Packet

Packet, or AX.25

The Rundown

Basically, Packet is a way of using radios to connect to a de-centralized, alternative "internet" for communications. There are message board, chat, and email functionalities provided by packet routers, and packet modems are what enable you to talk to those routers. By linking in with repeater systems, you can still connect and communicate with systems that are father away.

AX25 details

Info on using Baofeng UV5R to do packet or AX25:

https://www.reddit.com/r/amateurradio/comments/1a5c6f/baofeng_uv5r_and_psk31_interfacing_with_laptop/

To make a sound modem to do AX25 with a handheld radio, you need two paths for audio:

• output of soundcard goes to radio mic
• output/speaker of radio goes to soundcard mic
• audio transformers needed to match impedance between these
• PTT - if something is plugged into the combination headphone/mic jack, PTT will engage the button if the mic is on
• You can add an optoisolator - connected to the radio mic connection - and a serial port interface
• USB serial adapter that has a real RTS or CTS signal

How many parts? two or three parts, depending on how you do transformers. Bunch of audio cables, proper USB-serial adapter, serial connector to fit adapter (so you have something to solder on to), but an FTDI cable could have pinouts.

Most popular one is Singal Link USB - making your own is cheap and fun.

Can use VHF/UHF for APRS and Packet BBS on 2 meters. PSK will only be on SSB on HF. Would require upverters. Circuit could interface with other HF-capable radios.

Links

Introduction: http://www.m0spn.co.uk/2016/01/10/introduction-to-packet-ax-25/

TNC modem for Packet via Raspberry Pi: http://www.tnc-x.com/TNCPi.htm

Nice writeup of using a Baofeng UV-3R for packet. TLDR: Baofeng had some issues. Icom worked better.