BE-3110
25
4.7 Adjusting the Modulation Rate
and Modulation Distortion of the
IFa Key (Refer to Fig. 4-11 adjust-
ment waveform diagram 1)
Note 9 :
Be sure to adjust according to the following order.
1. Connect the devices as shown in Connection Diagram 6.
2. Set the devices as follows.
¶
Audio analyzer
1 kHz
¶
CATV terminal
US-7ch/10 dBmV input
¶
TV modulator
Fa: Adjust to ± 25 kHz
Fv: Modulation rate 87.5%
IFa: 41.25 MHz/45 dBmV
IFv: 45.75 MHz/50 dBmV
¶
Variable resistance attenuator
Adjust the output level to 10 dBmV
¶
Video SG
Staircase wave
¶
BE-3110
Clear mode (Digitally SW: 0)
¶
CW generator
100.15 MHz/60 dBmV/75
Ω
3. Observe the S/N ratio using the audio analyzer.
4. Adjust the trimmer capacitor TC3 (CV3) of the RF ASSY so
that the value in step 3 becomes optimum.
5. Connect the devices as shown in Connection Diagram 7, and
set the devices as follows.
¶
Spectrum analyzer
0.2 dB/div
VBW: 1 MHz/RBW: 1 MHz
SPAN: 1 MHz
SWEEP TIME: 200 ms
f
0
: TV modulator Fa output
frequency
¶
Variable resistance attenuator
5.5 dB
6. Disconnect the cables connected to IFv in and IFv out of the
unit.
7. Adjust the spectrum analyzer so that the key modulation peak
level can be seen clearly on the spectrum analyzer screen. Do
not modulate the audio FM. (Use this item as the reference level.)
8. Set the variable resistance attenuator to 0 dB.
9. Adjust control VR5 (RV5) of the RF ASSY so that the bottom
level in the key modulation of the signal comes to the position
set in step 7.
10. Repeat the adjustment in steps 1 to 9 three times to raise the
accuracy.
Fig. 4-9 Connection Diagram 6
BTSC audio
multiplexing
modulator
AUDIO
analyzer
115K
TV modulator
BE-3110
TV
demodulator
VHF
AMP
CATV
terminal
Video
SG
Audio out
Video in
Staircase wave
RF out
MONITOR
MIXER
IF in
US-7ch
US-3ch
out
70dBmV
100.15
MHz
H-SYNC
TRG.
Video out
IFa in
IFa out
IFv in
IFv out
Video in
IFa out
IFa in
IFv out
IFv in
TV
IF
MOD
RF
CONV.
38.9MHz
CW
generator
in
Comp in
L out
L in
Input
Output
Comp out
Audio in
Variable
resistance
attenuator
BTSC audio
multiplexing
demodulator
Oscilloscope
