Wavetek 132 Especificações descarregar pdf (Página 70)

f)

Viewing

the

AM

signal

(channel

B)

on

the

spectrum

analyzer,

adjust

the

variable

attenuation

on

the

carrier

(Wavetek

186)

until

the

carrier

is

suppressed.

View

the

signal

on

the

oscilloscope.

Notice

the

phase

reversals

at

the

zero

crossings

of

the

message

signal.

If

necessary,

turn

down

the

frequency

to

view

this,

but

return

it

to

1

kHz

when

complete.

This

is

a

double

sideband

suppressed

carrier

(DSBSC)

signal.

Look

at

the

detected

message.

Q:

You

will

have

to

adjust

the

plot

scale

for

the

detected

signal

(channel

C),

why?

Plot

the

message,

carrier

and

detected

message.

Q:

At

what

modulation

index

does

DSBSC

occur?

Q:

What

is

the

time

and

frequency

representations

of

the

DSBSC

signal?

Q:

What

is

the

average

power?

Q:

If

the

output

of

the

envelope

detector

was

passed

through

a

BPF

centered

at

21

kHz,

what

type

of

output

would

we

see?

Sketch

the

output.

What

would

the

frequency

representation

be?

What

would

the

power

be?

Change

the

input

to

a

square

wave

just

for

fan.

Part

2:

AM

Transmission

and

Detection

a)

Turn

on

the

power

to

the

HP8656B

signal

generator.

On

the

center,

bottom

row,

press

RF

OFF

until

the

far

right

display

is

blank

indicating

zero

transmission.

Change

the

output

of

the

Wavetek

132

to

a

500

Hz,

2

V

pp

sine

wave

(set

attenuation

at

zero).

Verify

this

on

the

oscilloscope

channel

A.

Disconnect

the

connection

to

channel

A

and

apply

it

to

your

bread

board.

Connect

it

between

a

vacant

row

and

ground.

Connect

the

negative

side

of

the

speaker

to

ground

and

the

positive

side

to

the

same

row

as

the

sine

wave.

Check

the

polarities

on

the

back

of

the

speaker.

The

wire

colors

do

not

necessarily

indicate

polarity.

Listen

to

the

tone.

Move

the

positive

lead

of

the

speaker

to

the

output

of

the

envelope

detector.

Q:

How

do

the

tones

differ?

What

does

this

tell

you

about

the

quality

of

this

detector?

Lab

3

Page

5

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