Unit 1 – Introduction 2. General Technical Descriptive: 2.1. IF Modulator (for transmitter): This is the input module. It is a professional audio and video modulator. The audio and video signals are applied to their respective input for the modulation process in IF (41 to 47 MHz]. The audio and video input impedances are 600 balanced Ohms and 75 unbalanced Ohms, respectively. 2.1.1. Video processing: The video signal passes through linearity correction circuits and then is applied to the 45.
Unit 1 – Introduction 2.3. Amplifier Levels: 2.3.1. Comment/Composition/Origin: The RTU1000T is composed of four 250W amplifier modules that are combined through 3dB hybrid circuits. A 50W amplifier and 1: 4 hybrid module excite the final modules. All the amplifiers are completely in solid state. 2.3.2. Protections/Signaling: Each 250W amplifier has a VSWR protection (Voltage Stationary Wave Ratio), temperature and limiting power.
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 8. Power Supply: 8.1. Function: The power supply function is to generate +12V and -12V voltage suitable to supply the modulator. 8.2. Technical Description: The transformer T1 reduces the input voltage for the rectifiers D1 to D4. The positive and negative voltage obtained after the rectification and filtering through C1 and C2 are regulated through IC1 and IC2 to obtain +12V and -12V voltage to supply the Modulator. 8.3.
Unit 2 – IF Modulator 9. Power Supply (optional): 9.1. Function: The switched power supply has the function to generate +12V and -12V voltages from the input voltages AC or from the +36V battery (opc). 9.2. Technical Description: The input voltage, after transformer T2 and diodes D1 and D4, supplies the PWM IC1. If there is no AC the battery voltage supplies the circuit. The pulses generated by IC1 commute the transistor Q1 and switch the voltage over the primary T1 at 25 KHz frequency.
Unit 2 – IF Modulator 10. Meter Circuit: 10.1. Function: The meter circuit allows, through the selector switches and meter, the measurements of the video modulation, audio modulation and the IF level. 10.2.
Unit 3 – Channel UP Converter 1. Channel UP converter: 1.1. Introduction: This module converts an IF signal, into “a” UHF band channel, maintaining its characteristics and the same bandwidth. 1.2. IF filter and amplifier AGC (for transposer): The filter and IF amplifier establish the necessary bandwidth to the input signal and supply a gain in it, maintaining a constant level, through an AGC loop. It is used only in the transposer equipments. 1.3.
Unit 3 – Channel UP Converter 3. IF filter amplifier: 3.1. Function: The IF filter establishes the adequate bandwidth to the input signal and the IF amplifier supplies the gain for this signal, maintaining a constant level, through AGC loop. 3.2.
Unit 3 – Channel UP Converter following circuits are enabled.
Unit 3 – Channel UP Converter 4. IF Pre-distortion linearity: 4.1. Function: It corrects the non-linearity and/or intermodulation that are generated at the final stage of the transmitter amplification. 4.2. Technical characteristics: Frequency band: ______________________________________________________________________ 41 to 47 MHz Input level: ____________________________________________________________________ -4.0 dBm ± 1.
Unit 3 – Channel UP Converter 5. Automatic Level Control (ALC): 5.1. Function: The Automatic Level Control corrects the transmitter output peak sync power due to the variation gain of the amplifiers. 5.2. Technical Description: This circuit has a total attenuation of 1dB, allowing controlling the power to positive and negative variation of 0.5dB. The command occurs through the obtained voltage from the TV monitor through wire identified by the CAP cord.
Unit 3 – Channel UP Converter 6. Channel UP Converter: 6.1. Function: The channel UP converter function is to convert the IF frequency (41 to 47 MHz) to a determined channel in UHF. 6.2.
Unit 3 – Channel UP Converter 7. PLL protection: 7.1. Function: This circuit function is to turn off the transmitter. 7.2. Technical Description: The DC voltage that comes from the channel converter, more precisely from the channel converter Led diode, is applied to the comparator through diode D1 by resistor R1 and reaches circuit integrated IC1pin 3.
Unit 3 – Channel UP Converter 8. UP Converter supply -12, +12 and +24V: 8.1. Function: The power supply function is to generate -12V, +12V and +24V voltage suitable to supply the UP Converter. 8.2. Technical Description: The main AC input voltage is reduced by the transformer T1. T1 has two secondarie winds, one for the +24V and the second for the +12V and –12V supplies. D1, D2, D3 and D4 rectifiers the secondary voltage that is filtered by the capacitor C1.
Unit 4 – 50W Exciter 1. 50W Exciter: 1.1. Introduction: This module amplifies the signal power that comes from the channel converter, to the 50 W level, maintaining its characteristics and the same bandwidth. 1.2. Protections and Monitoring: We have for these functions: VSWR Circuit: it protects the amplifier module transistors, when the output stationary wave is superior to 4%. This circuit acts in the output transistors gates.
Unit 4 – 50W Exciter 3. Amplifier protection: 3.1. Function: This module function is to protect the amplifier modules against an excessive VSWR, RF power and temperature. 3.2. Technical Description: The informations from forward RF power and VSWR are obtained through the Directional Coupling detectors from the amplifier output. The proportional voltage to the RF forward power supplies the isolator amplifier integrated circuit IC5A. This amplifier output, supplies IC5B and IC2A comparator circuits.
Unit 4 – 50W Exciter 4. Power supply input: 4.1. Function: This circuit function is to protect the power supply, if there is a short-circuit and provides the amplifier current monitoring. 4.2. Technical description: The +32Vdc voltage that comes from the three-phase fixed power supply supplies the fuses F1 and F2. The fuse output F1, by resistors R1 and R2, supplies the 50W final amplifier. The amplifier current can be monitored by the voltage drop over R1 and R2.
Unit 4 – 50W Exciter 5. 2W Amplifier: 5.1. Function: The 2W UHF amplifier stage amplifies the channel converted to 2W maximum level. 5.2. Technical characteristics: Gain: ________________________________________________________________________________________ 30 dB Supply: _____________________________________________________________________________________ +32Vdc Total current: ___________________________________________________________________________________ 1 A 5.3.
Unit 4 – 50W Exciter 6. 50W amplifier: 6.1. Function: The 50W exciter amplifier stage, receives the 2W amplifier signal and delivers it to 1:4 divider of 250W amplifiers with a maximum 50W power. 6.2.
Unit 5 – 250W Amplifier 1. 250W Amplifier: 1.1. Introduction: This module amplifies the RF power that comes from 1:4 divisor to 250W, then they are combined to obtain the 1000W RF power, maintaining its characteristics and the same bandwidth. 1.2. Protections and Monitoring: For these functions, we have: VSWR Circuit: it protects the amplifier module transistors, when the output stationary wave is superior to 4%. This circuit acts in the output transistors gates.
Unit 5 – 250W Amplifier 3. Amplifier protection: 3.1. Function: This module has the function to protect the amplifier modules against an excessive VSWR, RF power and temperature. 3.2. Technical Description: The informations from forward RF power and VSWR are obtained through the Directional Coupling detectors from the amplifier output. The proportional voltage to the RF forward power supplies the isolator amplifier integrated circuit IC5A. This amplifier output, supplies IC5B and IC2A comparator circuits.
Unit 5 – 250W Amplifier 4. Power supply input: 4.1. Function: This circuit function is to protect the power supply, if there is a short-circuit and provides the amplifier current monitoring. 4.2. Technical description: The +32Vdc voltage that comes from the three-phase AC power supplies the fuses F1 and F2. The F1 fuse output by resistors R4, R5 and R6 supplies the left 125W amplifier. The F2 fuse output, by resistors R1, R2 e R3 supplies the right 125W amplificer. 4.3.
Unit 5 – 250W Amplifier 5. 250W amplifier: 5.1. Function: Its function is to amplify the power that comes from 1:4 divisor to the 250W output level. 5.2.
Unit 6 – +32V power supply 1. +32V Power Supply: 1.1. Introduction: The function of this module is to provide a +32Vdc voltage at a 90 A maximum current. For this, it is used a three-phase rectifier totally controlled by 6 SCR diodes. 1.2.
Unit 6 – +32V power supply 2. +32V Three-phase control power: 2.1. Function: The module three-phase control power function is to generate synchonized triggers pulses to the rectifier bridge power SCR. This circuit is also responsible for the over current, the over voltage and fail phase protection. 2.2. Block Diagram: 2.3. Technical Description: The three-phase power control is obtained by three integrated circuit IC4, IC5 and IC6.
Unit 6 – +32V power supply To protect the over voltage, the integrate circuit IC3A compares an output voltage sample obtained by R50, R54, and R55 to a reference voltage obtained by diode zener D24. If the output voltage exceeds the determined value, the integrated circuit output IC3A passes to the high level acting in the tiristor diode gate SCR Q12 that, in its turn, puts the transistor emitter Q11 to the ground, consequently its collector too.
Unit 6 – +32V power supply 3. +32V power supply transient suppressor: 3.1. Function: The transient suppressor eliminates the high frequency transients generated by the SCR diodes fast commutation. 3.2. Technical Description: The RC circuit that is connected in parallel to the SCR’s from rectifying bridge, is used to decrease the switching transients, from anode to catode of each SCR. 3.
Unit 6 – +32V power supply 4. Temperature control: 4.1. Function: Its function is to protect against the power supply temperature increasing. 4.2. Technical Description: Through a NTC (VR1) thermistor that is set up over the SCR’s heat sink of the three-phase rectifier bridge, a sample voltage is compared to a reference voltage that is obtained by R4 and trimpot R1.
Unit 7 – Cabling and attributes 1. VSWR Command: 1.1. Function: Its function is to protect the equipment if there is an antenna excessive VSWR. 1.2. Technical Description: The detected sample by the directional coupling is applied to IC1 integrated circuit. IC1 output is compared to the adjusted reference value by trimpot R13. If VSWR exceeds the pre-adjusted limit, IC2 integrated circuit output passes to the high level, conducting transistors Q1 and Q2.
Unit 7 – Cabling and attributes 2. Three-phase transient suppressor protection: 2.1 Function: Its function is to protect against voltage peaks in the three-phase circuit network that occurs because of atmospheric discharges or transients. 2.2 Technical Description: This circuit is composed by six varistors: VR1, VR2, VR3, VR4, VR5 and VR6. The varistors VR1, VR4 and VR5 are interconnected Phase to Phase and the varistors VR2, VR3 and VR6 are connected Phase to Ground. 2.3.
Unit 7 – Cabling and attributes 3. TV monitor: 3.1. Function: The TV monitor function is to detect the output RF signal and final amplifier, providing the video carrier output power reading and audio carrier and the video signal monitoring that have been transmitted. 3.2. Technical Description: The obtained signal through the directional coupler supplies the monitor input, by connector J1. The resistors R14 and R15 provide 50 Ohm termination for interconnecting cabling.
Unit 7 – Cabling and attributes 4. Notch filter: 4.1. Function: Its function is to attenuate the adjacent channel spurious undesirable to the transmitter operation 4.2. Introduction: We have in the transistorized equipments, after the final amplifier, besides the desired channel, spurious of –9, -4.5, +4.5, +9 and sometimes ±13.5 MHz. These spurious usually appear through the amplification of the output transistor, affecting the adjacent channels.
Unit 7 – Cabling and attributes 4.5. Characteristic Curve at the Network Analyzer -2° Harmonic: 4.6. In practice Below there are two RF signal diagrams in the Spectrum Analyzer. 1° without trap filter: 2° with trap filter: In the second chart the –9.0 MHz spurious should be at least –60dB, regarding to the video carrier.