USB Radio Adapter
For Two-Way Radio Applications
Model RA-35 REV2
Top side of RA-35 board - shown slightly enlarged.
(Click photo to show a very large image)
Bottom side of RA-35 board - shown slightly enlarged.
(Click photo to show a very large image)
Schematic Image - Click to download a high quality PDF.
Overview of the latest changes in REV2:
1, EEPROM is now supplied on all kits and assembled and tested units.
2, Access to all GPIO from circuit board 'lands' marked G1 through G8.
3, Bias resistors for Q1 and Q3 - see below.
4, PSEL option (preconfigured for a ground - see below).
5, VSEL option (preconfigured for an open - see below).
6, Kits come with the surface-mount ICs preinstalled.
The PSEL and VSEL options are only required for proper operation of the CM119 (without the A suffix) or the CM108. All REV2 boards are shipped with CM119A chips, and PSEL and VSEL are preconfigured for normal operation and won't require any jumpers or other attention.
Q1 and Q3 are now 2N2222 bipolar transistors. The prototype used FETs in these locations but I felt the bipolar was a better fit. The FETs didn't require bias resistors and is why R22 and R23 were added to the REV2 circuit board to accommodate the 2N2222.
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 photo.
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-35 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 REV2 production boards are supplied with a Genuine C-Media CM119A. REV2 boards are plainly marked "REV2" on the solder side (EEPROM side) of the PC board.
The REV2 board was designed to be versatile. Some Prototype RA-35s used a CM119 while most were supplied with a CM119A. A CM108 is also acceptable. 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-35 to a Kenwood TKR-750/850 repeater.
Click here for programing recommendations and wiring/hook-up instructions.
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Custom cables available from URI Cables. They will build a custom cable for the RA-35 for many radios.
Custer for support, ordering information, order by check, and/or quantity pricing of this
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 November 27, 2016, W3KKC All Rights Reserved!