Broadcast

Reliability

The ATP420 is a 1U rack-mounting unit with all of the main functions contained on a single circuit board. It contains no fan or disk and dissipates less than 10W. No special measures are therefore needed to cool the unit or provide it with ventilation.

The unit has a bypass relay which operates to connect the video input directly to the output should the power to the unit fail. A battery within the unit ensures that the page data data and operating parameters are retained for up to 72 hours without power, thus ensuring that the unit can restart transmission as soon as power is restored.

Technical Specification

• Teletext System - World System Teletext, 625 line EBU SPB 492, CCIR Teletext System B
• Video in, Video Out, Monitor Out - 1Volt Composite 75W terminated BNC connectors
• Text Input - 1Volt Composite BNC loop through - unterminated
• Linear Distortion - 2T pulse and bar ratio < ± 0.5%
  Tilt < 0.25%K
  Chroma/Luma Gain inequality < 1%
  Chroma/Luma delay inequality < 10nS
• Non-Linear Distortion - Differential Phase < 1°
  Differential Gain < 1%
• Return Loss - > 36dB
• Signal/Noise Ratio - > 65dB rms ( 0.2 - 5.5 MHz )
• Amplitude - 462 mV adjustable ± 20%
• Filter - 100% roll off cosine
• Threshold - 150mV below black level
• Sync to Text delay - 12 µS, front panel adjustable

Master / Standby Operation

For complete peace of mind when transmitting a full teletext service the ATP420 has been designed to operate with a second unit and an ATP920 service selector to provide an automatic backup for a non-stop transmission.

The inserter monitors a range of operating conditions to provide a control signal to the ATP920. It even contains a teletext decoder to monitor the final output. If any fault occurs the ATP920 will switch to the standby unit. A serial connection between the two units is used to ensure that the database of the off-air unit is kept up to date by the on-air unit.