CT Systems Wavetek 2500 - Page 35

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APPLICATION NOlES

SECTION 1

RECEIVER

MEASUREMENTS

3.4.1

Receiver

Audio

Distortion

Measurement

An

important

factor

in

proper

receiver

alignment

is

knowing

the

distortion

of

the

processed

recovered

audio.

If

problems

exist

in

the

audio

circuits

causing

high

distortion,

the

12

dB SINAD

test

will

not

be

valid

since

SINAD

combines

the

distortion

factor

with

signal

and

noise

in

determining

sensitivity.

NOTE:

For

%

distortion

lower

than

1%,

it

is

best

to

use

a

lab

quality

audio

distortion

analyzer

with

greater

resolution.

Refer

to

Figure

3-3

for

the

following

test

procedure.

1>

Cable

the

antenna

port

of

the

receiver

under

test

to

the

"RF

IN/OUT"

port

of

the

Model

2500.

2)

Cable

Audio

output

or

speaker

terminals

of

receiver

to

SINAD

"AUDIO/IN".

3)

Select

GEN

mode.

4)

Select

1 kHz

and

adjust

1 kHz

level

control

for

60%

of

max

deviation,

i.e.,

3000kHz

if

max

allowable

is

5kHz.

5)

Select

VOLTS

mode.

6)

Adjust

RF

level

control(s)

to

fully

quiet

receiver

( 1

mV>.

7)

Adjust

receiver

volume

to

full

rated

audio

power,

using

Volt-meter

Feature,

and

the

formula:

v

Audio

Power

=

-----------

2r

spk

where

V =

speaker

voltage

and

r

spk

=

speaker

impedance

8)

Press

SINAD

once

or

twice

(as

required)

to

obtain

a

direct

readout

of

distortion

in

%.

NOTE:

the

SINAD

button

toggles

between

dB

and

%

expressions

each

time

it

is

pressed.

2500-MANUAL

PAGE

23

SECTION-3