VDL/HFDL

Mark, would you mind explaining thoroughly either VHF data link or high frequency data link and how cal I find out if such a communication systems are installed on b737-300?

VHF (118.0 - 136.975 MHz) and HF (2100 - 28,000 KHz) can be used for voice or data communications.

For data in the VHF range..... pretty much just ACARS  will use a dedicated VHF Comm Transceiver. The flight crews will (at a minimum) have two Comms for ATC communication. If your aircraft have a third Comm and it shows "data" in one of the two tuning windows, you can almost bet a ACARS system is using it.

As for HF, its use in aviation is dwindling. Crews will still use it for position reporting to ARINC while over the oceans if their aircraft are not outfitted with some sort of satellite communication system. I would have to guess that data transmission via HF is not used anymore. HF is very susceptible to atmospheric conditions. Reliability issues are a main drawback.

AFIRS is now a major player in data or voice communications from aircraft to ground monitors. Satellite installations on aircraft are continuing to be "the" choice for future communication requirements.

It doesn't depend on third TRX, Rockwell Collins TRX P/N: 822-1047-003 provides both voice and data communication so two set of aforesaid unit can provide signals for ACARS Management Unit

I'm going to push back on this one.....

Any modern VHF Comm can transmit voice or data, but they aren't used for both at the same time. 

There would have to be a change over relay, either internally or externally. If what you are suggesting is true, then voice can override data or vice-versa. Would a ACARS system like its data transmission interrupted halfway through or the pilot's talking to ATC to be cut off for a data-burst?

I can swap a VHF Comm radio into any position. They don't care if it's analog voice or digital bits they're transmitting-receiving, but I have never seen one radio used for both functions at once.

Thank you for your reasonable explanation. How can I find if the Rockwell Collins transceiver can be used for VDL mode2 system?

I'm not sure what VDL mode2 is.

I see no reason why a Collins transceiver being used today cannot transmit any kind of digital data.

VDL=VHF Data Link
ICAO VDL Mode2
(Doc 9776)

Three Comm Tuning Panels. Left and right, voice. Center, data.
  
     
  
The center can be voice or data. This one selected to data. Normally in data 100% of the time.
  
     
  
Center VHF note to crew under the fuel shutoff levers.
  
     
  
ACARS menu on Flight Management System CDU.