CT Systems Wavetek 2500 - Page 37

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3.4.2

Sensitivity

-

12

dB SINAD

Sensitivity

measurements

should

reflect

signal

+

noise

and

distortion

if

they

ar~

to

be

truly

meaningful.

SINAD

is

a

unit

of

measure

that

is

designed

to

take

these

factors

into

account.

An

accepted

definition

of

sensitivity

is

"the

amount

of

RF

required

to

measure

12

dB SINAD

from

a

receiver

whose

bandpass

is

"challenged"

with

60%

of

the

systems

maximum

deviation.

The

RF

level

for

this

measurement

is

typically

expressed

in

uV.

SINAD

is

defined

as

the

voltage

ratio:

Signal

+

Noise

+

Distortion

Noise

+

Distortion

and

is

expressed

in

dB.

The

Model

2500

quickly

performs

SINAD

measurements

and

displays

the

results

to

the

nearest

dB.

~~Lis

allows

the

user

to

rapidly

tune

receivers

for

optimum

performance.

Causes

of

distortion

such

as

high

noise

analyzed

by

connecting

an

oscilloscope

output.

or

audio

clipping

may

be

to

the

Model

2500's

Demod

Refer

to

Figure

3-4

for

the

following

test

procedure.

1)

Connect

the

RF

input

(antenna-port)

of

the

receiver

under

test

to

the

"RF IN/OUT"

jack

on

the

Model

2500.

2)

Connect

the

"SINAD

AUDIO

IN"

jack

of

the

Model

2500

acros

,s

the

speaker

of

the

receiver.

If

the

external

speaker

jack

is

used

and

it

disconnects

the

internal

speaker,

a

load

having

the

same

impedance

must

be

substituted.

3)

Select

the

GEN

mode.

4)

Program

the

receiver

frequency

in

~1z

on

the

Model

2500

using

the

numerical

keys

followed

by

the

ENTER

key.

5)

Select

the

1 kHz

modulation

function

and

adjust

it

for

60%

of

the

receivers

maximum

deviat:i.on

using

the

1kHz

level

control.

For

example,

if

the

maximum

deviation

of

the

receiver

is

specified

as

5 kHz

then

the

test

deviation

would

be:

5 kHz X

.6

=

3000

Hz

6)

Select

the

AC

pk

volts

mode

on

the

Model

2500.

7)

Open

the

squelch

control

on

the

receiver.

8)

Adjust

the

receiver

volume

to

achieve

full

rated

audio

power,

as

specified

by

the

radio

manufacturer.

Use

the

internal

voltmeter

to

determine

audio

power

using

the

formula:

2500-MANUAL

PAGE

25

SECTION-3