NX5000 Interfacing

This page is a collection of useful info regarding interfacing with the Kenwood NX5000 series mobiles.

Rear DB25 Port (Mobiles)

Below is the pinout for the NX5700/5800/5900 rear DB25 connector. This was pulled directly from the Kenwood service manual.

Combination APRS & VRS Audio System

While working on my mobile installation, I found a need to use my VHF NX5700 brick for APRS packet transmissions, in addition to its existing use as my main VHF P25/DMR radio. I also had a VRS system installed and interfacing with a Pyramid SVR200, so I'd need to handle multiple audio and PTT sources in addition to channel steering to make sure APRS stayed on 144.390. As it turns out, this is all possible thanks to the fantastic extended configuration options provided with the NX5000 line.

The Overview

First, an illustration of all the system components and their functions:

• The NX5700 is, well, an NX5700. It's a VHF Analog/P25/DMR radio from Kenwood and it's great. You should get one.
• The SVR200 is a UHF vehicular repeater that transmits on a simplex frequency at around 5W, and passes transmit and receive audio to and from the NX5700 on whatever channel the radio is tuned to.
• The APRS TNC is a custom design which is based on an CM108 USB audio chip, and handles PTT and audio for APRS data. In this configuration, the modem is used for transmit only, as APRS RX duties are handled by an RTL-SDR connected to a separate antenna on the vehicle.

In addition to keying the radio, the APRS modem must also steer the radio to the proper APRS channel (in my case, 144.390), and revert back to the previous channel once the message has been sent. This can be accomplished using the Channel Select A-D GPIO functions available on the NX5700.

The Challenge

If only the SVR200 was being used, I could easily just follow Pyramid's application notes for the NX5000 series mobiles and everything would be peachy. The addition of an APRS modem throws a wrench into the whole plan, as I need a shared PTT line for both the SVR and modem, but I need to isolate the channel steering to the APRS modem by itself.