3.6 Video
3.6.1 Sensibility and Signal /Noise Rate
a) Adjust the TV to a “PP” condition.
b) Apply to the antenna input a 60dBµV signal with 60% AM modulation, 1kHz
sine wave (frequency and channel factory defined).
c) Connect at the output video detector an AC voltmeter and read the voltage
V
AC.
d) Turn off the AM modulation and read the noise level “Vr” (AC voltmeter)
.
e) Calculate the signal-noise rate as following:
S/N=20 log (V
AC
/ V
R
).
f) Reduce the output level signal generator till the rate S/N reach 20 dB. In
this condition the output level signal generator is the sensibility in dBuV.
Minimum Nominal Maximum Unit
Sensibility - 37,00 46,00 dBµV
S/N 40,00 50,00 - dB
3.6.2 AGC circuit
a) Apply to the antenna input a 60dBµV signal with 88% AM modulation with
“WHITE” pattern (frequency and channel factory defined), and FM sine
wave 400 Hz audio modulation +-25 kHz deviation.
b) Adjust the TV to “PP” condition.
c) Read the DC voltage at the tuner AGC terminal. Utilize a DC electronic
voltmeter with minimum 10 MΩ impedance.
Minimum Nominal Maximum Unit
3,00 4,00 5,00 V
DC
3.6.3 AFT circuit
a) Apply to the antenna input a 60dBµV signal with 88% AM modulation with
PAL-M COLOR BAR pattern (frequency and channel factory defined), and
FM sine wave 400 Hz audio modulation +-25 kHz deviation.
b) Connect a oscilloscope in the output video detector and read the peak to
peak burst level signal “Vb”.
c) Increment the generator frequency by 500 kHz and read the new value
peak to peak burst signal “Vh” and calculate the percentage as following:
E
H
= V
H
/V
B
d) Decrement the generator frequency by 500 kHz and repeat the
procedure(c) reading the peak-to-peak burst signal V
L
and calculate the
percentage as following:
E
L
= V
L
/V
B
To Next Page
Loading...
