Fig. 18. Analysis of sync pulse distortion
FM
R E C E I V E R A D J U S T M E N T S
1. Connect a sweep generator to the mixer input of the
FM receiver. Set the sweep generator for a 10.7MHz
center sweep.
2. Connect the sweep voltage output of the sweep
generator to the CH2 input jack of the oscilloscope
and set the oscilloscope controls for external horizon-
tal sweep (SWEEP TIME/DIV to X-Y).
3. Connect the vertical input probe to the demodulator
input of the FM receiver.
4. Adjust the oscilloscope vertical and horizontal gain
controls for display similar to that shown in Fig. 20A.
5. Set the marker generator precisely to 10.7MHz. The
marker "pip" should be in the center of the bandpass.
N O R M A L
S Y N C P U L S E
S Y N C P U L S E
C O M P R E S S I O N
C A U S E D B Y
L I M I T I N G
" W H I T E "
S A T U R A T I O N
C A U S E D B Y
L I M I T I N G
6. Align the IF amplifiers according to the manufacturer's
specifications.
7. Move the probe to the demodulator output. The " S "
curve should be displayed, and the 10.7MHz "pip"
should appear in the center (see Fig. 20B).
Adjust the demodulator according to the manufac-
turer's instructions so the marker moves an equal dis-
tance from the center as the marker frequency is
amplified an equal amount from the 10.7MHz center
frequency.
Fig. 20. Typical FM receiver alignment set-up
19
Fig. 19. Sync pulse waveforms
C I R C U I T
D E F E C T
H O R I Z O N T A L
P U L S E
D I S T O R T I O N
O V E R A L L R E C E I V E R
F R E Q U E N C Y R E S P O N S E
E F F E C T ON
P I C T U R E
NORMAL
CIRCUIT
PICTURE
NORMAL
LOSS OF HIGH
FREQUENCY
RESPONSE
LOSS OF P I C -
TURE DETAIL
EXCESSIVE HIGH
FREQUENCY R E -
SPONSE, NON-
LINEAR PHASE
SHIFT
FINE VERTICAL
BLACK t WHITE
STRIATIONS FOL-
LOWING A SHARP
CHANGE IN P I C -
TURE SHADING
LOSS OF LOW
FREQUENCY
RESPONSE
CHANGE IN SHA-
DING OF LARGE
PICTURE AREAS;
SMEARED P I C -
TURE
M A R K E R
G E N E R A T O R
S W E E P
G E N E R A T O R
M A R K E R
I N P U T
R F
O U T
S W E E P
V O L T A G E
R F
M I X E R
l
-F
A M P S
D E M O D U L A T O R
A U D I O
A M P S
O S C
F M R E C E I V E R
D I R E C T
