Custom Products for the Repeater Builder

USB Radio Adapter Interface Board
For Two-Way Radio Applications

Model RA-40 REV1

Top side of RA-40 board - shown slightly enlarged.
(Click photo to show a larger image)

Bottom side of RA-40 board - shown slightly enlarged.
(Click photo to show a larger image)

Schematic Image - Click to download a high quality PDF.

Overview of the differences between the RA-35 and RA-40:

The RA-35, as designed, has LOTS of transmit audio, and in some instances too much. If your radio tune TX settings end up below 100, it's probably best to do something to cut the audio down. Depending on what you are driving, the RA-35 may need to 'reconfigured' to work in an optimal way. Older radios like the MASTR II, MICOR, and Kenwood TKR series interface well as supplied/designed. Many folks are using the RA-35 with the System Fusion repeater because it requires lots of transmit audio.

Other radios like the Kenwood TM-V71A, Radius, Maxtrac, and GM-300's don't require a lot of TX audio. This makes it difficult to set the TX audio level correctly, because when you get below 100 or so with the "radio tune txvoice" command it gets pretty granular. At low settings, these large steps between tune values makes it difficult to set the audio levels precisely. Even at TX tune settings of 50 or so, MIC inputs can be over-driven resulting in distorted TX audio.

Circuitry wise, the RA-40 identical to the RA-35 with one exception, it includes two more pots (on the main board) for coarsely controlling the main/aux - left/right TX audio. These pots do the same thing as the volume boards do for the RA-35, but also allows the installation of the optional filters - if desired.
Kits come with the surface-mount ICs preinstalled.

If you purchased our kit, refer to the parts list and make sure you have all of the components you need to build it.
Click here for Parts List.

Click here for assembly instructions and construction notes - with large photos.

This device is intended to be installed inside a radio, computer, or project box for protection. Refer to the schematic for the pinout of the DB9F where all of the logic signals, power connections, and audio signals are listed.
Click here for DB9, jumpers and other board connection assignments.

H1 and H2 header pin assignments:
Click here
for a detailed header pin explanation. The primary purpose of the headers H1 and H2 are for installation of optional FL-10 audio filters. The FL-10 is designed to be installed onto the header pins directly or remotely by extending the four pins with wires. Jumpers are needed over the center two pins if the optional filters are not installed.

Recommended powering requirements:
The board is supplied with 5 VDC from the USB connection. The audio amplifiers and optional filters can run from this, or from an external power source of 6 to 15 VDC. Jumper JU2 controls where the voltage is sourced from.

Recommended discriminator audio input level:
The RA-40 accepts the widest range of audio compared to any other similar radio adapter. The input signal is attenuated by a potentiometer, giving the broadest range of acceptable levels. As little as 20 mV P-P can be used with a setting of rxboost=1, and as much as 20 volts P-P with a setting of rxboost=0. If your discriminator level is adjustable or programmable (like in a Kenwood TKR-750), we recommend around 2.0 volts P-P and a rxboost=0 setting. This allows very good signal-to-noise ratio and low cabling cross talk. This level results in a 50% rotational setting of the potentiometer.

Which C-Media chipset is used?
All RA-40's are supplied with a Genuine C-Media CM119A, but the RA-40 board was designed to be versatile. It will accept a CM119 (without the A) and even the CM108. There are slight differences between these components, and the board can be 'programmed' to accept any of the three.

Information on the CM119A.
Click here
to download a manual for the C-Media CM119A.

Information on the CM119.
Click here
to download a manual for the C-Media CM119.

Information on interfacing the RA-40 to a Kenwood TKR-750/850 repeater.
Click here
for programing recommendations and wiring/hook-up instructions.

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Kit or Assembled & Tested?

Custom cables available from URI Cables. They will build a custom cable for the RA-40 for many radios.

Third Party Compatible Projects:
MABEL is an interface and software that allows analog control of the Yaesu DR-1X repeater and access to the AllStar VOIP network with the Raspberry Pi3 and AllStar Asterisk. (Offsite Link)

Email Kevin Custer for support, ordering information, order by check, and/or quantity pricing of this exciting product.

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 13, 2017, W3KKC All Rights Reserved!