Custom Products for the Analog & Digital Radio Amateur Enthusiast

Schematics of MUX-25 REV6 - Click to download a high quality PDF.

MUX-25 REV1 thru REV5 Parts List

REV6 MUX-25 Parts List

Overview of MUX-25:
The MUX-25 board was produced from a schematic supplied by a couple of guys in Canada - VA3UV and VA3RQ. The radio connector is designed for a Kenwood TKR-750/850 repeater, but should work with just about any repeater or radio as the signals are generic in nature. The analog side is designed to connect to an AllStar node, and the digital side is D-STAR, but could be just about anything including DMR or other digital modes. The board has a few refinements and additions over the original schematic supplied as BMP images. I never finished re-drawing the schematic with all of the changes, but the only significant additions are two LEDs for PTT status of analog and digital modes, JU4 and a relay for compatibility with other brands of repeaters. This board is not limited to use with DSTAR only. References to "DSTAR" can mean any digital mobile radio (digital voice) technology.

The MUX-25 pairs nicely with any RA from Masters Communications, and the STM32DVM from Scott Zimmerman - Repeater Builder - the company.

The MUX-25 has DB9 female connectors and is NOT intended to have the radio adapter directly connected by plugging the two boards directly into each other. This would require the DB9 on the MUX-25 to be male gender. Since interface cables are required no matter which series radio adapter you use, they need to be wired to align with the wiring scheme of the radio adapter you are using. The pinout of the DB9 on the DRA Series is different from the RA Series. If you intend on using a DRA with the MUX-25, the DB9 wiring is NOT straight through, like it is on the RA Series. The DRA will still work with the MUX-25, but the cabling will need to accommodate the different DB9 pinout of the DRA.

The current board revision (REV6) has no surface mounted components. The board includes a few additional features - jumper selectable power (JP4 - Red) for the Analog Port on Analog DB9 pin 9, and prioritization of the type of transmission (Analog or Digital). When installed, JP4 supplies 12V to Analog DB9 pin 9. Extra voltage is sometimes necessary when more audio is required to drive the radio/repeater transmitter. Power for the audio amplifiers on these radio interfaces can be optionally sourced from a the power supply of the MUX-25. This feature allows radio interfaces with audio amplifiers to be fed from the 12V supply powering the MUX-25 - by supplying that to pin 9 of the DB9. If you are using this feature with the RA or DRA with the LM386 amplifiers, select the "B" position for JU2 (the yellow jumper on the radio adapter). The DB9 on all RA-Series is pin for pin compatible with the MUX-25 - including this optional supply voltage. If you aren't using a RA or DRA Series product, or don't need voltage to power the amplifier in a DMK URI, just remove JP4 on the MUX-25.

Priority of transmission type is selected at the "JP" jumpers. This is detailed in the schematic diagram in the notes section.

Refer to page two of the schematic for jumper settings and additional notes on using transmitters with one modulator audio input. This board was intended to be used (primarily) with the Kenwood TKR-750/850 series repeater, but will work with other radios or repeaters (or even repeater controllers) if configured correctly as per page 2 of the PDF. If you have further questions on the operation of this circuitry, feel free to reach out to Ramesh - VA3UV. His email address is: ramesh (at) his callsign (dot) com.

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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 May 30, 2022, W3KKC All Rights Reserved!