Desired Physical Characteristics

Modular Configuration—Each transmitter shall consist of discrete modules. Each module will be installed in one or more appropriate cabinets, wired, and tested in the manufacturer’s plant to minimize assembly at the transmitter site. All transmitter wiring shall be clearly labeled at each termination. The transmitter is expected to include the following or similar modules:
  • System Monitoring and Control
  • Local and Remote Control via IEEE 802.3 Local Area Network interface
  • Uninterruptible Power Supply providing continuous power to the transmitter Local and remote control sub-system. The transmitter control sub-system will provide complete control and diagnostic information to the LAN interface during absence of power input.
  • Exciter and 8VSB modulation
  • Intermediate Power Amplifier (if required)
  • High power amplifier as required to produce licensed transmitter power output
  • RF Switching, filtering, impedance matching, reject, and test loads
  • High voltage beam supply
  • Calibrated RF power measurement system
  • Heat exchanger with redundant coolant pumps and multiple fans for each HPA
  • A chain hoist with adequate capacity to change power amplifier tubes
  • Interlock system meeting the requirements of IEC-215
Transmitters using liquid cooling will include the following major components:
  • Outside heat exchanger, with multiple direct-drive fans
  • Redundant coolant pumps with local and remote switching of pumps
  • Coolant storage tank with level gauge
  • Particle filter
  • Pressure gauges
  • Temperature and flow sensors
  • Test and reject load cooling
  • Interlocks for test and reject load, amplifier flow, and reservoir levels

High Power Amplifier Sub-System

The IOT and associated magnet and RF circuit assemblies shall be removable from the front of the transmitter incorporating wheels and quick disconnect RF, electrical, and plumbing fittings. The assembly shall incorporate a positive wheel locking mechanism to prevent accidental movement while in operation.

Electrical, Electronic Characteristics, and Performance

Power Rating—Each transmitter shall be designed for and be capable of operation at the average DTV power specified in the test and acceptance specification.
Metering to permit proper maintenance and roubleshooting, including:
  • Collector or Cathode Current
  • Collector or Collector-to-Cathode Voltage
  • Body Current
  • Coolant Temperature
  • Output Power
  • Reflected Power
  • Filament Voltage
  • Filament Current
  • Focus Magnet Current

High-Power Amplifier Characteristics And Performance

Protection circuitry shall be incorporated to protect the IOT by removing high voltage and drive power from the IOT in the event of an internal tube arc or beam current overload. Any overload condition shall cause the control circuits to remove and automatically reapply high voltage to the amplifier. Three overloads within a short period shall shut down the amplifier and activate the appropriate overload fault indicators. Over-current protection devices shall comply with all specifications of all tube manufacturers approved for the transmitter to avoid violating the manufacturer’s warranty. The protective circuitry shall also protect the IOT from other faults that may cause damage to the tube or the tube’s circuitry including but not limited to extreme collector temperature, VSWR, and body or grid currents. Supplier shall describe its method of IOT protection and the means by which its tube protection circuitry complies with each approved tube manufacturer’s warranty requirements.

IPA/Driver Exciter System

Each exciter shall include all necessary switching, control, and status monitoring. The 19.39 Mb/s transport stream input to the exciter will comply with SMPTE 310M or DVB-ASI standard. The exciters shall convert the 19.39 Mb/s transport stream to an 8VSB-modulated carrier. Exciters shall perform frame data randomization, Reed-Solomon encoding, data interleaving, Trellis coding, segment and field sync insertion, pilot insertion and filtering, and be fully compliant with ATSC A/53 Standard and applicable FCC Regulations.
The exciters shall include automatic signal processing for the precorrection of the signal to compensate for linear and non-linear errors in the transmitter amplifier stages and to provide group delay correction for group delay errors introduced in the output RF system, as well as an RF combiner when present.

RF Output System

The RF system shall be of coaxial and/or waveguide construction, and RF inputs and outputs shall be standard EIA coaxial flanges.
A low loss, constant impedance-type band-pass filter shall be supplied with each transmitter to meet the FCC Mask requirements. The filter shall be supplied with reject and ballast loads.
The IPA/Driver meeting the following requirements:
  • Modular design and easily serviceable
  • Designed for optimum linearity and fully compliant with ATSC transmission standards
  • Rated for at least 120 percent drive power output level
  • The IPA and its power supply shall have redundancy incorporated in the design. The IPA shall be provided with an output ferrite circulator for protection against excessive VSWR or an inadvertent disconnection from the IOT amplifier.
The RF system shall be supplied with a motorized antenna/load RF switch, liquid cooled test load, and calorimeter power measuring equipment. The switch shall be provided with integral interlocks as a part of the transmitter control system to permit easy connection of the transmitter to the test load.
Two precision calibrated directional couplers shall be provided on the output of the RF system ahead of the antenna/load switch for station use. One indicates forward power, the other reflected power.

High Voltage Supply

The high voltage supply shall be oil filled and self-contained. It shall be designed for operation outdoors over a temperature range of 20 to þ45 degrees C (at 100% humidity). Weather resistant panels shall cover all connections. The unit shall be rated for continuous on-air operation at the transmitter’s full rated output power plus 20%.
The high voltage supply shall include the capability to adjust the output voltage to the requirements of various tube types and incorporate a step-start device to protect components from large inrush currents.
The high voltage supply shall be capable of operating from the commercial power service at each site. A step-up transformer shall be provided and installed if necessary.
The AC line control cabinet shall control AC power to the beam supply. To protect the IOT amplifier during an overload condition, the AC input to the beam supplies shall be removed in less than 10 milliseconds by high-speed vacuum contactors. The line control cabinet shall include circuit breakers for protection against over-current and short circuits. Mechanical interlocks for both the line-control cabinet and the beam supply shall be incorporated for personnel safety.

Transmitter Control

Overall transmitter system control, monitoring, and diagnostic functions shall be accomplished using an intuitive, high resolution, industrial grade, color Graphical User Interface located in the system control cabinet. GUI screen selection and commands shall be controlled via a touch screen interface. It is desired that basic control functions also be available using hard-wired control buttons located on the control cabinet front panel. These basic functions should include as a minimum; beam voltage on/off, filament on/off, black heat, power raise/lower, and remote/local control.
The following parameters shall be monitored and available for display on the transmitter control/monitoring system:
  • Transmitter output power
  • Transmitter reflected power
  • IPA drive power
  • Reject load power
  • System interlock status
  • All system overloads
  • Power supply voltages and currents
  • System block diagrams to aid in fault location
  • AC line voltages
  • Phase loss status
  • A summary of active and inactive fault conditions shall be stored and available for view on the transmitter GUI.
  • Circuitry shall be provided to lower the transmitter power output in the case of increased VSWR. Decreasing VSWR shall cause the power level to increase until the original output power is restored.
  • All logic control memory shall be backed up so as to return the transmitter to its mode of operation immediately preceding an AC power failure of any duration.

RF Combiner

When multiple RF amplifiers are used to meet specific transmitter power output or multiple transmitters operating on different carrier frequencies are fed to a single ended passive transmission system, an RF Combining until will be employed. In such cases, the RF combiner and all transmitter units shall perform as a system. The system will be required to meet all FCC requirements as though it were operating as individual components. The RF combiner shall not degrade the spectral performance of any single transmitter.
The combiner will include an RF sample point at each input and output of the combiner.
The combiner must be capable of continuous operation across the temperature and humidity range as the transmitter with all inputs from all transmitters operating at 110% of theirTPO.
RF insertion loss shall not exceed 0.4 dB from input terminals to output terminal with all inputs operating at transmitter TPO levels.
Channel isolation shall be greater than 35 dB between any input and any other inputs Group delay shall be within + 20 nanoseconds across the channel pass band.
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