If you’re exposed to ham radio for any length of time you are sure to hear some discussion of packet radio.
Without going into much detail, we’ll present a big-picture description here. Just enough for you to have a basic grasp of what’s involved and give you some idea of how it might apply to you.
Packet radio is a generalized term for a digital communication mode where data is sent in bite-sized chunks (packets) via radio. The transmission and receipt of packet data is largely automated and features data error correction for reliable messaging.
Packet radio (sometimes shortened to just packet) blends radio and computer technologies together. Sounds complicated but it really isn’t. All you need besides your normal ham radio transceiver is a household computer and an interface between the two. The heart of this interface is a Terminal Node Controller (TNC) which is an intelligent modem that converts text to audio tones and vice versa.
Reprinted with permission, 2013 Handbook; copyright ARRL
Packet radio can be used between hams directly in real-time (peer-to-peer or keyboard-to-keyboard) but is more commonly used to send messages that can be retrieved on demand. This operates more like email or mobile phone text messaging.
Slow data rates (typically 1200 baud) make large messages impractical, so packet messages should be relatively short and not have any large files attached. 120KB is the max message size accepted by some big message servers. A 4KB message will transfer in 2-2.5 minutes under ideal conditions at 1200 baud.
Particularly useful for emergency communication (EmComm) messages, packet radio is predominately used on VHF radios (more local) but can be sent over HF bands as well (for a larger incident covering a wider area).
Digipeaters are active packet radio systems that automatically relay or repeat packet radio transmissions to extend the range, just like voice repeaters. They are more commonly found in metropolitan areas but may be found in some remote areas as well, depending on how many hams are involved.
Multiple stations may transmit on a frequency simultaneously although things slow down or may stall when it gets crowded. As with other communication modes it is best to listen for activity before transmitting to minimize interference.
Assuming you already have a laptop or desktop computer and a VHF/UHF radio, you will need to buy or build a TNC and interface cables to your radio to start using packet radio. TNCs with cables will run in the $100-200 range so this is not too expensive. Besides the TNC you will need a software application to send and receive messages.
The most widely-used messaging system for EmComm is Winlink 2000. Winlink involves the internet for message storage and retrieval so unless the web goes down world-wide, it will be functional in most places. Packet radio can make up for the local or regional link to the internet (the “last mile”) with messages in case of a local or regional internet outage.
With multiple servers around the world and many gateway stations available, a ham stands an excellent chance of sending messages anywhere via radio. In addition to messages between licensed radio operators, emails can be exchanged between a ham and normal individuals or entities via Winlink.
As to the computer software (client) to manage the TNC and send/receive messages (or process peer-to-peer contacts) via Winlink, there are a few choices, most at no cost. EmComm users tend to favor RMS Express and Outpost. Be aware that there is little support for Mac PC software and limited availability of Linux clients so Winlink is mainly used by Windows-based PCs.
Handheld radios (HTs) can usually operate packet but have limited usability with their low power and inefficient antennas.
Here are some terms and definitions related to packet radio and the Winlink messaging system:
RMS= Radio Message Server– A “gateway” station, which bridges Winlink user radios to the email part of the internet.
RMS Express- Software used by Winlink users to interact with RMS stations; or to interact
with other user stations exchanging messages in the “peer to peer” fashion. Sometimes the abbreviation of RMSE is used when referring to RMS Express.
CMS- An email server associated with the Winlink system. Redundant locations are at San
Diego (California), Brentwood (Tennessee), Perth (Australia), Halifax (Canada), Wien
Winlink2000-(“Winlink” or “WL2K”). A system of email servers, radio stations, and
associated software. A private email system which supports Amateur Radio, MARS, and
SHARES users. It interacts with other email servers.
WINMOR – A cousin of packet, pactor, and Robust Packet.
Pactor – A cousin of packet, WINMOR, and Robust Packet. Siblings are Pactor 1
(slowest), Pactor 2, Pactor 3, Pactor 4 (fastest).
You are also likely to hear about Automatic Packet Reporting System (APRS). This is a specialized sub-set of packet radio and is worthy of a separate topic which we will present in the future.
To learn more, jump on the internet where you will find an abundance of information. Several recommended links are given below:
A great reference for packet radio is found here.
Excellent detail regarding Winlink is here.
Informative training for using Winlink via packet radio for EmComm is here.
WB9LOZ’s Introduction to Packet Radio found here.