When considering the radio equipment installed on a typical airliner, there are two strong driving factors. First, is that most of the equipment installed is required by regulations in the aircraft's country of registry for IFR flight. Dual VHF transcievers are standard, and HF radios are required for operation in airspace beyond VHF range. Altitude reporting transponders are required for air traffic control. For thunderstorm avoidance, weather radar must be installed. Also, radar altimeters are on board for use during initial climb, final approach, and for the ground proximity warning system.
Operators doing considerable overseas flying often have satellite communications installed, and tend to select either Inmarsat or Iridium communications services. As airborne broadband internet becomes a more common service to airline passengers, expect more sophisticated satellite communications equipment to appear on the 737NG and other medium range jetliners.
The second driving factor is cost. Airlines are always on tight budgets and tend to buy the minimum equipment to allow safe and reliable operations. The radios tend to be very basic in features, but extremely reliable. Heavier gear will cost companies more in fuel burn over time, so "lighter is also better."
In the table below, note that most of the Boeing 737NG radio equipment is manufactured by one company. The radio suite is actually an option selected by the airline when the aircraft is ordered. Rockwell-Collins and Honeywell offered the best combination of performance, reliability, and price, and were chosen for the vast majority of Boeing 737NG radio installations.
Rohde and Schwarz is another manufacturer of radio equipment that is found in quite a lot of jetliners. Their radios, like Rockwell-Collins' equipment, are "tough as nails," and offering basic features.
|Equipment Type||Manufacturer / Model||Modulation Type||Power|
|HF Voice Transceiver||Rockwell Collins HFS-900D||A3E (AM)
J3E (Upper Sideband)
|VHF Voice Transceiver||Rockwell Collins VHF-2100||A3E (AM)||25W|
|DME (962 to 1150 MHz Xmit)||Rockwell Collins DME-900||P (Timed Pulses)||316W|
|Radar Altimeter (4300 MHz)||Rockwell Collins LRA-900||F3 (FM Radar)||400mW|
|TCAS||Rockwell Collins HFS-900D||P9 (Data on pulses)||400W|
|Transponder (1090 MHz)||Rockwell Collins TPR-901||P9 (Data on pulses)||631W|
|WX Radar (9.3 Ghz)||Rockwell Collins WXR-2100||P0 (Pulsed Radar)||120W|