Custom Products from Masters Communications

What does it do?
The VOX-10 board attaches to the DRA-45 radio adapter available from Masters Communications.  It develops a PTT logic signal (ground) when sufficient audio is available to activate the circuitry. The DRA-65 and DRA-70 have this circuit built directly onto the radio adapters main circuit board.

This board is not recommended for use with the DRA-30 and RA-25K because of insufficient audio level to trip the circuit.
In my testing, it took a setting of "0" in VARA, 100% in Windows, and the level pot on the DRA-30 (the channel feeding the VOX) wide open to make the test tone trip the PTT reliably. You may have to set the TX modulation pot really low because of the increased settings to make the VOX-10 respond on the other channel. With the DRA-45, level settings are much easier. When necessary, an attenuator can be built and placed onto the H1 or H2 header to make the transmitter audio level setting less touchy. Contact Kevin (link at bottom of page) for details on how to build an audio attenuator for the DRA-45.

Why do I need it?
This board is used with digital applications that don't have C-Media Hardware PTT capability built into the programs to control the native GPIO3 on the CM119A, allowing the PTT to be generated directly by the radio adapter (sound card). Namely, FT4 FT8 and SSTV, among others require VOX. The VOX-10 board attaches directly to the radio adapters DB9 and has another DB9 where the radio cable then attaches to. The VOX-10 board has a DB9 male on one end, and a DB9 female on the other, and is sort of a "pass through" design. All pins are routed 1:1 between the DB9 connectors, with the exception of pins 3 and 9 for reasons explained in the detailed description. You can even install a DRA DIN-6 Adapter or RJ45-6 Adapter onto the VOX board.

Easily movable on-board jumper "shorts" allow this product to be used with either the DRA-30, DRA-45. Additionally other jumpers allow you to choose Left or Right audio from the radio adapter, enable the radio adapters Red PTT LED, and enable the false PTT LED illumination protection.

Detailed Description:
This board produces a PTT logic signal (ground) when sufficient audio level is available to activate the circuitry. There is no additonal PTT LED on this board to indicate a valid PTT. The VOX-10 circuit is designed to back-feed its PTT signal into the radio adapter and illuminate the Red PTT LED on the radio adapter. This function is enabled by placing the back-feed Jumper JU1 on the VOX-10 and disabling the PTT false illumination protection on the radio adapter. That is accomplished by placing JU4 on the DRA-30, or JU6 on the DRA-45.

Audio for the VOX's input can be sampled from either the Left or Right output channel using a movable jumper JU5. 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 using the Left Channel for VOX drive, and the Right Channel for your transmit audio. Turn the Left Channel level pot (R16) up the whole way, and set the Right Channel level pot for the correct audio level to your transmitter.

Important:
Make sure you have the left channel audio enabled and routed to the DRA's DB9 by placing a jumper on JU5 on the DRA-45 or JU3 on the DRA-30.

2-pin jumpers JU3 and JU4 configure the DB9 properly between the DRA-30 and DRA-45. This is done with a square arrangement of four header pins. Two shorts go side-by-side in one direction for the DRA-30, and are rotated 90 degrees for the DRA-45. Silk screen on the printed circuit board and depiction on the schematic image plainly shows what to do. When arranged in the "A" or DRA-30 position, pin 9 on both DB9's are grounded. When arranged in the "B" or DRA-45 position, pin 9 is connected from one DB9 to pin 9 on the other DB9 through a heavy circuit trace to allow a external power source to pass power through to the audio amplifiers or filters - if required, as long as JU2 (on the DRA-45) is placed in the B position.

VOX is enabled any time JU5 is installed and sufficient audio is detected by the circuitry. Removing JU5 disables VOX. Keep track of the jumper by hanging it off of one pin.

Parts List:
Q1 - MPSA13 Darlington NPN
R1 - 1k 1/8w
R2 - 10k 1/8w
R3 - 100k 1/8w
C1 - 10uF 16V Electrolytic - Non-Polarized
C2 - 1uF 35V Tantalum - Observe polarity!
D1, D2, D3 - BAT-43
J1 - DB9 Female
J2 - DB9 Male
JU1 - JU4 - 2-pin .100 male header pins (blue)
JU5 - 3-pin .100 male header pins (blue)
5 - shorts
2 - Screws (4-40 X 3/8")
1 - VOX-10 Printed Circuit Board

Available assembled and tested (A&T), or as a complete kit with all parts and screws.

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VOX-10 Options:

VOX-10 Kit $10.00 USD VOX-10 Assembled and Tested $20.00 USD

Shipping amount is calculated at checkout for shipping to most locations Worldwide.

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Product of Masters Communications, all rights reserved.
Specifications may change without notice.
Images are property of Kevin Custer - W3KKC
Board layout by Kevin Custer - W3KKC
HTML March 10, 2020, W3KKC All Rights Reserved!