SCCo ARES/RACES Network: AX.25 over VHF Amateur Radio

Overview

AX.25 is a protocol based on the X.25 protocol and uses amateur radio call signs for addresses. It is efficient for low bandwidth, lossy environments, such as VHF/UHF radio. This makes it ideal for access to the packet BBS network from anywhere in Santa Clara County. The use of VHF radio means RF coverage throughout the county is good enough for most locations to reach at least two of the packet BBS systems.

Accessible Services

AX.25 over VHF Amateur Radio can be used to access the following SCCo ARES/RACES service:

Packet BBS Service
- User Access: Users can connect to the packet BBSs using one of the VHF radio channels allocated for user access.
- BBS Forwarding: Other packet BBSs can connect to the SCCo BBS network using AX.25 on a radio channel allocated for BBS Forwarding..

How To Connect

User Access

No advanced arrangements are necessary to connect to the SCCo ARES/RACES packet BBS service via VHF radio
Construct a packet station (see below)
Consult the Packet Frequencies and BBS Listings page to determine which BBS you should use and the access frequencies for that BBS
Consult the Packet BBS Service page for complete information about using the service

BBS Forwarding

Consult the Packet Frequencies and BBS Listings page to determine the BBS forwarding frequencies to use
Make a test connection to verify reachability
Contact one of the SCCo BBS sysops directly to set up forwarding

Equipment and Software

AX.25 over VHF Station Configuration Diagram (PDF)
Consider the following when building an AX.25 (packet) over VHF radio station:
- City/Agency EOC/DOC Equipment
- Antenna
- Feedline
- Lightning Arrestor
- Radio
- TNC
- USB-to-Serial Adapter
- Computer
- Printer
- Software
- Network
- Power
- Make sure your station helps to reduce/eliminate the "hidden node" problem

Resources

Application Notes

Configuration and Setup Instructions

Standard TNC Parameter Settings - 04/07/2016 (PDF - 509 KB)
Setting Your TNC's Audio Drive Level
- This is an excellent tutorial on FM deviation for packet, why it's important, and how to set it.
- Skip to "The No-Test-Equipment Packet Adjustment System" for a method to set 1200 baud deviation by ear. The result will be very close to ideal.
- If you have trouble hearing the difference between audio levels, you can use a simple audio dB meter located near the speaker, such as an app on your smartphone.

Technical Reference

AX.25 Protocol Specification
- AX.25 Link Access Protocol for Amateur Packet Radio, Version 2.2, Revision: July 1998

Support

Training

Santa Clara County ARES/RACES Packet Training Classes
Covers everything from assembling and using an existing station up through building your own station and using advanced BBS features.

User Group

A discussion/e-mail group is available for SCCo ARES/RACES members interested in packet networking.

To Join: Visit our Discussion Groups page to learn how to subscribe to our main Announce group. Once approved, you can subscribe to the Packet group.

Technical Support

How to Request Packet Networking Technical Support

Network Access using AX.25 over VHF Amateur Radio