| Exciter for TV
Transmitter |
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| |
| Model No.: TW/TV/EXCITER |
| |
| The exciter consists of
following modules namely: |
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-
 Video Input Processor
- DP Corrector
- IF Carrier Generator
- Vision Modulator
- IF Combiner and Corrector
- Audio Processor
- Aural Modulator
- Local Oscillator
- IF-Channel Converter
- Analog monitoring card
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| Individual functional block
description is as follows: |
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|
VIDEO INPUT PROCESSOR
The module accepts CCIR video signal as
input. It has a loop through facility for
connecting the same signal to other input.
The unit processes the signal and outputs
fore further processing. The unit operates
on ±12V supply.
DP CORRECTOR
This module is intended to correct the
differential phase of the overall system of
Transmitter. The corrections are done at
video level. It also provides RCVR (receiver
group delay correction) required during
transmission.
IF CARRIER GENERATOR
This module generates the required vision IF
frequency i.e., 38.9 MHz. This IF carrier is
processed to give the required ICPM
correction of the overall Transmitter
system. It also generates reference pulses 5
KHz for the phase comparison for generation
of Aural IF carrier.
VISION MODULATOR
This module generates the modulated vision
IF carrier in accordance with the CCIR B
standard.
IF COMBINER AND CORRECTOR
It combines vision IF and the composite IF
signal is amplified for +3 dBm output from
the module. The other function of this
module is to correct the non-linearity
introduced by the power amplifiers.
Correction is done by changing signal
amplitude or bias to non-linear amplifier.
AUDIO PROCESSOR
This module accepts balanced audio signal
and processes the same for required
pre-emphasis. The pre-emphasis is switch
selectable from the font panel.
AURAL MODULATOR
This module provides frequency modulation
and generates FM carrier locked to vision IF
carrier. The output is 0 dBm and has an ALC
circuit for constant output. Frequency
deviation is indicated on a meter provided
on the front panel.
LOCAL OSCILLATOR
A synthesizer is used to generate local
oscillator frequencies for converting IF
signal to desired RF channel frequency in
band IV. The frequency is programmed through
DIP switches. Frequency offsets for dot,
plus and minus channel frequency can also be
programmed.
UP CONVERTER
The composite IF signal is up-converted to
channel dependent RF signal using
synthesized local oscillator signal from LO
module. Variable attenuator has been
provided to adjust the module gain for +10
dBm RF output. Provision exists in the
module for detection of RF output to use the
DC voltage so obtained for RF level
measurement for ASU. |
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| TECHNICAL SPECIFICATION OF THE EXCITER
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| 1 |
TV STANDARD |
CCIR B/G PAL 625 |
| 2 |
FREQUENCY |
470 – 860 MHz (BAND-IV/V)
{channel selected according to site requirement} |
| 3 |
MODULATION |
| 3.1 |
Vision |
NEGATIVE AM C3F |
| 3.2 |
Aural |
FM F3E |
| 3.3 |
Colour |
PAL B |
| 4 |
VIDEO INPUT |
| 4.1 |
Level |
0.5V TO 1.5V p-p / 75 OHMS. |
| 4.2 |
Return Loss |
-30 dB OR Better (0 TO 5 MHz) |
| 5 |
CARRIER FREQUENCY |
| 5.1 |
Vision Carrier |
Channel Frequency ±150 Hz |
| 5.2 |
Aural Carrier |
Channel Frequency ±150 Hz |
| 6 |
IF FREQUENCY |
| 6.1 |
Vision IF |
38.9 MHz ± 40 Hz. |
| 6.2 |
Aural IF |
33.4 MHz ± 40 Hz. |
| 7 |
OUTPUT |
| 7.1 |
Level |
0 TO +10dBm |
| 7.2 |
Aural to Vision Ratio |
1 : 10 dB. |
| 8 |
INTER-MODULATION DISTORTION |
-60 dBc OR Better |
| 9 |
SPURIOUS |
| |
-5.5 MHz |
-55 dBc OR Better |
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+11 MHz |
-55 dBc OR Better |
| 10 |
OUTPUT STABILITY (Peak Power) |
0.3 dB OR Better |
| 11 |
BLACK LEVEL STABILITY |
0.2 dB OR Better |
| 12 |
VIDEO PARAMETER |
| 12.1 |
AMP. Frequency Response |
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| |
fv + f MHz |
LIMITS (dB) |
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MAXIMUM |
MINIMUM |
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-4.43 TO –1.25 |
-20 |
- |
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-1.25 TO –0.75 |
+0.5 |
- |
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-0.75 |
+0.5 |
-4.0 |
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+0.5 |
+0.5 |
-0.5 |
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+1.0 |
+0.5 |
-0.5 |
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+1.25 |
+0.5 |
-0.5 |
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+2.0 (Ref) |
0.0 |
0.0 |
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