In our previous discussions, we walked through the process of taking an organized frequency list from Excel or Google Sheets and “deploying” it to your handheld radio using CHIRP. By now, you should be comfortable with the “Read-Import-Write” workflow—always downloading the factory config from your radio first to create a baseline before importing your custom CSV.
But once your radio is programmed and you start scanning, you will eventually land on a channel that sounds like rhythmic buzzing or data “hiss” instead of a human voice.
My curiosity was piqued the moment I realized that amateur radio wasn’t just about legacy voice transmissions, but about a vast, interconnected digital landscape. This sparked a deep dive into how we can leverage radio as a transport layer for complex data—moving beyond the hardware to explore the protocols themselves. Today, we’re going to look at what I’ve discovered in these two main digital branches: Digital Voice and Digital Data."
Digital Voice (DV): Networking Your Speech
Digital Voice takes your analog voice, runs it through a hardware “encoder” to digitize it, and sends it as a stream of 1s and 0s. This eliminates the static found in other FM broadcasts (you either have a perfect signal, or you have nothing the “cliff effect”).
The Major Players:
DMR (Digital Mobile Radio): Originally a commercial standard, DMR uses Time Division Multiple Access (TDMA). It splits a frequency into two Time Slots, effectively doubling the capacity. It relies on Talk Groups to route audio globally.
D-Star: Championed by Icom, this was the first major digital mode built specifically for hams. It’s highly regarded for its ability to route calls directly to a specific user’s callsign.
System Fusion (C4FM): Yaesu’s take on digital. It’s the most user-friendly because of its “Automatic Mode Select” (AMS), which allows the radio to switch between analog FM and digital C4FM on the fly.
AllStar Link: Unlike the others, AllStar is a Linux-based system built on Asterisk (the open-source PBX). It links analog repeaters via the internet using high-quality VoIP-style audio.
The Internet Bridge: Repeaters & Hotspots
Digital Voice is powerful because it’s networked. Many repeaters are linked via the internet, allowing a low-power handheld in Texas to talk to a station in Japan. If you aren’t near a digital repeater, you can use a Hotspot—a tiny personal gateway connected to your home Wi-Fi—to bridge your radio to these global networks.
How Repeater Linking Works: The “IP Gateway”
When you key up on a digital repeater (DMR, D-Star, or System Fusion), your radio doesn’t just broadcast an RF signal. It sends a packetized data stream that includes your digitized voice, your callsign, and a destination “Talk Group” or “Reflector” ID.
The repeater receives this RF signal and hands it off to an on-site Gateway—typically a computer or specialized controller connected to the internet. This gateway sends your data packets to a central Master Server (like the BrandMeister network for DMR or the US Trust for D-Star). That server then looks at which other repeaters around the world are currently “subscribed” to your Talk Group and pushes your voice data to them simultaneously.
The result? You can stand in a park with a 5-watt handheld and, within milliseconds, be heard on hundreds of repeaters across multiple continents with zero signal degradation.
The Personal Gateway: Digital Voice Hotspots
If you live in a “dead zone” or simply want more control over which networks you access, you need a Hotspot. Think of this as your own private, micro-power digital repeater. It receives the low-power RF signal from your HT and bridges it directly to the internet.
Popular Off-the-Shelf Options
If you want a “plug-and-play” experience with high-quality hardware, there are two dominant leaders in the market:
SharkRF openSPOT (v4 Pro): Often considered the “Gold Standard” for ease of use. It is a standalone device—it doesn’t require a Raspberry Pi. It is famous for its “Cross-Mode” capabilities, allowing you to use a DMR radio to talk on System Fusion networks, or vice-versa.
BridgeCom SkyBridge: A very popular “ready to run” option, especially for DMR users. It typically comes pre-configured and uses a dual-band design so you can monitor two different digital frequencies at once.
The “Maker” Approach: Building Your Own
For those of us who enjoy the “homelab” aspect of the hobby, building your own hotspot is incredibly rewarding and cost-effective.
The Brains: You’ll need a Raspberry Pi. While a Pi 4 or 5 works, a Raspberry Pi Zero 2 W is the preferred choice due to its tiny footprint and low power consumption—perfect for a pocket-sized hotspot.
The Radio Hat: You need an MMDVM (Multi-Mode Digital Voice Modem) Hat. This is a small board that sits on top of the Pi’s GPIO pins. It contains the tiny transceiver that talks to your handheld radio.
The OS: Most builders use Pi-Star or the newer WPSD (Wireless Packet Software Dashboard). These are specialized Linux distributions that provide a web-based dashboard to manage your frequencies, Talk Groups, and network connections.
Why the Maker Route?
Building your own hotspot with a Raspberry Pi gives you a transparent look at the underlying protocols. You can SSH into the device, view the logs in real-time, and truly understand how your voice is being packetized and routed. It turns a “black box” appliance into a visible, manageable node in your personal network.
Digital Data: The Foundation of Modern Networking
Digital Data modes are different. You aren’t talking; your computer (or a dedicated internal modem) is “singing” into the radio’s audio input to send text, files, or telemetry.
A History of Innovation
Long before the public internet, hams were building Packet Radio networks using the AX.25 protocol. This was the experimental playground for the protocols we take for granted today. In fact, many early networking concepts—like packet encapsulation and error-correction—served as the templates for what eventually became the TCP/IP stack. We were routing data through “digipeaters” decades before Wi-Fi existed.
Popular Modern Modes
RTTY (Radio Teletype): One of the oldest digital modes in existence, RTTY uses Frequency Shift Keying (FSK) to transmit text. It was originally designed to drive mechanical teleprinters and remains a staple in amateur radio contesting and DXing due to its historical significance and ability to cut through noise better than traditional analog voice.
FT8: A weak-signal powerhouse. It can pull data out of the noise that no human ear could ever hear. It’s the ultimate tool for testing antenna performance and propagation.
JS8Call: Built on the FT8 skeleton, this mode allows for keyboard-to-keyboard messaging, providing a reliable way to chat even when the bands are nearly dead.
Sending Morse Code over the airwaves via Continuous Wave (CW) could qualify as a “digital” mode by its definition. This is one of the most enduring debates in the shack. From a technical architecture standpoint, CW is the original binary protocol: the carrier wave is either “on” or “off” (1 or 0), making it structurally digital by definition. Long before we had the processing power for complex encoders, hams were using this high-efficiency, low-bandwidth “pulse” to bridge continents. However, in modern amateur radio parlance, “Digital Modes” usually refers to signals that require a computer or a DSP chip to encode and decode the data. Since the human brain remains the most effective “sound card” for translating those rhythmic dits and dahs into meaning, many purists categorize it as a manual mode. Ultimately, CW exists in a fascinating grey area—it is a minimalist digital transmission that relies on analog human intuition to complete the circuit.
APRS: The “Location API” of the Airwaves
A special mention must go to APRS (Automatic Packet Reporting System). While it is a data mode, it serves a unique role in the hobby.
APRS is used for real-time tactical communication. It allows hams to transmit their GPS coordinates, weather station data, and short text messages. It’s the “Find My Friends” of ham radio, and it’s invaluable for search and rescue or public service events. It’s a distributed, ad-hoc network that doesn’t rely on cell towers to keep people connected.
Why Are These Modes Popular Today?
The surge in digital mode popularity comes down to efficiency and community.
Noise Floor: As urban environments get noisier, digital modes like FT8 allow us to communicate where analog would fail.
Global Reach: Internet-linked digital voice modes (DMR/Fusion) have removed the barrier of entry for local Technicians to have global conversations.
The Tech-Radio Convergence: For those of us with a tech background, these modes allow us to apply our knowledge of networking, Linux, and data structures to a 100-year-old hobby.
Most modern radios now come standard with digital connections allowing for a direct connection from the radio into a computer
Whether you are configuring a DMR codeplug or timing an FT8 sequence, you aren’t just an operator—you’re a network architect of the airwaves.
73,
Chris - K5CTW The Ham Radio Lab