Welcome to lesson 18. Ham radio continues to advance technologically and push the boundaries of what is possible with communications.
Over the last years and decades, ham radio innovators have created various digital modes of operation that allow you to encode information into digital signals.
Digital Modes
Digital modes can be used to send data, text, and emails, and can be so efficient that they transmit data around the world even when analog signals can’t get through.
There are many different digital modes, and talented ham radio operators can even create new ones. Packet radio, IEEE 802.11, and FT8 are all examples of digital communications modes. All of these choices are correct for examples of digital modes on the exam.
FT8
Perhaps the most popular digital mode right now is FT8, a digital mode capable of low signal-to-noise operation.
FT8 was invented by Joe Taylor, K1JT, an American astrophysicist and Nobel Prize winner who demonstrates the spirit of ham radio innovation, discovery, and technological advancement.
FT8 is usually operated using a computer program called WSJT-X.
WSJT-X Software Suite
WSJT-X also supports a variety of weak-signal activities that require extreme efficiency, such as:
- Earth-moon-earth, where you bounce your radio signal off the moon and back to another operator on Earth
- Weak signal propagation beacons, which allow you to receive real-time propagation info from beacon stations. This is commonly referred to as WSPR (“whisper”) for Weak Signal Propagation Reporter
- And meteor scatter, which allows you to communicate over hundreds of miles by bouncing radio signals off of the ionized trails left by meteors in the Earth’s atmosphere.
When asked which operating activities are supported by WSJT-X, all of these answers are correct.
PSK
PSK is a digital mode that stands for Phase Shift Keying. The keyword here is phase – unlike AM, which changes amplitude, or FM, which shifts the frequency, PSK shifts the phase of the carrier wave.
PSK, specifically PSK31, can be used for real-time, keyboard-to-keyboard chatting over ham radio.
DMR
DMR stands for digital mobile radio, and it is one of the most popular digital voice modes on VHF and UHF.
From a technical standpoint, DMR can be described as a technique for time-multiplexing two digital voice signals on a single 12.5 kHz repeater channel.
This means instead of one person taking up the entire frequency range, the frequency is divided into two time slots, and you can have two separate conversations on that frequency simultaneously.
Packet Radio & APRS
In addition to having conversations, ham radio also allows you to send packets of data over the radio waves.
This is called packet radio. One of the most popular uses of packet radio today is APRS, which stands for Automatic Packet Reporting System.
With APRS, you can transmit GPS position data, text messages, weather data, and more. All of these choices are correct when asked what data can be transmitted by APRS on the exam.
A real-world application of APRS is providing real-time tactical digital communications in conjunction with a map showing the locations of stations.
Check out this map of real-time station locations on APRS.fi as an example. This website collects the APRS packet transmissions with GPS coordinate data from ham radio stations and displays them on a real-time map.
FM or PM modulation is commonly used for VHF packet radio transmissions.
Error Detection & Correction
Packet radio uses a robust error detection and correction mechanism to ensure data is received reliably and accurately, which means even in a disaster where cell towers and fiber lines fail, packet radio provides a robust, independent way to move data over hundreds of miles.
Packet radio transmissions contain:
- A checksum that permits error detection
- A header that contains the call sign of the station to which the information is being sent
- An automatic repeat request in case of error
All of these choices are correct when asked what is included in packet radio transmissions on the exam.
The abbreviation for an automatic repeat request is ARQ, which is an error correction method in which the receiving station detects errors and sends a request for retransmission.
Essentially, it’s your station saying – “I didn’t receive that correctly – please send it again.”
Mesh Networking
Amateur radio operators can also combine multiple stations to form mesh networks.
An amateur radio mesh network is an amateur-radio data network using commercial Wi-Fi equipment with modified firmware.
The key phrase to remember here is Wi-Fi equipment with modified firmware – ham radio operators use off-the-shelf routers and modify them to use ham radio frequencies using specialized open-source firmware.
A ham radio mesh network is like a private, high-speed wireless network that doesn’t rely on the actual internet. They can be used for phone calls, texting, video feeds, file sharing, and more.
Linking Over the Internet
While amateur radio doesn’t rely on the internet, it is still possible to connect ham radio stations to the internet to extend your functionality.
An amateur radio station that connects other stations to the internet is called a gateway.
For example, ham radio operators can transmit their voice over the internet using Voice Over the Internet Protocol (VoIP).
VoIP is a method of delivering voice communications over the internet using digital techniques.
EchoLink
One implementation of VoIP is Echolink.
Echolink is a protocol that enables an amateur radio operator to transmit through a repeater without using a radio to initiate the transmission.
Here’s how it works. You download the Echolink software on your computer or smartphone, and you can instantly connect and talk on Echolink-enabled repeaters thousands of miles away over the internet.
Even though Echolink uses the internet, it still re-transmits your signals on amateur radio frequencies from the repeater, so before using Echolink, you must register your call sign and provide proof of license.
IRLP
Another implementation of VoIP is IRLP, the Internet Radio Linking Project.
The Internet Radio Linking Project (IRLP) is a technique to connect amateur radio systems, such as repeaters, via the internet.
IRLP is similar to Echolink, but unlike Echolink, you cannot use your computer to transmit – you have to transmit with a radio. Your signal is then received by the IRLP repeater or node, and is linked via the internet to other IRLP-connected repeaters or stations.
Access to IRLP nodes is accomplished by using Dual-Tone Multi-Frequency (DTMF) signals. DTMF is essentially the remote control for IRLP nodes.
Lesson Recap
Let’s recap. In this lesson, you learned about popular digital modes like
- FT8, a digital mode capable of low signal-to-noise operation
- PSK, phase shift keying used for real-time keyboard chatting
- And DMR, a technique for time-multiplexing two digital voice signals on a single 12.5 kHz repeater channel
We discussed packet radio, such as APRS, that can send GPS position data, text messages, and weather data, and display real-time station positions on a map.
Finally, we discussed linking ham radio over the internet using a gateway, such as EchoLink, which allows you to communicate on repeaters using computer software, and IRLP, which uses DTMF signals to access nodes.
