Custom Products for the Digital Radio Amateur Enthusiast

IMPORTANT NOTES:
(1) - This Mixer, when paired with the TX transfomer option board, provides balanced transmit audio for connection at the RADIO port to radios that require a balanced TX audio connection. The receive audio input at the RADIO port is unbalanced and there is no option at this time for transformer coupling of the receive audio. There are no radios that we are aware of that don't support an unbalanced receive audio connection - therefore no balanced receive audio input via a transformer option is available (or required).

(2) - The DRA-3M-RJ45 Transformer model is NOT compatible with any pre-made Radio Cables or Plug-&-Play Jumper Modules designed for the SignaLink USB. This model requires a custom built cable.

(3) - One jumper wire is required to be installed into the configuration socket to connect receive audio to/from the RADIO port. A single jumper wire from either pin 4 or pin 5 to pin 16 on the transformer board is required. This jumper allows the radio's receive audio to be connected to either pin 4 or 5 of the RJ45 connector. Either one can be used and there is no preference for one over the other.

The input and output stages are compatible with commercial radios that use "balanced" inputs and/or outputs. This model provides a transformer to create a balanced transmit audio source that's not tied to ground. This output is truly balanced and floating - isolated from any other potential - including ground. The plus and minus balanced TX output is available at RJ45 pins 1 and 2 respectively.

Detailed Description of the DRA-3M-RJ45 Transformer Option Mixer:
This product is an active mixer that allows two applications using separate sound cards or hardware modems to be connected to a single balanced audio radio - simultaneously. Configuration headers and jumpers allow selection of baud rates (audio types) for matching the correct audio for the application. A relay eliminates any PTT incompatibility issues - even when a sound card with transistor keying is used - (DRA-36 or similar).

The Mixer uses a high-performance, low-noise TL074 op-amp and requires a source of clean power (12 VDC at less than 100mA - provided externally). A LM386 audio amplifier stage is included for radios that require elevated TX audio. The internal "TX Drive" control allows you to set the right transmit level for your radio - even when a non-amplified (DRA-36, SignaLink USB or similar) sound card is used. The TX Drive control is factory set to unity gain. The receive audio paths are unity gain as well and present a ~10k impedance to their source for minimal loading. Readjustment of audio levels may be necessary with some radios. The input and output stages are compatible with Commercial radios that use "balanced" inputs and/or outputs. This model provides a transformer to make a balanced transmit audio source that's not tied to ground. This output is truly balanced and floating - isolated from any other potential. The plus and minus balanced output is available at RJ45 pins 1 and 2 respectively.

Input Ports
Two identical Mini-DIN-6 input ports are available on the back panel. These are Mini-DIN-6 female connectors on both the DIN6 and RJ45 models. These ports are identical mechanically and electronically. It doesn't matter which one is used for what application. Easily movable on-board jumper "shorts" allow the Mini-DIN-6 input ports on this board to be configured for "1200" or "9600" baud - no soldering required. Most HF radios will require the 1200 setting. 9600 baud packet and VARA FM Wide will use the 9600 setting.

Output Port
The DRA-3M-RJ45 Transformer model is NOT compatible with any pre-made Radio Cables or Plug-&-Play Jumper Modules designed for the SignaLink USB. This model requires a custom built cable and one jumper wire to connect the receive audio to the RADIO port.

Power:
This is NOT a passive mixer. It's active and requires power to operate. An optional AC power adapter is available. This power adapter has been tested for RF emissions and is nice and clean. The DC Power Jack is a standard coaxial DC socket 2.1mm X 5.5mm. A DC Pigtail Power Cable for connecting to a conventioal 12V DC power supply or battery is also available. Center pin is positive - sleeve is negative. Acceptable voltage range is 10 - 16 VDC at less than 100mA. The power supply MUST supply clean voltage or unacceptable operation will result.

Detailed Technical Description & Audio Performance:
This unit produces a PTT (keyed ground) when any sound card or Modem connection is producing a PTT signal.

Transmit audio from the sources is mixed together, buffered for isolation, and routed to the radio. This audio is not switched or gated - it's simply mixed together. Receive audio from the radio is split into two sources which are individually buffered for isolation and routed to the sound cards or modems. These active stages eliminate interaction of audio levels that can change when simple resistive (only) mixing and splitting practices are employed.

Receive audio "Type" (either "1200" or "9600") [narrow or wide] can be selected from configuration headers for each sound card port. It's possible to select 1200 for one and 9600 for the other - but this might not be a functional configuration depending on the exact equipment being utilized. Frequency response of all paths is flat and have guaranteed specifications from 50 Hz to 20 kHz at -0.5dB.

PTT Operation:
The relay is a reed type for high reliability and super fast switching time. Typical switching delay is less than 0.5 (1/2) Millisecond. TX audio level is adjustable from a few 10's of mV to 10 Volts P-P. TX audio level is normally set for unity gain (1:1) in/out. The PTT circuitry is active "OR" logic and doesn't require much source current to ground to become active.

Parts List:
Click here for Parts List.

Jumper Settings:
Click here for Header / Jumper settings and other board connection assignments.

Recommended powering requirements:
The board needs to be supplied with 12 VDC. See the detailed notes above in the "Power" section.

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Product of Masters Communications, all rights reserved.
Specifications may change without notice.
Images property of Kevin Custer - W3KKC
Board layout by Kevin Custer - W3KKC.
HTML July 12, 2024, W3KKC All Rights Reserved!