Custom Products for the Digital Radio Amateur Enthusiast

Quick Explanation:
Placing the VOX jumper on the 2-pin header enables VOX.
Removing the VOX jumper on the 2-pin header disables VOX.
JU6 enables / disables VOX.
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, and SoundModem have been modified / upgraded to support PTT operation on the C-Media sound card on a chip, like the CM119A that we use in our radio adapters. PTT on the CM119A is derived by toggling GPIO3, and that in turn keys a transistor that keys the radio. We call this "C-Media Hardware PTT".

Unfortunately, other programs don't have Hardware PTT support that's built into VARA, but there are two ways to work around this.
One solution is additional computer programming. Additional PTT information for ARDOP, and other programs is available from our FAQ page.

The other solution is VOX. Our DRA-SR has VOX capability in addition to the Hardware PTT keying of the transmitter. Unlike the DRA-65, '70, and '80, this product has VOX DELAY that adds hang-time to PTT. The delay time is set using the "DLY" control on the front panel. The delay time is variable from 0 seconds (absolutely no delay) to 1.5 seconds when the control is fully clockwise.

VOX operates differently on the DRA-SR as compared to the SignaLink USB. Both Left and Right audio output channels are available for you to configure VOX detection and Transmiter drive.
Just make sure you configure the program to put "Modem signals on both Left and Right channels" otherwise VOX and/or audio to the transmitter may not work.

VOX drive is selected by JU1.
It is strongly recommended that LEFT channel audio is selected at JU1. VOX drive is adjusted by R16 - an internal blue trimmer pot.

Transmitter drive is selected by JU5.
It is strongly recommended that RIGHT channel audio is selected at JU5. This allows transmitter audio to be adjusted in level by the front panel "TX" pot.

If there's no option to configure the digital program to put audio on both channels, adjust the settings in Windows to make the Speaker Audio "MONO". This duplicates the source audio on both channels regardless of which channel it appears on originally.

Detailed Operation:
Placing a jumper "short" onto header JU6 enables the integrated VOX feature of the DRA-SR. JU1 chooses 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 on the front panel.

To use the VOX feature 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 (with the internal R16 control) and transmitter modulation level with the front-panel "TX" level control.

When the USB cable on the DRA-SR is initially plugged in, the red PTT LED will briefly illuminate. This is expected if a jumper (shunt) is installed at location JU6.

DRA-SR VOX set-up:
R16 is an internally mounted control that's used to set VOX sensitivity or VOX drive. If this control is set too low - unreliable VOX operation may occur. Setting this control too high can add unwanted delay time. The optimal setting allows for fast but reliable keying of the radio with no unwanted drop-outs. A setting of 50 to 60% is generally good with nice strong levels coming from Windows and the application.

Initially - set R16 (Left Audio Level - center of circuit board) to 60% clockwise.
Set R14 (TX) level on the front panel to minimum.

We recommend the following default jumper settings to use VOX:
JU1 - L
JU2 - A
JU3 - Absent - remove for normal digital operation.
JU4 - This header only exists on DIN6 model. RX Baud Jumper 1200 - 9600 - Set as necessary to match your desired RX baud rate.
JU5 - R
JU6 - Install for VOX - Remove for Hardware PTT.
JU7 - PWR LED solid of flash.
JU8 - RX audio attenuator - Remove jumper for 20dB of attenuation.
JU9 - Right TX audio attenuator - Remove jumper for 20dB of attenuation.

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. The setting of R16 affects the VOX operation as detailed above. Carefully adjust the TX control on the front panel (clockwise) for sufficient modulation of the transmitter. Remember - if you don't have VOX operation or TX audio - your program (or Windows) needs set up to duplicate the data (audio) on both the Left and Right channels.

When VOX operation isn't required, please pull jumper JU6 (red header).
Doing so ensures the fastest transition time between TX and RX, and maximizes the transfer speed.

Email Kevin Custer for additional support.

SignaLink® and SignaLink USB® are registered trademarks of Tigertronics.
The use of the name SignaLink and/or SignaLink USB is only in reference to this product.
No infringement for such use is intended.
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