Fm Distortion Test - Wavetek 3001 Instruction Manual

METHOD
E
QUIPMEN T
PR OC EDURE
4.16 FM DISTOR TION
T
EST
ME THOD
EQU I PMEN T
T
he
m
easurement is ma de with α
m
odu lation
m eter and α fun ctio n gene
ιαιηι T he ( υιιε tιπιι generator αιιΡΠΙίε 5 an external sine
W
ave to frequency
m odulate t he instrument .
T
he system is cali brated with α 1 kHz external
strip wave at in indicated deviation 1 dB below the 0
d
B reference an the
modulation meter (III scalp (a pp roximately 90 kH z
d
eviation) . Tire ex-
ternal modulation
f
requency is varied f rom 1 kH z 2ο 50
H
r, and from
1 kH z to 25 kH z, an d
t
h e FM bandwidt h is measured as
t
he change in dB
from t h e cali brate d level.
(4) (6) (7)
1 . Set the in strumen t controls as follows'
FREQUENCY VERN I ER
CA L
Fre que n cy selector 520.000 MHz
M
OD UL ATIO N M OD E FM x10
M
OD ULATIO N FREQ ΕΧΤ
M OD UL ATIO N FΜ ;ΑΜ 0 ΚΗ 7
OUTPU T VERN I E R ι 3 dB
OUT P UT Step Attenuator
+1 ο dBm
2. Connect
t
h e equipment as shown in
F
igure 4.3 .
3.
Set the modulation meter to rea d F
M deviatio n at 520 MHz. Set the
RF input attenιι atinn 1π 20
d
R, the I F bandwidt h to '400 kH z, the meter
res p onse to f ast, t h e function switch [ο 1-FM,
t
h e m eter range switch to
300, and t h e filter
b
andwi d t h to 75 kH z.
4.
Set the f un ction generato r for α 1 kH z si ne wave output and
t
he
αττοηυοτοr controls for α 10 Vpp sine wave on
t
he oscillosco pe.
5. Adjust
t
he
M
OD UL ATIO N FM/AM slider fo r α mo dulation mete r
reading of -1 dS la pμroximately 90 kH z deviation ) .
6. Mai ntain the 10
V
ρςι exte rn al in put level during this step. Slowly
d
ec rease the fun ctio n generato r frequency
f
rom 1 kH z to 50 Hz, and
t
hen
slowly increase t he frequency to 25 kH z while observing the d8 scale on
t
h e modulation
m
ete r. Ι [
s
h ou l d read between 0 and -2 dB .
N
ote th e
m
aximu m change from
t
he -1
d
8
r
efe rence (ste p 5) to t he
n
earest 0.25
d B .
7,
R
epeat steps 4 throu gh 6 with the modulation mete r fu nction switch
set to -FM . Note .
t
he change
f
rom -1 dB r e f er ence as in step 6.
R
ecord
t
h e
la rger of the two changes in dB fi n -this step and in step 6) on li n e 44 of
the PTR .
SPE CI F ICATIO N 2% ι (10 kH z to 100 kH z deviation) at α f
requ ency of 1 kH z.
4%, (3 kH z to 10 kH z deviation) at α frequency of 1 kH z.
The meas ure ment is made with α mo du lation
m
eter and α d istortio n
analyzer whic h measures the distortion of the
d
emo dulated
F
M from
the modulation meter. Distortion
b
elow 3 kH z
d
eviation increases because
of resi dual FM n oise . T h e
d
isto rtion at 3 kH z
d
eviation is
m
easure d in an
environmen t whe
r
e
t
h e noise level <60 dB relative to 2 χ 10 ;
μ
bα r.
(2! (6)
4-14