Twin Engineers
Exciter for TV Transmitter 
 
 
Model No.: TW/TV/EXCITER
 
The exciter consists of following modules namely:
 
  • 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
Individual functional block description is as follows:
 
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.
 
 TECHNICAL SPECIFICATION OF THE EXCITER
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
  +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  
 

fv + f  MHz

LIMITS (dB)

    MAXIMUM    MINIMUM
  -4.43 TO –1.25 -20 -
  -1.25 TO –0.75 +0.5 -
  -0.75 +0.5 -4.0
  +0.5 +0.5 -0.5
  +1.0 +0.5 -0.5
  +1.25 +0.5 -0.5
  +2.0 (Ref) 0.0 0.0
 
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