Residual Fm Test - Wavetek 3000 Instruction Manual

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
obtained at a full-scale reading of 100 with the modulation
meter range switch set to 10 .
5 . With the
distortion analyzer operating in level mode,
calibrate it for
a
0 dB panel-meter reading . The system is
now calibrated 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
residual AM 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 residual AM 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 may be 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 frequency deviation
is used to measure residual FM .
The test is performed at
maximum frequency and output level . The Signal Generator
is operated in an FM mode where 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 Radiometer AFM2
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 Fully Clockwise
OUTPUT step attenuator +10 dBm
PERFORMAKE TESTS
4-15