Repeaters
A repeater listens on one frequency and simultaneously retransmits on another from a high elevation, turning a 5 W handheld in a valley into a wide-area station. On VHF and UHF they provide reliable regional coverage; on 10 meters, ionospheric propagation can turn a single repeater into an international DX portal.
Offsets come from the band plan
Part 97 authorizes repeaters on 10 m and above (§ 97.205(b)). Specific channel pairs and offset directions follow regional coordination.
| Band | Repeater outputs | Input / offset | Note |
|---|---|---|---|
| 10 m | 29.620–29.680 MHz | -100 kHz (inputs 29.520–29.580 MHz) | General & Extra only; 29.600 MHz national simplex. Worldwide propagation during F2 / sporadic-E openings. |
| 6 m | 51.62–51.98, 52.5–52.98, 53.5–53.98 MHz | Inputs 500 kHz below (-500 kHz split; 1 MHz on some legacy pairs) | The "Magic Band": local FM coverage plus dramatic sporadic-E openings across North America. |
| 2 m | 145.20–145.50, 146.61–146.97, 147.00–147.39 MHz | 600 kHz: below (-600 kHz) for 145.2–146.97, above (+600 kHz) for 147.00–147.39 | The primary amateur FM & digital voice workhorse; extensive emergency and ARES/RACES coverage. |
| 1.25 m | 223.85–224.98 MHz | Inputs 1.6 MHz below (-1.6 MHz split: 222.25–223.38) | Quiet, intermod-free U.S./ITU Region 2 allocation; widely used for regional linking backhauls. |
| 70 cm | 442.00–445.00 and 447.00–450.00 MHz | 5 MHz split: typically +5 MHz in western states, -5 MHz in eastern coordinators | Dense commercial-grade coverage, DMR/D-STAR/Fusion digital voice, and cross-band satellite work. |
| 33 cm | 927.00–928.00 MHz | -12 MHz or -25 MHz split (inputs 902–903 MHz) | Specialist UHF band popular for converted commercial Motorola/Kenwood hardware. |
| 23 cm | 1270.00–1296.00 MHz | -12 MHz or -20 MHz split | Microwave repeaters, high-speed digital multimedia, and amateur television (ATV). |
Source: ARRL band plan. Always confirm a machine's input tone, offset, and access mode from local coordinators or repeater directories.
10 Meter FM Repeaters: The Worldwide HF Exception
Operating on the boundary between VHF line-of-sight and HF skywave propagation.
How 10 m Repeaters Work
Unlike VHF/UHF repeaters whose coverage is constrained to a 30-to-60 mile radio horizon, 10 meter FM repeaters (operating between 29.500 and 29.700 MHz) interact directly with the ionosphere. During solar cycle peaks (F2 layer reflection) or summer Sporadic-E openings, a 10 m repeater can open worldwide. A mobile station with a 50 W transceiver and an omnidirectional vertical whip can work stations thousands of miles away through a mountaintop 10 m machine.
Standard channels run at 20 kHz channel steps with a -100 kHz offset:
- Repeater Inputs: 29.520, 29.540, 29.560, and 29.580 MHz.
- National Simplex Calling: 29.600 MHz FM (keep clear of repeater traffic).
- Repeater Outputs: 29.620, 29.640, 29.660, and 29.680 MHz.
- Mandatory Continuous Tone (CTCSS): When 10 m propagation opens, repeaters on the same channel across the country hear each other. Without strict CTCSS tone guarding on both input and output, machines can lock each other into an endless cross-keying feedback loop ("kerchunk ping-pong").
- Cross-Band Linking: Many 10 m repeaters link their receiver audio to an associated 2 m or 70 cm repeater system, allowing local VHF handheld operators to monitor 10 m HF band openings without needing large HF mobile antennas.
- Statutory Power Ceilings: Repeaters on 10 m operated by General and Extra class licensees are authorized for up to 1,500 W PEP (§ 97.313(b)), though most commercial sites run 100 W to 250 W continuous duty.
Digital Voice Repeaters (DMR, Fusion, D-STAR)
Modern amateur repeaters combine traditional analog FM with digital voice protocols and internet routing.
| Protocol | Access method | Vocoder / codec | Networks & linking | Strengths |
|---|---|---|---|---|
| DMR (Digital Mobile Radio) | 2-Slot TDMA (2 simultaneous QSOs per 12.5 kHz channel); Color Codes (0–15); Talkgroups (TG) | AMBE+2 (vocoder chip required) | BrandMeister, TGIF Network, DMR-MARC | Offers two independent voice channels on a single repeater frequency through time-division multiplexing. Global talkgroups enable crystal-clear world roaming with low battery consumption. |
| Yaesu System Fusion (C4FM) | FDMA (12.5 kHz); Automatic Mode Select (AMS); DG-ID (Digital Group ID 0–99) | AMBE+2 | WIRES-X, YSF Reflectors, FCS Rooms | Excels in seamless operation: AMS automatically detects incoming analog FM or digital C4FM and transmits back in the matching format, eliminating operator mode errors. |
| D-STAR | FDMA (6.25 kHz / 12.5 kHz); Callsign-routed (MyCall, UrCall, RPT1, RPT2) | AMBE / AMBE+2 | D-STAR Gateway (trust servers), REF, XRF, DCS reflectors | The original amateur digital voice system. Uses callsigns directly as network addresses rather than integer IDs, allowing automated point-to-point callsign routing and simultaneous GPS/DPRS data. |
| P25 (Project 25) | FDMA (12.5 kHz); NAC (Network Access Code) squelch; Talkgroups | IMBE / AMBE+2 | P25NX, BrandMeister bridges | The mission-critical public safety standard. Known for robust error correction in weak-signal fringe areas and excellent interoperability using surplus commercial public-safety gear. |
| M17 Protocol | 4FSK FDMA (9600 bps stream on 12.5 kHz channel) | Codec 2 (Patent-free, open source) | M17 Reflectors (mrefd) | A completely open, hardware-agnostic digital voice and data protocol free from proprietary vocoder royalties. Runs on open firmware (OpenRTX) and custom SDR repeaters. |
Access tones & squelch
Most analog FM repeaters require a sub-audible CTCSS (PL) tone or digital DCS code on your transmit carrier to open the repeater's squelch.
Always set your radio's transmit tone (Tone / T-CTC) to the published frequency. Setting a receive tone (Tone Squelch / T-SQL) is optional: it keeps your receiver quiet when other signals or noise hit the frequency, but prevents you from hearing weaker stations or the repeater tail if tone encode dropouts occur.
On digital repeaters, access is governed by digital identifiers: Color Codes and Talkgroups on DMR, DG-ID numbers on Fusion, or RPT1/RPT2 callsign routing on D-STAR.
VoIP Linking & Wide-Area Networks
Connecting standalone mountain repeaters into regional nets and global reflectors via the internet.
Architecture: Asterisk Open Source PBX / SIP
Control: DTMF node numbers (e.g. *3 + NodeID)
High-fidelity VoIP linking engine run on Linux/Raspberry Pi. Delivers uncompressed telephone-grade audio and powerful macro automation for linking hundreds of repeaters into statewide emergency nets.
Architecture: TCP/IP client-server network
Control: DTMF 4-to-6 digit node numbers
World's most accessible linking network, allowing licensed hams to key into distant repeaters from laptops, iPhone/Android apps, or RF simplex links using callsign-verified accounts.
Architecture: Dedicated embedded Linux nodes / PTT boards
Control: DTMF 4-digit reflector/node codes
Pioneered secure radio-to-radio internet linking. Uses dedicated hardware interfaces to prevent internet-originated PC audio from keying repeaters directly.
Architecture: Yaesu proprietary VoIP routing
Control: One-touch radio buttons / DTMF
Bridges Yaesu Fusion repeaters and personal nodes into interconnected "Rooms" worldwide, supporting voice, text messages, and image transfer.
Typical site components
Common functions in a duplex repeater installation; the exact hardware follows the site design and duty cycle.
- Transmit/Receive Isolation & Duplexers: Because a repeater transmits and receives simultaneously on the same antenna, the powerful transmitter output will overload (desense) the sensitive receiver without severe isolation (≥ 80 to 100 dB). Tuned resonant cavity filters (band-pass and notch duplexers) reject the transmitter frequency from entering the receiver front end.
- Repeater Controller: The brain of the site. Controls PTT keying logic, courtesy beeps, automatic CW or voice call sign identification (§ 97.119), timeout timers (typically 3 minutes), CTCSS tone validation, and auxiliary emergency shutdown links.
- Antenna & Hardline: High-gain commercial fiberglass collinears fed with low-loss solid-shield coaxial cable (such as 1/2" or 7/8" Heliax) to prevent intermodulation distortion and minimize feedline loss.
- Power & Thermal Duty Cycle: Unlike mobile or handheld radios designed for 10% transmit duty cycles, repeater transmitters require continuous 100% duty cycle commercial power supplies and heavy heatsinks or forced-air cooling fans.
- Site Grounding & Arrestors: Single-point ground panels, copper bonding straps, and gas-discharge coaxial lightning surge arrestors bonded to the tower and building earth ground system.
Etiquette, courtesy beeps, pausing between transmissions, and tone settings are on the operating tips page.
Band edges, mode segments, and national calling frequencies are on the amateur bands chart.