VHF/UHF Digital Ham Radio

D-STAR

Digital Smart Technology for Amateur Radio (D-STAR) was the first VHF/UHF digital mode deployed for amateur use in the Richmond area, in 2008.  D-STAR radios are manufactured by Icom and Kenwood.  It supports a single channel of digital voice or low-speed data.  "High speed" IP data (up to 128 kbps) is also possible at 1.2 GHz.

►  Manufacturers:  Icom, Kenwood
►  Commercial branding:  D-STAR.  Only offered as amateur product.
►  Channel bandwidth, modulation:  6.25 kHz FDMA
►  Hotspots:  Yes, the "original" hotspot mode -- widely supported

Local repeaters:

►  W4FJ 147.255(+) Richmond - Digital voice/low speed data, FM PL 74.4
►  W4FJ 443.7125(+) Richmond - Digital voice/low speed data, FM PL 74.4
►  W4FJ 1284.0000(-) Richmond - Digital voice/low speed data, FM PL 74.4

Richmond's D-STAR repeaters are operated by the Richmond Amateur Radio Club.

To learn more:

►  Richmond Amateur Radio Club:  Repeaters
►  Richmond Amateur Radio Club: W4FJ D-STAR Gateway
►  dstarinfo.com
►  W7GH's D-STAR Quick Start Guide

C4FM

Continuous Four-Level Frequency Modulation (C4FM) uses 4FSK modulation to transmit clearer, more reliable voice and data in weak-signal conditions.  Like D-STAR, C4FM was designed specifically for amateur radio use.  Most C4FM repeaters also support FM operation, but linking (WIRES-X, IMRS) requires digital.

►  Manufacturers:  Yaesu
►  Commercial branding:  Yaesu System Fusion™. Amateur products only.
►  Channel bandwidth, modulation:  12.5 kHz FDMA, 4FSK
►  Hotspots:  Widely supported. No access to IMRS. Limited WIRES-X access.

Local repeaters:

►  W4RAT 146.8800(-) Richmond - DG-ID 00 WIRES-X; FM PL 74.4 (RATS)
►  W4RAT 442.5500(+) Richmond - DG-ID 00, AMS in=FM out, PL 74.4 (RATS)
►  N4POW 147.3150(+) Powhatan - DG-ID 00 WIRES-X; FM PL 74.4 (PARC)
►  N4VEM 146.9400(-) Richmond - DG-ID 00, FM PL 74.4 (ARCA)
►  KG4MRA 145.4300(-) Richmond - DG-ID 00, AMS in=FM out, PL 74.4 (MRA)
►  KD4RJN 147.0600(+) Beaverdam - DG-ID 00, FM PL 74.4

To learn more:

►  Yaesu:  What is System Fusion?
►  Yaesu:  WIRES-X

DMR

Digital Mobile Radio (DMR) is an ETSI standard technology designed for commercial, professional, and public safety users, offering improved spectral efficiency (two simultaneous voice channels in a single 12.5 kHz bandwidth), enhanced audio quality, integrated IP data capabilities, and messaging.

►  Manufacturers:  Many dozens to choose from
►  Commercial branding:  Motorola TRBO™
►  Channel bandwidth, modulation:  12.5 kHz 2-slot TDMA
►  Hotspots:  Yes, but no direct connectivity to C-Bridge based networks

Local repeaters:

►  W4RAT 443.5875(+) Richmond - CC1 (RATS)
►  WA4FC 444.6125(+) Beaverdam - CC1 (Fieldcomm/DMRVA)
►  WA4FC 443.4375(+) Goochland - CC1 (Fieldcomm/DMRVA)
►  WA4FC 442.0500(+) New Kent - CC1 (Fieldcomm/DMRVA)
►  WA4FC 442.6875(+) Petersburg - CC1 (Fieldcomm/DMRVA)
►  N4POW 443.3500(+) Powhatan - CC1 (PARC)

All repeaters listed here are part of the combined DMRVA+HEARS C-Bridge network.

To learn more:

►  DMRVA
►  RATS:  DMR FAQ
►  RATS DMR Codeplug Project
►  RATS DMR Codeplug Project:  FAQ

P25

Project 25 (P25) encompasses several radio standards developed by APCO primarily to ensure interoperability among public safety agencies -- police, fire, and emergency services -- across jurisdictions and equipment brands.  It is the dominant technology used by land-mobile public safety radio systems in the US.

►  Manufacturers:  Icom, Kenwood
►  Commercial branding:  Motorola ASTRO, Harris VIDA, Kenwood ATLAS, others
►  Channel bandwidth, modulation:  12.5 kHz; Phase 1: FDMA; Phase 2: 2xTDMA
►  Hotspots:  Limited support

Local repeaters:

►  WA4FC 927.0500(-) Richmond - NAC $293, FM PL 100.0 (Fieldcomm)
►  W4CUL 147.1200(+) Gordonsville - NAC $293, FM PL 146.2 (CARA)
►  W4CUL 443.8000(+) Gordonsville - NAC $293, FM PL 146.2, C4FM DG-ID 00

To learn more:

►  Fieldcomm Association: 927.05 MHz Repeater
►  Hanover Virginia Amateur Radio Club
►  Culpeper Amateur Radio Association

NXDN

Next Generation Digital Narrowband (NXDN) was developed jointly by Icom and Kenwood.  Its 6.25 kHz channel width allows for twice as many voice channels compared to conventional FM.  It supports digital voice, messaging, and GPS.  Among hams, this is one of the least popular of the modes listed on this page.

►  Manufacturers:  Icom, Kenwood
►  Commercial branding:  Kenwood NEXEDGE™
►  Channel bandwidth, modulation: 6.25 or 12.5 kHz FDMA
►  Hotspots:  Limited support

Local repeaters:

►  There are no known NXDN repeaters in the Richmond area at this time.

To learn more:

►  NXDNINFO.com
►  groups.io:  KenwoodNXDN

M17

Module 17 (M17) is a fully open-source digital protocol developed by the amateur community since 2019, designed as an alternative to commercial products like D-STAR, DMR, C4FM, etc.  It supports digital voice, IP data, messaging, and other features, and involves no licensing fees for the underlying technologies.

►  Manufacturers:  Connect Systems
►  Commercial branding:  None.  Only offered as amateur product.
►  Channel bandwidth, modulation: 9 kHz FDMA, 4FSK
►  Hotspots:  Yes -- new technology, confirm support w/hotspot manufacturer

Local repeaters:

►  There are no known M17 repeaters in the Richmond area at this time.

To learn more:

►  M17 Project Website
►  groups.io:  M17-Users
►  A note about M17 support in MMDVM

Packet, Winlink

Packet Radio is one of amateur radio’s earliest digital data modes, dating to the late 1970s and standardized in the 1980s using the AX.25 protocol, a derivative of the X.25 networking standard. It transmits bursts of digital data -- typically at 1200 baud on 2m and 9600 at 70cm -- allowing stations to exchange messages, telemetry, or even route packets through digipeaters to form ad hoc radio networks.

Winlink over VHF Packet builds on this foundation by using packet radio as the transport layer for the Winlink Global Messaging System, enabling users to send and receive email-like messages entirely over RF when Internet or cellular infrastructure is unavailable. Stations connect via packet modems (TNCs) to local RMS (Radio Message Server) gateways, which forward mail through the broader Winlink network when connected, or directly between peers when off-grid. Together, VHF Packet and Winlink Packet provide a robust, low-bandwidth, store-and-forward data path widely used in emergency communications and field operations.

For more information:

►  Catastrophic Amateur Tactical Squad (KC4TS)
►  Virginia Packet Network (VAPN)
►  Virginia Digital Emergency Network (VDEN)
►  Winlink

APRS

Automatic Packet Reporting System (APRS) was created by Bob Bruninga WB4APR (SK) in the late 1980s to enable live information sharing among amateur radio operators.  It exists primarily on 144.390 MHz using 1200 baud VHF packet.

APRS supports not only GPS-based position reporting but also two-way text messaging, weather telemetry, and the exchange of objects and bulletins. Stations relay packets through digipeaters and iGates, which bridge radio traffic to the Internet for global visibility via platforms like aprs.fi. Far more than just vehicle tracking, APRS functions as a real-time messaging and situational awareness network, widely used in public service events, emergency response, and day-to-day communication between stations worldwide.

Several manufacturers of handheld transceivers (HTs) offer built-in APRS functionality such as position beacons and two-way messaging.  APRS over HF is also a thing, and UHF APRS networks exist in some areas.

For more information:

►  RATS APRS History
►  APRS.org  (archived legacy content)
►  how.aprs.works
►  aprs.fi

VARA-FM

VARA-FM is a modern, high-speed digital soundcard modem developed by José Alberto Nieto Ros, EA5HVK, to provide efficient data transfer over analog FM radio channels. Operating on standard 25 kHz or narrow 12.5 kHz FM channels, VARA-FM uses advanced OFDM modulation and robust forward error correction to achieve throughput up to several kilobits per second, far faster and more reliable than traditional packet radio.  It works entirely in software, using a computer and soundcard or radio interface, and is compatible with most FM transceivers used in the VHF and UHF amateur bands.

When used with Winlink, VARA-FM serves as the transport layer for sending and receiving email-like messages entirely over RF. Stations connect through Winlink RMS gateways that support the VARA-FM protocol, achieving fast, automatic, error-corrected data exchange with minimal configuration. This combination has become one of the most popular methods for high-speed local and regional Winlink operation, offering performance comparable to HF VARA but optimized for line-of-sight VHF/UHF links commonly used in emergency communications and field operations.

For more information:

►  Catastrophic Amateur Tactical Squad (KC4TS)
►  Virginia Digital Emergency Network (VDEN)
►  VARA-HF, VARA-FM, VARA-SAT and other VARA applications
►  Winlink

NPR-70

New Packet Radio (NPR-70) is an open-source digital data protocol developed by Loïc Fejoz F4HDK to provide high-speed, IP-based networking over the 70 cm amateur band (420–450 MHz).  Unlike traditional AX.25 packet systems, NPR-70 uses modern digital modulation and framing techniques to carry standard Ethernet or IP data directly between radios, enabling data rates typically between 100 kbps and 500 kbps, depending on bandwidth, coding rate, and signal conditions.  The system is designed for point-to-point or point-to-multipoint links, supporting routing and bridging to conventional IP networks, making it ideal for Winlink gateways, remote site control, or as a UHF overlay for AREDN networks.

Built on inexpensive embedded hardware, NPR-70 offers a low-cost, open alternative to commercial microwave data radios.  However, under FCC Part 97 rules in the United States, its capabilities are significantly constrained: encryption is prohibited, third-party commercial Internet traffic cannot be carried, and occupied bandwidth must not exceed 100 kHz in the 70 cm band, which limits throughput to around 56 kbps.  These restrictions make NPR-70 a powerful but legally limited tool.

There has been some experimentation with NPR-70 in the area, but no infrastructure or permanent installations are known to exist.

For more information:

►  Hackaday - NPR New Packet Radio

AREDN

Amateur Radio Emergency Data Network (AREDN) is an open-source project that repurposes commercial Wi-Fi hardware to create high-speed, long-range, IP-based mesh networks for amateur radio operators.  Operating on amateur microwave bands (typically 2.4 GHz or 5.8 GHz) under Part 97 rules, AREDN firmware replaces standard router software with a custom Linux-based system optimized for ad hoc mesh networking.

Each node automatically discovers and links with nearby nodes, forming a self-healing network capable of carrying standard IP traffic—such as voice over IP, video, email, and web applications—without reliance on the Internet.  Originally developed from the Broadband-Hamnet project, AREDN is now widely used by emergency communications groups, ARES/RACES teams, and technical experimenters to build resilient, rapidly deployable data networks for public service and disaster response.

Locally, RATS operates a 3-sector 5.8 GHz AREDN node from our repeater site in southwest Richmond, at a height of around 200 feet.

For more information:

►  RATS:  AREDN Introduction
►  RATS:  Join the Mesh
►  AREDN Mesh Project

Meshtastic

Meshtastic is an open-source digital mesh networking platform that can operate within the amateur radio service under FCC Part 97 when configured on authorized frequencies and by licensed operators.  Using LoRa (Long Range) modulation on the 420–450 MHz and 902–928 MHz amateur bands, it allows licensed hams to experiment with low-power, long-distance data communication using inexpensive, open-hardware nodes.  Each node can relay encrypted or unencrypted text messages, GPS position reports, and telemetry, automatically forming a self-healing mesh that extends coverage without centralized infrastructure.

In the amateur context, Meshtastic serves as a powerful digital experimentation and emergency communications tool.  Operators can integrate Meshtastic with gateways, sensors, or cross-band links to other networks, creating resilient, IP-less data systems ideal for field operations, search-and-rescue, and EMCOMM use where traditional networks are unavailable.

For more information:

►  Catastrophic Amateur Tactical Squad (KC4TS)
►  Meshtastic
►  Meshtastic:  Amateur Radio FAQ

DMR IP Data

In addition to its voice and messaging capabilities, Digital Mobile Radio (DMR) also supports IP data transport.  It is best suited for UDP applications with small packet sizes and infrequent transmissions.  Connectivity requires a Motorola radio, USB cable, and special codeplug configuration.  It is easy to send and receive ETSI standard SMS and Motorola TMS messages over the data interface to individual radios or to talkgroups.

Several members of RATS have been experimenting with DMR IP data applications over the past few years.  We have several good resources here on our site.

For more information:

►  RATS:  DMR IP Data & Messaging
►  RATS:  DMR IP Data & Messaging - Station Identification
►  Rocky Mountain Ham Radio:  IP Data over DMR (YouTube)
►  Rocky Mountain Ham Radio:  IP Data over DMR (PDF)