Avionics Bending: Audio Panel Integration for the L-1011 Trainer

Tim Joransen and myself discussed how to do realistic audio panel integration for the simulator. So, to use a Virtual Air Traffic Control System (in our case VatSIM) we are currently thinking about using XSquawkbox.

To make the cockpit experience as realistic as possible from an audio perspective we need to have a number of discrete audio channels that can be fed into and received from the 4 audio panels in the cockpit. What and where are the four audio panels?

1. Captain's Audio Selector Panel on the aft center console
2. First Officer's Audio Selector Panel on the aft center console
3. Second Officer's Audio Selector Panel on the lower Flight Engineer's Console
4. Observer Audio Selector Panel to the left of the observer's seat

L-1011 Audio Selector Panel Locations - From Delta Pilot's Reference

Most audio panels made by Gables Engineering have a very similar pin configuration. And allow for a number of external components to be connected. For the L-1011 project, here are the external elements that connect to each audio selector panel:

• Headset (All Stations)
• Boom Microphone (part of the headset) (All Stations)
• Oxygen Mask Microphone  (All Stations)
• Hand Microphone (Captain, F/O and S/O only)
• Overhead Speaker (Captain and F/O only)
• Yoke R/T and INT Switch (Captain and F/O Only)

Here are the different audio channels that need to be fed to the Audio Select Panel to make the simulation as realistic as possible:

1. VHF COM 1 Audio (xsquawkbox)
2. VHF COM 2 Audio (xsquawkbox)
3. VHF COM 3 Audio (xsquawkbox)
4. HF COM 1 Audio (tbd)
5. HF COM 2 Audio (tbd)
6. VOR 1 Audio (xplane via plugin)
7. VOR 2 Audio (xplane via plugin)
8. ADF 1 Audio (xplane via plugin)
9. ADF 2 Audio (xplane via plugin)
10. Marker Beacon (xplane via plugin)
11. Ground Proximity Warning (xplane via plugin) 
12. Interphone (within the simulator)

The audio panel also routes the microphones for each of the audio stations to the respective channels. For the simulator here is the proposed mapping:

1. VHF COM 1 Microphone (to xsquawkbox)
2. VHF COM 2 Microphone (to xsquawkbox)
3. VHF COM 3 Microphone (to xsquawkbox)
4. HF COM 1 Audio (tbd)
5. HF COM 2 Audio (tbd)
6. Voice Recorder Output (tbd)
7. Interphone (within the simulator)

Of course there is still the Passenger Address (PA) system that would be, of course, part of the L-1011 however, for the purpose of building the simulator we will not worry too much about the PA system. We will not integrate the PA into the audio panel, however, the L-1011 has a Passenger Address panel on the overhead panel and we might consider connecting that. 

L-1011 Trainer Installation: S/O Console and Center Panel Power-Up - Continued

L-1011 F/O Audio Panel and SELCAL Panel Installation

The power up of our L-1011 panels continues. Jim and myself powered up a total of 4 additional panels and also installed the necessary cable bundles for the instruments. Today we powered up the F/O side audio panel, the SELCAL panel located on the aft center console (see below). Currently the Captain's side and the F/O side audio panels are different. The F/O panel is actually just a placeholder for now; it will be replaced with an audio panel identical to the Captain's next week.

L-1011 SELCAL and F/O Audio Panel

We further powered up the Cabin Pressurization module on the upper Second Officer console as well as the APU Control panel located on the lower S/O console (see below). 

L-1011 Pressure Control and APU Control Panels

The Lockheed L-1011 Cabin Pressure Control panel is a really neat instrument. It has two large windows with a tape behind them for adjustments. The window on the left hand side sets the Flight Altitude and the one on the right sets the barometric pressure (see below).

L-1011 Cabin Pressure Control Panel

Besides the panel light up, Jim started preparing the Pilot's and First Officer's side consoles for the installation of the audio connectors. The side console holds connectors for the headset an headset-boom microphone; a handheld microphone and the audio connectors for the oxygen masks.

Jim Blasco working on the F/O side audio connectors.

L-1011 Trainer Installation: Audio Panel and Dual ADF Head Power Up

This evening I ran the cabling for the first audio selector panel as well as the dual ADF panel. Both are located on the aft center console. The audio selector requires a lot of cables due to the fact that each of the audio channels has its own cable. The two remaining components that are not powered up yet on the aft console are the weather radar selector and the first officer's audio panel.

Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 8)

As you probably know, navigation aids, such as VOR, DME, ILS and ADF, are identified by Morse code (CW). Typically they are identified by a 3 or 4 letter identifier like: PDK, JFK, CHA, etc. The standard frequency for the CW signals is 1020Hz. However, in some cases NAV aids also carry a voice signal that can give weather or AWOS or other information. In the case of ADF stations, that signal can also be co-located with AM radio stations. So most audio panels provide the ability to "filter" out Morse code to provide a clear and uninterrupted voice signal. To enable this filter most panels, like the one that I use from Gables Engineering, have a "VOICE ONLY" type setting. The audio panel that I am intending to use for the L-1011 simulator has a large orange momentary switch that toggles the CW filter on and off. The video below shows the Voice Only filter for CW in action:

I used the Kennedy VOR (JFK) as the Morse code and the Kennedy International D-ATIS information as the voice ... this is a combination that does not really exist in reality and I just combined them for this demonstration. Just doing a rough measurement it appears the filter covers a frequency range between about 920 - 1120Hz. The filter has very little to no impact on the voice signal, however, the effect on the CW is very obvious.

Below is a quick refresher on Morse Code:

International Morse Code

Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 5)

Today is all about the Gables audio selector panel and seeing it in action. For the test setup I have configured 3 audio channels that are fed to the VHF-1, VHF-2 and VOR-1 channel on the audio panel. Here is a description from the L-1011 flight manual on how the audio panel works (taken from a Delta Airlines L-1011 Operating Manual):

1. Microphone Switchlights 

Push to select desired transmitter. Integral light illuminates. VHF switch lights also select respective receive function without independently selecting the corresponding receive switch. A mechanical interlock prevents the selection of more than one transmitter at the same time.

2. Control Knobs

Push to monitor audio. Push again to discontinue monitoring audio. All receivers may be simultaneously monitored. Rotate knob to adjust volume.

3. Voice Only 

Filters out the out the Morse code (CW) signal.

Below is a short video demonstrating the features of the Gables audio selector panel that I intend to use for the L-1011 project:

Note: The computer voice that says "This is VHF one" and other is there for testing only. I mix it into the audio channel that is connect to help me assure that I am cabled correctly. Also, the ATC feeds are not from X-plane or VATSIM quite yet ... they are live ATC audio feeds from the Internet. 

Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 4)

Each crew member has three different ways of sending microphone input to the audio system.

1. There is a microphone attached to the headset worn by each crew member. 
2. A hand microphone is provided for the Pilot and First officer, and,
3. A microphone is installed in the oxygen mask

Each microphone is routed to the respective radio via the Mic Select switch on the audio panel. A radio will transmit when Push To Talk (PTT) switch is pressed. The pilot an First officer have 3 ways of keying the PTT:

1. The pilot and first officer yoke have a Push To Talk (PPT) switch on each yoke. The following two images show a typical Boeing 737 yoke with the PPT switch located on the forward facing side of the left hand grip.

B737 Yoke and PTT

B737 Yoke and PTT

2. Each crew station in the cockpit is also equipped with a hand microphone. The image below shows a typical Telex hand microphone as used on the L-1011 and many other aircraft type. The push button on the top of the hand mike has the same function as the PPT switch sown in example 1.

Hand Microphone PTT Switch 

3. The microphone can also be keyed with a small switch located directly on the audio selector panel. In most cases, this PPT switch would be used in conjunction with the Oxygen Mask microphone.

Audio Selector Panel PTT

For the simulator project, all three ways of keying the microphone results in a "transmit" setting on the flight simulator. 

Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 3)

Now that I have decided on a basic architecture for the audio integration it is time to do a power up test of both the Gables radio head as well as the audio selector panel. Both components take 24-28VDC power input. I am driving them with 24VDC and that works just fine.

Gables Radio Head and Audio Selector Powered

At this point the radio head is powered but not yet connected to an ARINC 429 receiver or transmitter. The audio panel is powered and the built in amplifier and "Voice Only" selector are working. I also cabled a temporary L-1011 Headphone and Hand-Mike break-out panel ... this way I am able to connect the David Clark headset for testing. 

Original L-1011 Hand-Mike and Headset Connector Panel

Below is a short video that show the setup in action. I connected a scanner radio listening to Atlanta Center to the Gables Audio Selector's VHF-1 input. The audio is not yet coming from the simulator. 

Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 1)

Now that we have at least one primary flight instrument, the HSI, under our belt (see the previous 15 postings) I will now move on to something very interesting, which is radio integration into X-Plane. Here is the stack that I will be working with for the next few weeks:

Gables Multi Function Radio Head and Gables Audio Selector Panel

The two instruments in the picture above are a GABLES G6984 radio head and a GABLES G2930 audio selector panel. The G6984 uses the ARINC 429 protocol for radio data and is a perfect next step for the ARINC 429 work I have been doing lately. Unlike the the HSI, which only required sending ARINC 429 data to the device, the G6984 will require bi-directional traffic; radio frequencies from the radio and FMS data to the radio head.

In the L-1011 cockpit there are three identical audio selector and radio head combinations; one for the Pilot, one for the First Officer and One for the Second Officer. For the test setup I will also use a Hand Mike and a David Clark Headset (rather have a Telex, but I don't have access to one). Below is a picture of the input and output:

Gables VHF COM, Hand Mike and David Clark Headset

The L-1011 cockpit has two overhead speakers that can be used for monitoring audio without the need for a headset. For the test setup I will only use one of the two speakers. The speaker is powered and has an amplifier built in.

Original L-1011 Cockpit Overhead Speaker

Tomorrow, we will look at t detail analysis of the audio signals needed for a realistic integration of X-Plane and a simulated ATC system.

Avionics Bending: Audio Selector Panel (Analysis)

I chose a set of Audio Selectors made by Gables Engineering for the Lockheed L-1011 project. The L-1011 used a number of different audio selectors, depending on the avionics package selected by the customer. This particular audio selector panel is from a TWA L-1011.



The case for the selector panel is split into two pieces: a top plate that unscrews with four screws, and a "U" shaped enclosure that also fastens with four screws.


Top: The top view of the audio selector is dominated by the brown circuit boards for the push button selectors.


Right hand side view


Bottom view


Left hand side view
Each of the audio selector push buttons has a dual function: (a) when depressed, the audio source is switched to the amplifier and, (b) turning the push button regulates to volume of the selected source. The volume is changed with a potentiometer on the backside of the switch, as can be seen below.


Each audio selector has a primary and an alternate amplifier. The amplifier can be selected with a toggle switch on the lower left hand side of the audio selector panel.

Original Flight Hardware: Audio Selector Panel

There are several audio selector panels in the Lockheed L-1011 cockpit. Two of them are located on the center console and one of them is located on the flight engineer station (as seen at the end of this posting). There are number of selectors across the top of the panel which select the microphone connection to a specific radio or PA system.


Here are the individual switch functions:

• Microphone Selector Switch - Connects microphone outputs to respective transmitter or interphone system.
• Audio Selector Switch - Connect headset to respective receiver or interphone. Push for ON-OFF, rotate for volume control.
• Voice Switch (bottom right) - filters code signals and improves voice reception
• Range Switch (next to voice) - filters voice signals and improves code reception
• Speaker Switch - enables captain or f/o to use individual speakers. Push for ON-OFF rotate to adjust volume.
• Amplifier Select - NORM - normal amplifier, ALT - using alternate amplifier.

Panel Locations