the

receiver.

Audio

am-

plification

increases

as

the

control

is

turned

towards

10

on

the

scale.

The

PHASING

and

SELECTIVITY

knobs,

located

above

the

A.F.

GAIN

knob,

con-

trol

the

action

of

the

crystal

filter.

When

the

SELECTIVITY

control

is

set

at

OFF,

the

crystal.

is

switched

out of

the

circuit.

With

the

crystal

switched

out,

the

phasing

control

has

little

influence

on

receiver

performance.

With

the

SELEC-

TIVITY

control

knob

set

at

any

point

between

1

and

5,

inclusive,

the

crystal

filter

is

in

operation,

selectivity

in-

creasing

as

the

knob

is

advanced

to

5.

See

Fig.

No.

2.

The

PHASING

control

is

then

used

to

balance

the

crystal

bridge

circuit

and

eliminate

interfering

signals

or

heterodynes.

See

Sections

3-2

and

3-3.

The

C.W.

OSC.

control

knob

located

to

the

right

of

the

PHASING

control

is

used

for

varying

the

frequency

of

the

beat

oscillator.

At

0

on

the

C.W.

C.

scale,

the

beat

oscillator

is

tuned

to the

inter-

mediate

frequency.

See

Section

3-3.

A

TONE

control

knob

is

located

above

the

C.W.

OSC.

knob

and

is

used

to

vary

the frequency

characteristic

of

the

audio

amplifier

as

previously

described.

A

BSW

terminal

panel

is

mounted

at

the

rear of

the

receiver

chassis.

The

termi-

nals

are

connected

in

parallel

with

the

14

switch.

If

external (

remote)

stand-by

con-

trol

is

desired,

it

can

be

accomplished

by

connecting

a

switch

or

relay

to

these

ter-

minals.

3-2.

Phone

Reception

After

the

equipment

is

properly

in-

stalled,

in

accordance

with

Section

2,

it

is

placed

in

operation

by

turning

the

POWEP

SUPPLY

switch

to

B+

ON.

The

LIM-

ITER

control

should

be

set

at

0.

The

CONTROL

SWITCH

should

be

set

at

AVC.

The

PHASING

knob

should

be

set

at

0;

the

SELECTIVITY

at

OFF;

the

TONE

con-

trol

should

be

set

to

give

the

desired

audio

characteristic;

the

R.F.

GAIN

control

should

be

advanced

to

some

point

between

8

and

10,

depending

upon

receiving

conditions;

the

A.F.

GAIN

control

should

be set

at the

point

providing

the

desired

audio

volume.

The

receiver

is

now

adjusted

for

the

reception

of

phone

signals

and

will

THE

NC-

2-40D

RECEIVER

7

tune

to

the

frequency

indicated

by

the

MAIN

TUNING

dial.

The

C.W.

OSC.

knob

has

no

influence

on

receiver

performance

under

these

conditions.

With

the

CONTROL

SWITCH

set

in

the

AVC

position,

as

recommended,

the

R.F.

GAIN

knob

should

be

advanced

as

far

as

receiving

conditions

permit,

or

until back-

ground

noise

becomes

objectionably

loud.

Audio

output

should

be

adjusted

entirely

by

means

of

the

A.F.

GAIN

knob.

The

operator

must

remember

that

automatic

vol-

ume

control

action

will

be

restricted

un-

less

the

B.F.

GAIN

knob

is

fully

ad-

vanced.

The

CONTROL

SWITCH

may

be

set

at

MVC,

in

which

case

the

operator

must

be

careful

not

to

advance

the

R.F.

GAIN

knob

to

a

point

where

I.F.

or

audio

ampli-

fier

overload

occurs.

Such

overload

is

in-

dicated

by

distortion.

In

general,

the

A.F.

GAIN

control

may

be

set

about

half-

way

on,

i.e.,

at

5

and

the

audio

output

ad-

justed

by

means

of

the

B.F.

GAIN

con-

trol.

If

a

signal

is

weak

and

partially

ob-

scured

by

background

noise

and

static,

best

signal-to-noise

ratio

will be

obtained

by

turning

the

TONE

control

towards

the

LOW

position.

The most

effective

set-

ting

must

be

determined

by

trial

as

too

much

attenuation

of

high

audio

frequencies

will

impair

the

intelligibility

of

speech.

When

a

signal

is

accompanied

by

static

peaks or

noise

pulses

of high

intensity

and

short

duration,

the

best

signal-to-noise

ratio

will

be

obtained

by

advancing

the

LIMITER

control

towards

10.

The

best

setting

must

be

determined

by trial

as

too

much

limiter

action

will

impair

audio

qual-

ity.

If

static

peaks

and

noise

pulsés

are

extremely

strong

or

if

they

are

of

fairly

long

duration,

the

effectiveness

of

the

limiter

will

be

best

with

the

CONTROL

SWITCH

in

the

MVC

position.

In

such

cases

both

R.F.

GAIN

and

LIMITER

con-

trols

must

be

carefully

adjusted

for

opti-

mum

signal-to-noise

ratio.

The

selectivity

of

the

receiver

may

be

adjusted

by

means

of

the

crystal

filter.

The

normal

setting

of

the

SELECTIVITY

control

in

phone

reception

is at

one

of

the

positions

affording

broad

selectivity.

Po-

sitions

1

or

2

are

recommended.

Selectivi-

ty

may

be

progressively

increased

by

turn-

ing

the

SELECTIVITY

control

to

posi-

tions

3,

4

or

5

although

advancing

the

con-

trol

too

far

will

increase

selectivity

to

a

degree

where

phone

signals

become

unintel-

ligible.

The

PHASING

control

is

used

to

eliminate

or

attenuate

heterodynes

func-

tioning

only

when

the

SELECTIVITY

con-

trol

is

at

some

position

other

than

OFF.

The

normal

setting

of

the

PHASING

con-

trol

in

phone

reception

is

at

0

on

the

scale.

If,

after

a

signal has

been

tuned

in,

an

interfering

signal

causes

a

hetero-

dyne

or

whistle,

the

PHASING

control

should

be

adjusted

until

the

interference

is

reduced

to

a

minimum.

The

setting

of

the

PHASING

control

which

próvides

max-

imum

attenuation

of

the

heterodyne

will

de-

pend

upon

the

pitch

of

the

heterodyne

whistle.

If

the

beat note

is

above

1000

.

cycles,

the

optimum

PHASING

control

setting

will

be

near

0;

if

the

beat

note

is

300

or

400

cycles,

the

optimum

PHAS-

ING

control

setting

will

be

near

one

end of

the

scale

or the other,

depending

upon

whether

the

interfering

signal

has

a

higher

or

lower

frequency

than

the

desired

signal.

It

is

recommended

that

the

TONE

control

be

set

in

the

HIGH

position

when

using

the

crystal

filter

in

phone

re-

ception.

The

resulting

attenuation

of

low

audio

frequencies

tends

to

compensate

for

the

side-

band

cutting

action

of

the

crystal

filter.

3-3.

C.

W.

Receptions

The

initial

adjustment

of

the

receiver

for

C.W.

reception

is

as

described

in

Sec-

tion

3-2,

except

that

the

CONTROL

SWITCH

must

be

in

the

CWO

position.

The

C.W.

OSC.

control

should

be set

at

mid-

scale.

The

sensitivity

of

the

receiver

should

be

adjusted

by

means

of

the B.F.

GAIN

control,

care

being

taken

not

to

advance

the

control

to

the

point

where

strong

sig-

nals

will

cause

I.F.

or

audio

amplifier

overload,

as

indicated

by

excessive

thump-

ing.

The

action

of

the

TONE

and

LIMI-

TER

controls

will

be

similar

to

that

described

under

Section

3-2.

When

receiv-

ing

C.W.

signals,

it

will

be

possible

to

advance

both

TONE

and

LIMITER

controls

considerably

further

than

is

possible

in

8

THE

N(:2-

40D

RECEIVER

phone

reception,

since audio

distortion

is

relatively

unimportant.

Turning

the

C.

W.

OSC.

control,

which

is

a

variable

air

capacitor,

will

change

the

characteristic

pitch

of

the

re-

ceiver

background

noise.

This

control

en-

ables

the

operator

to

vary

at

will

the

au-

dio

beat

note of

any

C.W.

signal

to

a

pre-

ferred

tone.

The

pitch

will

become

higher

as

the

beat

frequency

oscillator

is

detuned

from

the

I.F.

amplifier.

With

the

C.W.

OSC.

control

set

at

2

or

3 (

on

either

side

of

0),

the

characteristic

pitch

of

the

receiver

background

noise

will

be

in

the

neighborhood

of

2000

cycles.

Under

these

conditions,

the

audio

beat

note of

any

C.W.

signal

will show

a

broad

peak

at

approxi-

mately

2000

cycles.

This

peak

will

appear

on "

one

side

of

the

carrier"

only

and

the

*

other

side,

where

the

audio

beat

note

is

around

2000

cycles,

will

be

considerably

weaker.

This

characteristic,

known

as

"semi-

single

signal",

is

helpful

in

receiv-

ing

weak

signals

through

interference.

As

stated

in

Section

3-2,

the

selec-

tivity

of

the

receiver

may

be

adjusted

by

means

of

the

crystal

filter,

the

action

of

the

SELECTIVITY

and

PHASING

controls

in

C.W.

reception

being

similar

to

that

de-

scribed.

It is

possible,

however,

to

uti-

lize

the

full

range

of

crystal

filter

se-

lectivity

in

C.W.

reception.

Maximum

se-

lectivity

is

obtained

with

the

SELEC-

TIVITY

control

set

at

5.

With

this

setting

the

single-

signal

effect,

outlined

I-

1.

Tube»

Failure.»

above,

becomes

very

pronounced;

in

other

words,

the

audio

beat

note

is

very

sharply

peaked

at

a

definite

audio

frequency

which

is

determined

by

the

setting

of

the

c.e.

OSC.

control.

The

operator

may

have

diffi-

culty

in

finding

the

audio

peak

when

first

attempting

to

use

the

crystal

filter.

Aft-

er

a

signal has

been

accurately

tuned

to

give

peak

response,

the

B.F.

GAIN

con-

trol

may

need

to

be

retarded

in

order

to

prevent

I.F.

or

audio

overloading.

With

the

receiver

tuned

to '

trystal

peak",

an

interfering

signal

may

be

attenuated

by

proper

setting

of

the

PHASING

knob

since

this

control

does

not

appreciably

affect

the

desired

signal.

3-

1.

Measurement

ol

Signal

Strength

To

make

a

measurement

of

signal

strength

by

means

of

the

S-

meter,

the

B.F.

GAIN

control

must

be

advanced

to

10,

and

the

CONTROL

SWITCH

set

at

the

AVC

position.

The

crystal

filter

should

be

turned

OFF

by

means

of

the

SELECTIVITY

control;

the

PHASING

knob

set

at

0.

The

TONE,

LIMITEB

and

A.F.

GAIN

controls

do

not

affect

the

meter

reading.

Tuning

the

receiver

to

a

signal

will

cause

the

meter

to

read,

indicating

the

signal

input

in

S-

units

or

in

decibels

above

the

S-9

level.

Measurement

of

the

signal

strength

of

C.W.

signals

cannot

be

made

with

the

beat

frequency

oscillator

in

operation.

SE1

TION

1.

SE11‘11

E

AND

TENT

DATA

Failure

of

a

vacuum

tube

in

the

re-

ceiver

may

reduce

the

sensitivity,

produce

intermittent

operation,

or

cause

the

equip-

ment

to be

completely

inoperative.

In

such

cases,

all

tubes

should

be

checked

either

in

an

analyzer

or

similar

tube

testing

equipment,

or

by

replacement

with

tubes

of

proven

quality.

All

tubes

should

be

marked

as

they

are

removed

from

the

receiver

so

that

they

may

be

returned

to

their

original

sockets

thereby

reducing

the

necessity

for

realignment.

Individual

tubes

of

the

same

type

will

vary slightly

in

their

characteristics

and

it

is

well

to

remember

this

fact

when

re-

placements

become

necessary.

Even though

the

circuit

is

designed

to

reduce

the

ef-

fect

of

such

variations

to

a

minimum,

the

high

frequency

oscillator

and

I.F.

tubes

should

be

selected with

some

care.

A

re-

placement

high

frequency

oscillator

should

be

checked

in

the

receiver

to

make

sure

that

the

inter-

electrode

capacities

are

the

same

as

those

of

the

tube

originally

em-

ployed.

This

is

easily

determined

by

not-

ing

any

change

in

dial

calibration,

partic-

ularly

in

the

amateur

bandspread

ranges.

Substitution

of

new

tubes

in

the

I.F.

amplifier

may

possibly

alter

overall

gain

and

selectivity

characteristics.

Instruc-

tions

for

realignment

are

given

in

detail

in

Section

5-2.