Wavetek 3000 - Residual FM Test

4.9 RESIDUAL FM TEST
4 . :

Adjust the Signal Generator MODULATION
FM/AM
control
for
a modulation meter reading of 10% AM .

NOTE :

10% AM is
obtainedat
a full-scale reading of 100 with the modulation
meterrange switch set to 10 .
5 . With the
distortion analyzer operating in levelmode,
calibrate it for a 0 dB panel-meterreading . The system is
nowcalibrated at a reference level 20 dB below the carrier .
Since the modulating signal
and carrier amplitudes are equal
at 100% AM, it follows that at 10% AM the
modulating signal
is 20 dB below the carrier .
6 .

Set the Signal Generator MODULATION MODE
switch

to
"EXT" .
7 . Without
disturbing the Signal Generator and modulation
meter controls, set the distortion analyzer to read residual
AM .

Set the
range switch so that the panel meter reads
between 0 and -10 dB .

First, read the
residualAM
below
the 0 dB reference level in step 5 .

Then add 20 dB to the
above reading to obtain the
residual AM below the carrier .
(For
example, a 48 dB residualAM below the 0 dB reference
+20
dB =
68 dB residual
AM below the carrier .) The residual
AM should be >65 dB below the
carrier . Record the residual
AM in dB below the
carrier
on
line
25
of the PTR .
As many
other carrier frequencies maybe tested as desired
.
SPECIFICATION

<200
Hz in a
50
Hz to
15
kHz post-detection bandwidth . (Typ
100 Hz .) <100 Hz in a 300 Hz to 3 kHz post-detection
band-
width . (Typ 50 Hz .)
METHOD

A modulation-meter which is set to read frequencydeviation
is used to measureresidual FM .

The test is
performed
at
maximumfrequency and output level .

The Signal Generator
is operated in an FM modewhere the .residual FM is greatest .
The residual FM is measured in an environment where
the
noise
level <60 dB relative to 2x10 -4 pbar .
EQUIPMENT
Modulation Meter

RadiometerAFM2
PROCEDURE

1 . Set the Signal Generator controls as follows :
FREQUENCY selector

520 .000 MHz
MODULATION MODE

FMx100
MODULATION FREQ

EXT
MODULATION FM/AM

0
kHz
OUTPUT VERNIER

FullyClockwise
OUTPUT step
attenuator

+10 dBm
PERFORMAKE TESTS
4-15