Here are some images of the Gables Engineering Inc. dual radio two way communication panel. This panel, known as panel G-2349A, is a DZUS mount panel for radio control. The goal is to control the (AM) communications tranceiver/radio. (In other words, not to control the navigation radio equipment.) This device is built in September 1999.
The frequencies on this panel can be set between 118,00 and 135,97 MHz. The channel spacing is 25 kHz. Remind that the frequency indication is 'rounded'. x,x25 MHz is shown as x,x2 and x,x75 MHz is shown as x,x7. The airband frequencies are typically between 108 and 137 MHz. Between 108,00...117,95 MHz is used for VHF Omnidirectional Range (VOR) short range radio navigation (NAV), so not for voice communication. Between 118,00...137,00 MHz is for two way 'phone' communication (COM). This means that this panel is designed for two way phone use. This panel doesn't have programmable memory frequencies nor a preset for the International Air Distress (IAD) guard frequency (121,50 MHz) for emergencies.
Further reverse engineering will be done. For now the set of photo's is shown below...
It is possible to set the simplex (receive or transmit on the same frequency) frequency using two knobs for MHz an kHz setting. There are two frequencies that can be set; the left and the right part of the panel. There is a [T/R] switch in the middle to select the desired Transmit/Receive frequency; the left or the right channel. There's a test button that is likely to activate some self test of the radio equipment. There's also an audio volume knob equipped with a on/off switch. In the full CCW position, the volume knob is 'locked' in the off position. By rotating the knob clockwise, the radio is switched on and the volume can be set to the desired position. Above the frequency readout is a indicator light to indicate which channel is selected. There's also backlight for easy operation in low light conditions.
In which airplane this panel is used, is unfortunately unkown to me. The panel is black, so it's probably not used in a Boeing of an Airbus since Boeing panels are brown and Airbus panels are grey.
At the rear of the panel is one connector for all the communications. This is a well known (ITT/Amphenol) circular type connector with shell size 20. There are 41 contacts installed of size 20. This is also known as a 20-41 configuration; shell size 20 and 41 pins. Remind that this panel is a 'dumb device'. As usual in avionics, this panel is only equipped with switches and lights. This panel has to be connected to other equipment (like the transceiver) to be able to operate. Since there are multiple contacts for each MHz/kHz position, there are may contacts needed. There's a diode board installed that is likely used to reduce the number of contacts on the rear panel. There reverse engineering has to be done yet, but it's rather safe to assume that the diode matrix is used to 'compress' the channel data to limit the needed contacts. The (500 Ohms) variable resistor for volume control is directly connected to pins (e), (f) and (g). Where contact (f) is the CCW connection, pint (e) is connected to the CW connection and pin (g) is the variable contact of the potentiometer. Also the panel lighting is connected directly to the connector pins. The normally open contacts of the test button are connected to pins (J) and (K). The [T/R] switch is partially connected to the pins at the connector. At first glance is seems that the other half of the connector is used to control the incandescent indicator lamp above the frequency readout to indicate which channel is selected. Some more investigation has to be done here...
The inside of the device is artwork. All switches are well built mechanical switches. There are some (probably current limiting) resistors installed and there are a lot of wires. The frequency readout is mechanically. Since some electronics (like microcontrollers and electronics displays) are more sensitive for failure, this 'mechanical design' is very durable. Well machine brass parts are installed for interconnection. There are no tie-wraps installed, but wax cord. This makes the wire harness very durable. There is a white plastic disk installed to create a litte more drag to the volume knob to prevent unwanted rotation and create a 'click' when turned to the off/on position. The downside is that plastic hardenes over time and the platic disk is cracked at the locking bolt due to ageing of the plastic. All the lamps are incandescent lightbubls. Nowadays the use of incandescent lighbulbs is rather odd since the use of led lighting is more logical since the power losses are way less and leds are more durable and less sensitive for failure. 'The final verdict' is that the device is well built and is a piece of artwork that can last for years!
Since it's hard to find documentation about avionics devices, I can use some help.
I have some questions like:
In which aircraft type/model was this pane used?
With which transceiver did this panel work?
Does anyone have documentation of this instrument?
If you have more information of documentation of this device, please let me know.
13-12-2023: My goal is to document this device as complete as possible. After this is completed I'll redesign the circuit. My idea is to remove the diode board and design a replacement circuit board with a Atmel microcontroller. So the controller can 'read' the panel settings and the controller can control the panel lighting for example. The idea is to used the serial data output to control an external Kenwood Th-D7E ham radio transceiver. The Kenwood TH-D7E can be controlled via the serial port, so the panel can be functional again in some way. The transceiver is blocked so it can't transmit (by accident) on the airband. The idea is that the test button is used as a toggle switch to control the panel lighting and as a push button to open the squelch. The indicator lamps above the frequency readout can be used as a receive indicator instead of an always on lamp.
I also want to find out if it's possible to remove the mechanical limits so the frequency range is extended especially to 144...146 MHz. This makes it possible to also use this panel for the 2 meters VHF FM band. The Kenwood TH-D7E has also access to the 144...146 MHz band and switches automatically between FM and AM depending on the selected frequency. The limit is though that the channel steps is limited to 25 kHz instead of the usual 12,5 kHz. But depending on the software it's thinkable to used the test button for increasing the indicated frequency +12,5 kHz. The good thing though is that the transceiver is dual band, so two 2 meters frequencies can be monitored at once or the airband and one 2 meters frequency at the same time.
Well, plenty of ideas. A limit is that the frequency range is within 100...199 MHz since the first digit is always a one. So the coverage will probably be the AM airband and the 2 meters FM ham band.
Plan B is to control a Yaesu FT-8x7 transceiver. This transceiver family can also be controlled using a serial port. The limit is that the transceiver is a single band, so switching between the left and right channel is applicable.
First let's find the schematic or reverse engineer the design as as start.
Note: Gables Engineering Inc. is contacted for (technical) documentation that may help. The request is pending...