APRS Messaging: How to Send Text Messages, Email, and More
By ERIC HENDRICKSON
Welcome to Part 2 of our exploration of APRS. In Part 1, we covered the fundamentals of APRS, how to set up a station, and took a cursory look at how paths works and how messages get distributed. Now, let’s take a look at a powerful but often underutilized feature: APRS messaging and gateway services.
While APRS is known for and used primarily for position reporting, it is also a robust digital messaging network. With the right approach, APRS can facilitate direct user-to-user communications, send SMS text messages, relay emails, and integrate with Winlink Global Radio Email. I will explore these messaging types and explain exactly how to compose, send, and receive messages using each method. It’s up to you to figure out how these features are implemented in your specific radio.
Some radios make it much easier than others to compose and send a text message using a DTMF pad on a microphone or a makeshift on-screen keyboard. Both are cumbersome to use but they get the job done.
Direct User-to-User APRS Messaging
Direct station-to-station APRS messaging allows hams to send short text messages to each other over RF. Unlike traditional voice QSOs, this form of communication is discrete, efficient, and can be useful in emergencies, or when voice isn’t practical. Direct APRS messages are just that: A message addressed to a specific recipient. It’s worth noting that direct message may traverse one or more digipeaters in the process. Direct APRS messaging is the simplest form of station-to-station communication with APRS. There are no gateways or service providers required.
How to Use Direct APRS Messaging
- Address your message: Similar to other messaging apps, you should see a “TO” field in your radio or application. Make sure to address your message to the recipient’s full call sign including SSID (i.e.: W6HS-9).
- Compose the message: APRS messages are limited to 67 characters, so keep it concise.
- Use your radio or software to send: Depending on your setup, use the messaging function of your APRS-capable radio or a software client like Pinpoint APRS.
👉 See my separate article on Using PinPoint APRS with APRS-IS. - Transmit via RF: Ensure your recipient is in range, double check your message addressing and content, then hit send.
- Wait for an acknowledgment: If the recipient receives the message, their station should automatically send an acknowledgement back. If no “ACK” is received, the message may need to be sent again.
Practical Use Cases for Direct APRS Messaging
- Coordinating with other operators during an event.
- Sending tactical messages when voice channels are crowded.
- Sending information where precision and detail is important.
- Testing APRS station connectivity.
APRS SMS Gateway
The APRS SMS gateway allows APRS users to interact with the cellular network by sending text messages to cellphones and allows cell phone users to respond back to the APRS network.
How to Send Text Message with APRS
- Format the message:
- Address the message to
SMS. - The message should begin with the recipient’s phone number, followed by a space, then the message content.
- Example:
1234567890 Testing APRS SMS!
- Address the message to
- Transmit the message: Use your APRS radio or software to send it.
- Gateway forwards the message: The APRS network routes the message through an IGate to an internet-connected SMS gateway, which then forwards it to the cellphone number provided.
- Recipient receives the text: The SMS will show as originating from the SMS gateway. The message will show up on their device from the gateway’s phone number.
Receiving Replies from SMS Users
- Non-ham recipients must opt-in before receiving or replying to messages. They must send an initial text confirming they wish to receive APRS messages. This is to comply with anti-spam and control operator regulations.
- Once opted in, messages can be received from APRS and replies can be sent by texting back to the number provided in the SMS (a temporary gateway number).
- When it receives an SMS response, the gateway server sends it back through APRS-IS with specific routing information that will hopefully be seen by the digipeater or igate that originally heard the RF to SMS message and sent the request. If that machine see the response on APRS-IS, it will digipeat the message over the air. Keep in mind not all digipeaters and igates support this type of two-way interaction with APRS-IS and the SMS gateways.
- Ensure your station remains active to receive replies and acknowledgements.
Practical Use Cases for APRS Messaging with SMS
- Contacting family or friends when out of cellular coverage.
- Emergency communications when cellular services are down.
- Everyday personal use in areas where cellular coverage is spotty.
APRS Email Gateway
In addition to SMS, APRS users can also send short emails, making it an excellent tool for emergency use or when no other internet connection is available.
How to Send Email with APRS
- Format the message:
- Address the message to
EMAIL(The word EMAIL goes in the TO field). - The first word in the message should be the recipient’s email address, followed by a space, then your message.
- Example:
email@example.com This is an APRS email test.
- Address the message to
- Transmit via APRS: Just like with SMS, your APRS client or radio will send the message.
- Email Gateway processes the message: The APRS system forwards the message to an email gateway, which then hands it off to email relays on the internet for delivery to the intended email recipient.
- Recipient receives the email: The email will indicate that it originated from an APRS station. Responding to an email sent from an APRS user is not as easy and depends on the gateway and digipeater/igate system. As with SMS, not all digipeaters or igates will process and handle response messages.
Receiving Replies from Email
- In most cases, replies are not automatically forwarded back to APRS.
- Email replies are not well supported in all areas.
- Most APRS-to-email gateways are one-way: APRS in; email out.
Practical Use Cases for Sending Email with APRS
- Sending short emergency messages via APRS when no other email access is available.
- Notifying a contact about your APRS status.
- Simple off-grid email capabilities.
APRS Messaging Using Winlink Gateway
For those who need more advanced email capabilities, APRS can interface with Winlink, allowing access to a global email network from an APRS capable radio.
How to Send Email with Winlink
- Format the message:
- Address it to
WLNK-1. - The first line should be
SP recipient@domain.com(SP stands for “send position”). - Follow it with the email body, keeping within character limits.
- Example:
SP callsign@winlink.org Testing APRS Winlink.
- Address it to
- Transmit via APRS: Your message will be forwarded through IGates.
- Winlink processes the message: It converts your APRS packet into an email and sends it via Winlink’s email servers.
Receiving Replies from Winlink
- Replies are typically retrieved via Winlink clients (e.g., Winlink Express, Pat).
- Winlink email can also forward incoming emails as APRS messages if configured.
Practical Use Cases for using Winlink with APRS
- Long-range email capabilities via APRS.
- Emergency preparedness when operating in the field.
- Accessing global email networks from an APRS-enabled radio.
APRS Messaging in Practice
APRS messaging extends far beyond simple position reports. By leveraging these messaging techniques, you can enhance your ability to communicate when traditional methods fail. Each of these methods—direct messaging, SMS, email, and Winlink—has practical applications, whether for routine use, emergency communications, or experimentation.
The best way to become proficient is to practice. Try sending APRS messages to a friend, test out SMS and email gateways, and explore Winlink integration. APRS is more than just a beaconing system; it’s a versatile digital messaging platform that every ham should be familiar with. Organize a local APRS net. Get some friends together and exchange APRS messages using the various methods described here. Make it fun so others will want to join in.
Stay tuned for Part 3, where we’ll explore APRS path settings further and introduce the WIDE path setting and how it can be used to augment coverage in remote locations.
Full path: https://w6hs.net/aprs-messaging-how-to-send-text-messages-email-and-more/
Shortcut: https://w6hs.net/r/aprs2
