Friday, September 23, 2016

Second Generation Ku/Ka Satcom (PP792) Taking Shape

PP792 Ku/Ka Satcom Block Diagram

The form and fit of the second generation Ku/Ka satcom system is firming up in preparation for the next meeting of the AEEC subcommittee in October hosted by Gogo at their  Chicago facility

The goal of PP792 is a lighter and smaller satcom system with as simple a wiring interface as possible.  This objective is met by the following enhancements:
  • Removal of one LRU (the modman), an ARINC 600 4 MCU box typically located far from the antenna penetrations (such as in an E-Bay).   The modman functions are moved to the KRFU.  The modman Ethernet distribution is restricted to a single interface per ARINC 664 domain, plus any set aside for broadcast services.  The PP792 concept assumes IFE or other systems will distribute the Ku/Ka data link accordingly (whereas in ARINC 791 the Modman could be a stand-alone IFE server).
  • Removal of the coaxial interface from the KRFU to the modman (by virtue of moving the modems into the KRFU).  The KRFU is installed in close proximity to the antenna penetrations offering the shortest cable runs.
  • Encourage the provision within the KRFU to host two or more modems to accommodate broadcast and roaming features.
  • Removal of all control connections save one Ethernet bus.  The control connector specified in ARINC 791 offers 66 size 22 (22 AWG wiring) connections; PP792 would reduce that to four.  In a slight departure from ARINC 791, the control cable will terminate with the KRFU, not the KANDU, noting that the KRFU is installed much closer than the KANDU.
ARINC 791 Part 1 Bulkhead Interface Control Connector
  • Promoting the cross-wiring of the ARINC 429 IRU interface as specified in ARINC 791 Part 1 to connect from the KANDU to the KRFU.  The KANDU function is reduced to a power supply.  All beam steering is assumed within the KRFU or in the Outside Antenna Equipment (OAE).
  • Move the last stage transmit amplifier to the OAE.  Many expected flat panel technologies integrate the amplifier as a part of the array of emitters. Antennas using a single-ended input are encouraged to utilize a fail-operative design such that a single failure results in degraded functionality, not loss of functionality.
  • Consider a second location for fittings 5 and 6 (5a, 6a) that better fit a tandem aperture installation, along with optimized penetration zones for the connectors.  Neither Airbus ARINC 791 and Boeing proprietary fitting locations are aligned today.  The hope is that PP792 fittings 1, 2, 3, 4, 5a, 6a, and 7 will prescribe a common goal for support of large and small flat panel antennas.
ARINC 791 fittings and bulkhead penetration zones with single/dual apertures highlighted

  • Bombardier and Embraer have both joined the subcommittee to ensure coverage to regional jets that may be using a tail-mounted antenna.  Their installations are a bit different in that only the ARINC 791 modman is within the pressure vessel.  For PP792, where the KRFU is described as an ARINC 836 flange mounted LRU, for these aircraft it is more likely to be in the ARINC 600 4 MCU form factor LRU.
The subcommittee is reviewing ARINC 791 Part 1 DO-160 qualification standards. These evolve with new revisions to DO-160, along with better understandings gained by service experience.  The addition of Bombardier and Embraer brings some additional complications due to their slightly different categorizations.

Other subcommittee work includes agreement on maneuvering limits for beam steering and means to modify the spectral mask in real time using flat-panel apertures that vary with both elevation and skew angles.

Peter Lemme
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Follow me on twitter: @Satcom_Guru

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Peter Lemme has been a leader in avionics engineering for 35 years.  He offers independent consulting services largely focused on avionics and L, Ku, and Ka band satellite communications to aircraft. Peter chairs the SAE-ITC AEEC Ku/Ka-band satcom subcommittee developing PP848, ARINC 791, and PP792 standards and characteristics. 

Peter was Boeing avionics supervisor for 767 and 747-400 data link recording, data link reporting, and satellite communications.  He was an FAA designated engineering representative (DER) for ACARS, satellite communications, DFDAU, DFDR, ACMS and printers.  Peter was also lead engineer for Thrust Management System (757, 767, 747-400), supervisor for satellite communications for 777, and manager of terminal-area projects.

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