Unit 2 – IF Modulator -1-
Unit 2 – IF Modulator 1. Audio and Video Modulator: 1.1. Function: This module function is to generate two carriers: one in 45.75 MHz and the other in 41.25 MHz. The first is modulated in AM-VSB by a video signal and the other one is modulated in frequency by an audio signal. 1.2. Block Diagram: 1.3. Technical Description: 1.3.1. Video Modulator: The transistor Q1 oscillates in the crystal frequency (45.
Unit 2 – IF Modulator The video signal peak is detected through IC8 and through IC9 and it is differentiated with the level adjusted through R45, in order to extract the dc component. The IC9A output has a dc level related to the video signal not taking into account the synchronizing pulses. The 100% video measurement is adjusted through R72 in the meter with a video signal with 100% APL.
Unit 2 – IF Modulator 2. Technical Characteristics: 2.1. General Characteristics: Operation Temperature: ___________________________________________________________________ 0 to 45°C AC Power Supply: ________________________________________________________ 220Vca / +36Vcc (optional) Maximum consuption: __________________________________________________________________________15W Dimensions: _____________________________________ Height = 44mm; Width = 482.
Unit 2 – IF Modulator 2.6. Audio Carrier: Frequency: ______________________________________________________________________________ 41.25 MHz Frequency Stability: ______________________________________________________ 2x 10-6 (Thermal Chamber) Deviation:___________________________________________________________________ +/- 25 KHz (Adjustable) Mono: Pre-emphasis: ___________________________________________________________ 75 µs (according to mask 4) Freq.
Unit 2 – IF Modulator 3. Reference Mask: 3.1. Frequency Response Mask 1: 3.
Unit 2 – IF Modulator 3.3. Video Pre-Corrector Mask 3: 3.4.
Unit 2 – IF Modulator -8-
Unit 2 – IF Modulator 4. Frontal and Back Panel: 4.1. Frontal Panel: Each element in the panel has the following function: 1. Meter: For video, audio and IF measurements. For a video signal with 100% APL the meter will indicate 100%. In the audio position, the measurement of 100% in the meter will indicate the correct deviation. In the IF position, the measurement of 100% corresponds to 0 dBm level in the output. 2. Video/Audio: Measurement selector switch.
Unit 2 – IF Modulator 4.2. Back Panel: Each element in the panel has the following function: 1. AUTOM, C AND BATTERY (OPC): - AUTOM: output to external command. When the video is on, this output is short circuit to the ground (50mA maximum current). - C: EXTERNAL CONTROL: Lower output IF level by ground contact. - BATTERY (OPC): Battery input +36V (optional). 2. VIDEO IN: Video input 75 Ohms impedance (unbalanced) and 1 Vpp level. 3.
