Custom Products for the Digital Radio Amateur Enthusiast

Background - VOX PTT operation of the DRA-65, DRA-70, and DRA-80:

Quick Explanation:
Placing the VOX jumper on the 2-pin header enables VOX.
Removing the VOX jumper on the 2-pin header disables VOX.
The following header number enables / disables VOX.
JU7 - DRA-65 and DRA-70
JU6 - DRA-80
The VOX header has a red bottom (plastic spacer) over the pins close to the board surface. All other headers are a different color.

Detailed Explanation:
Applications like VARA FM, VARA HF, Fldigi, Direwolf, and SoundModem have been modified / upgraded to support PTT operation directly from the C-Media sound card chip (CM119A) that we use in our radio adapters. PTT on the CM119A is derived by toggling GPIO3 (pin 13), and that in turn keys a transistor or relay - and that keys the radio. We call this "C-Media Hardware PTT".

Unfortunately, some programs don't have Hardware PTT support. In that case, one solution is to use VOX. Our DRA-65, DRA-70, and DRA-80 have VOX capability in addition to C-Media Hardware PTT.

VOX operates differently on the DRA-65, '70 and '80 as compared to other similar sound cards. Unlike some other units out there, both Left and Right channel audio is available for you to configure the device. Normally - one channel is configured to drive the VOX detection circuitry (you choose which channel). The opposite channel is then used to drive the transmitter modulator. We suggest a particular default for this set-up. You may need to configure the device differently for your application, depending on how the application is written.
Just make sure you configure the program to put "Modem signals on both left and right channels" otherwise VOX and/or transmitter audio may not work.

Movable on-board jumper "shorts" enable the integrated VOX feature on the DRA-65, DRA-70, and DRA-80. These jumpers allow you to choose which channel (Left or Right) feeds the VOX detection circuitry. When actuated by sufficient audio, the VOX creates a PTT signal to key the radio and illuminate the Red PTT LED. When VOX operation isn't desired, you pull jumper off of the red header and operate the DRA under C-Media Hardware PTT.

Detailed description that applies to the DRA-65, DRA-70, and DRA-80:
The DRA-65, DRA-70, and DRA-80 are basically the DRA-45 and DRA-50 with additional circuitry which produces a PTT logic signal (a switched ground) when sufficient audio level is available to activate it. The Red PTT LED is used to to indicate a valid PTT. The VOX circuitry is designed to "back-feed" the PTT logic on the radio adapter and illuminate the Red PTT LED. On the DRA-65 and DRA-70, VOX is enabled by installing a jumper on JU6 and JU7. It's the same two jumper numbers for both boards. For the DRA-80, VOX is enabled by installing a jumper on JU6. The DRA-80 doesn't have a JU7.

Audio for the VOX's input is sampled from either the Left or Right output channel using a movable jumper JU1. Many programs duplicate the audio to both channels. It's recommended to use the opposite channel than you're using for transmitter audio to feed the VOX board. That way, you can control the audio level to the VOX independently from your transmitter audio. We recommend you follow the configuration and procedure below. JU1 performs the same function on all three boards.

To use the VOX feature on the DRA-65, '70, or '80, you must turn the volume of the application up pretty high, as it takes a lot of audio to trip the PTT. Most applications duplicate the audio (data) on both channels. In this case, the Left channel is used to feed the VOX circuitry, and the Right channel will feed your transmitters audio input. Doing so allows individual control of VOX sensitivity and transmitter modulation level.

When the USB on the DRA-65, 70, or '80 is initially plugged in, the red PTT LED will briefly illuminate. This is expected if a jumper (shunt) is installed at locations JU6 and JU7. For VOX operation, JU7 and JU6 jumpers are installed. Pull both for normal hardware PTT. These jumpers are normally shipped from the assembler pre-installed. Remember - the DRA-80 doesn't have a JU7. JU6 is the only jumper associated with the VOX function on the DRA-80.

DRA-65 specific information:
Initially - set R16 (Left Audio Level) to maximum and R14 (Right Audio Level) to minimum.

The following jumper settings are necessary for VOX operation:
JU1 - L
JU2 - A
JU3 - Absent
JU4 - Absent
JU5 - Installed
JU6 - Installed
JU7 - Installed

The Red LED will illuminate when there's enough audio present to trip the VOX circuitry. This may require setting the volume level on the computer higher to achieve enough audio to trip the VOX reliably. Then, adjust the volume of R14 to sufficiently drive the transmitter.

When VOX operation isn't desired, you can pull jumper JU7 (red header) and operate the DRA-65 normally. Optionally - JU6 can also be pulled.

DRA-70 specific information:
Initially - set R16 (Left Audio Level) to maximum and R14 (Right Audio Level) to minimum.

The following jumper settings are necessary for VOX operation:
JU1 - L
JU2 - A
JU3 - Absent
JU4 - Absent
JU5 - A
JU6 - Installed
JU7 - Installed
JU8 - As necessary.

The Red LED will illuminate when there's enough audio present to trip the VOX circuitry. This may require setting the volume level on the computer higher to achieve enough audio to trip the VOX reliably. Then, adjust the volume of R14 to sufficiently drive the transmitter.

When VOX operation isn't required, you pull jumper JU7 (red header) and operate the DRA-70 normally. Optionally - JU6 can also be pulled.

DRA-80 specific information:
Initially - set R16 (Left Audio Level) to maximum and R14 (Right Audio Level) to minimum.

The following jumper settings are necessary for VOX operation:
JU1 - L
JU2 - A
JU3 - Absent
JU4 - As necessary.
JU5 - R
JU6 - Installed

The Red LED will illuminate when there's enough audio present to trip the VOX circuitry. This may require setting the volume level on the computer higher to achieve enough audio to trip the VOX reliably. Then, adjust the volume of R14 to sufficiently drive the transmitter.

When VOX operation isn't required, you pull jumper JU6 (red header) and operate the DRA-80 normally.

Email Kevin Custer for additional support.