Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 2)

Overview

There are quite a large number of audio sources that pilots use during flight and on the ground. Not all audio sources are really meaningful in a simulator cockpit, however, I will attempt to create and implement as many as possible. So here are the radio sources, as well as other sources that produce audible signals, most commonly found on large transport aircraft:

1. Very High Frequency (VHF) radios are mostly used for communication and navigation. VHF COM is used both in the air and on the ground to talk to controllers as well as listening to weather services like AWOS. VHF NAV is used for navigation, however, also carries audible signals in the form of Morse Code (for VOR and ILS identification and sometimes DME) and/or voice signals for other automated signals. 
2. High Frequency (HF) is used for company communication from the ground to aircraft and the other way around. HF really has not much of use in a simulator, however, I will still cover it as part of this effort because maybe there is something fun that can be done with it (maybe SELCAL integration).
3. Automatic Direction Finder (ADF) uses a band that is in many cases also used by AM radio broadcasts. The NAV aids are also known as Beacons and also have Morse Code for Beacon identification. 
4. Marker Beacons are part of the Instrument Landing System (ILS) and typically consist of 3 radio Beacons called; Outer-, Middle- and Inner-Marker. Each of them has a different frequency that is represented in the cockpit by goth a visual queue (a blue, orange and white light) as well as an audible signal in the form of 3 different tones. 
5. Passenger Address (PA) System allows the cockpit and cabin crews to make those lovely announcements about keeping your seat belts on until at the gate and look out the left window to see the Grand Canyon. 

The most interesting sources to implement with the simulator are the VHF, ADF, Marker and PA sources. VHF COM is most frequently by using either a synthetic ATC system or by connecting to a simulator service like VATSIM run by real people who act as flight controllers. My plan is to implement with VATSIM for the VHF COM radios. 

Technical Implementation

One of the core issues is that most flight simulators output a stereo-mix of audio, however, for the Audio Panel I need discrete output from each simulated audio source. Some of the audio output will need to be created from scratch, here are some thoughts on the signals:

• VHF Voice - use the VATSIM output.
• VHF NAV - generate Morse code based on the NAVAID name
• ADF - generate Morse code and mix in some type of radio or other signal
• AWOS - use text to speech generator 
• Marker - use sound generator to create marker beacon signal

All in all the integration for each of the 3 radio head/audio selector panel combinations will look as follows: