DigiRig Digital Modes Interface

The "Digirig Mobile" is an extremely compact & rugged "sound card interface" for amateur radio digital modes operation. This device is available directly from it's manufacturer in Grand Junction, Colorado for USD $50. Their somewhat confusing website is at:

    http://digirig.net

"Soundcard Interface" strictly speaking is incorrect, because the DigiRig is not just an audio coupler for a computer sound system.  It contains it's own internal sound system, in a manner similar to a TigerTronics SignaLink.  Unlike the Signalink, the DigiRig does not use VOX PTT keying. It uses hard PTT keying via either the classic serial-port RTS handshake line or via CAT data command strings. 

The device contains:

• A C-MEDIA CM108 sound chip. This is the same sound chip used in many current laptops and USB audio "dongles".
   
• A Silicon Labs CP-2102 serial<-->USB interface chip. This is the same serial<-->USB interface chip used in many current Yaesu and Kenwood radios for memory programming and/or CAT control. If you have one of these radios, the required driver is already on your system.
   
• A tiny USB hub that combines the sound chip and the serial chip into a single USB connection to the computer being used. In turn, drivers on the computer creates a generic "USB PnP Sound Device" for the sound system and a virtual COM port with changeable com number for the serial port.

Versions of Windows, XP or higher, will automatically download and install the required drivers.  No separate explicit install of drivers is required. 

The serial port can be used two ways: 

• As the traditional comport handshaking-line RTS transmit-keying method widely used with digital-mode soundcard applications, where the serial data lines are not used. In this mode, only a single cable is needed between the Digirig and the radio, since the audio jack/cable also carries the open-collector RTS PTT keying line.
   
• Or as an actual serial port with TXD and RXD lines for "CAT" (Computer Aided Tuning) control of modern transceivers that can be controlled by sending command strings over the serial data lines.  An alternate cable with the two-prong Kenwood/Wouxon/Baofeng hand-held plug, available from the manufacturer, allows the serial port in this device to be used for memory programming on these radios as well as TX PTT keying. 

The single PC board is contained in a square cross-section aluminum extrusion 1 inch (2.54cm) x1 inch (2.54 cm) x 1.5 inches (3.8 cm) long.   One end has two 4-contact "TRRS" (Tip-Ring-Ring-Sleeve) 3.5 mm jacks.  One is for the TX audio, RX audio and classic RTS transmit keying.  The other is the RXD and TXD serial connections used for CAT control.   (All pics taken with an iPhone 6S+ and tweaked in IrfanView)

The other end has a single USB-C jack for connection to the computer being used. The manufacturer offers a USB-C to USB-A cable with an interesting twist: The cable is curly and stretchy like an old  telephone handset cord, or a hand-mic cable.

Inside the housing is a single tiny PC board with surface-mount components.  This is version 1.8 of the device which was just released when I received my Digirig at the beginning of March 2022.

The other side of the board has several solder-bridge pads for setting configurations. The board includes support for Icom's screwy single-wire serial bus called CI-V.

The manufacturer offers several pre-made cable assemblies to connect to various radios, including to the two-prong plug used by Kenwood, Wouxun and Baofeng handhelds. 
    The designer seems totally enamored of CAT-type control interfaces. DigiRig offers a cable kit for the Yaesu FT-8xx radios (FT-817, FT-818, FT-857, FT-891, FT-897, etc) that provides TWO cables: The 6-pin mini-DIN cable for TX/RX audio hookup, and the 8-pin mini-DIN serial cable for CAT-style PTT keying.  
    In a similar manner, DigiRig offers a pair of cables for the larger Kenwood radios equipped with the  "ACC2" 13-pin full-sized DIN connector, assuming you will use the separate serial port on these radios for CAT-based PTT control. 

In both cases, the DIN-plug cables also carry the traditional ground-to-transmit hard-keying PTT line, giving you the choice of classic RTS handshaking-line transmit keying or using the second (serial) cable for CAT-type command-string transmit keying.

[Tying up the serial port just for PTT control is a significant disadvantage -- it prevents using the 8-pin mini-DIN port on the Yaesu radios, or the serial com port on Kenwoods,  for logging applications or for activating external "smart" amplifiers, antenna tuners or "screwdriver" mobile antenna controllers.]  

Further, many older soundcard digi-mode apps only support the traditional RTS transmit keying method; they don't support the dozens of proprietary radio-specific CAT commands for TX keying. either directly, or through "middleware" apps such as FLrig or HamLib.

If you want to fabricate your own cable(s):   

In the past, cables with the 3-contact TRS 3.5mm plug molded on (i.e. stereo headphone/audio cables) were readily available, while ones with the 4-contact TRRS plug were very hard to find.  This has now changed radically. A vast array of 4-contact TRRS 3.5 mm plugs, jacks and molded cables are now available from eBay and Amazon. 

Note that there are two conventions for the use of the 4-cond plug.

• One, first used by analog video camcorders decades ago to combine left & right stereo audio and composite video on a single cable, uses the sleeve contact for the COMMON/GND contact, just as headphones have for over a century with the larger 1/4-inch plug.
   
• The other convention, starting with Apple's usage on the iPod Classic 5th Gen (first iPod with video as well as audio), iPhones and iPads places the COMMON/GND connectionon on the second ring instead, and the mic-in line on the sleeve.  Now nearly all cellphones (that still have headphone jacks!), tablets and small laptops use this convention. 
  
  This is part of a complex "smart jack" scheme for detecting if earbuds or headphones without a mic, or a headset with a mic are inserted into the jack.  If a head set with a mic is plugged in, the device's internal mic is disabled.
      If headphones-only without a mic (and a 3-conductor TRS plug) are plugged in, the longer sleeve contacts ring 2, causing GND/COMMON to short the mic-in sleeve contact to ground.  The device then keeps it's internal built-in mic live.  This TRRS pinout is sometimes referred to as the "CTIA" (Cellular Telecommications Industry Assn) standard.

DigiRig uses the classic pinout with COMMON/GND on the sleeve of the plug.  Take this into account when buying TRRS patchcords to cut up for making cables.

A useful tool for experimenting with the DigiRig, and for making up custom cables, is this break-out block. It lets you connect bare flying leads from any kind of cable to the TRRS jacks in the DigiRig, using set-screws. 
    This cable is also useful for breaking out the TRRS combined speakers+mic jacks of phones, tablets or small laptops, for use with other soundcard interfaces that have separate TX and RX jacks. This adapter is available from Amazon, for USD $9.00, at:

https://www.amazon.com/Poyiccot-Plated-4-Screw-Terminal-Connectors/dp/B07PQTKMM7/ref=sr_1_19?keywords=trrs+jack&qid=1646156924&sr=8-19