C4FM

Yaesu’s digital voice and data modulation with 4-level frequency shift keying — easy to use and connected worldwide via Wires-X.

C4FM (Continuous 4-level Frequency Modulation) is a digital modulation technique for the transmission of voice and data. Frequency modulation utilises four frequencies. C4FM was developed by Yaesu as a competitor to and complement for DMR (Hytera, amongst others) and D-STAR (Icom). As well as voice, C4FM also enables the transmission of images and text messages — even handheld radios such as the FT-5D or mobile units such as the FTM-300 and FTM-400 can establish global connections via the Wires-X network.

System Fusion, C4FM and Wires-X

Three terms are often confused: C4FM is the modulation scheme (four-level frequency shift keying). System Fusion is Yaesu’s implementation of this technology in radio transceivers and repeaters — the digital voice standard that a Yaesu device uses for ‘over-the-air’ communication. Finally, Wires-X is Yaesu’s internet networking system: it connects Fusion repeaters and PC nodes worldwide to form ‘rooms’ — comparable to the reflectors in D-STAR or the talkgroups in DMR.

Wires-X requires Yaesu’s own hardware. YSF reflectors and the more powerful YCS (Yaesu Connect System) have established themselves as open alternatives, networking Fusion repeaters without a Wires-X PC; Yaesu’s DR-2X repeaters can also be interconnected directly via IMRS (Internet-linked Multi-site Repeater System). Using a personal hotspot with the Pi-Star software, you can access the YSF network even without a local repeater, and bridges can be used to link C4FM channels to the DMR network (Brandmeister) — several Swiss channels make use of this (see below).

How it works and how to use it

C4FM is the digital standard that Yaesu incorporates into its radio transceivers. For cross-regional or worldwide QSOs, a Wires-X box can be connected to the repeater — the end user does not need to programme anything additional on the radio transceiver.

Yaesu’s System Fusion is incredibly simple. It requires no programming — you simply need to enter your call sign (e.g. HB9AYZ) and you can start transmitting via the Yaesu repeater straight away. Important: enter only the call sign; do not include a first name or any suffixes. The repeater automatically detects whether the signal is an analogue FM signal or a digital C4FM signal and switches accordingly. The radio transceiver can also be set to auto-detection — on the Yaesu FT1DE, for example, a bar next to the mode indicates that this function is active. Drawback: occasional audio dropouts may occur during FM reception.

Yaesu System Fusion supports four C4FM modes; in voice mode, the two most important are DN and VW:

  • DN (Digital Narrow, ‘V/D Mode’) — the standard mode: the channel is split — one half carries the digital voice, the other error correction and additional data such as call signs and GPS position. This results in robust voice transmission along with position display (coordinates and distance to the other station).
  • VW (Voice Wide, ‘Voice FR’) — the full bandwidth is available for voice: best sound quality, but without the parallel data channel (no GPS).

In addition, there is the DW (Data FR) mode for the rapid transmission of images and text, as well as the analogue FM mode; in Auto mode, the device selects the appropriate mode automatically.

With Yaesu System Fusion, it is strongly recommended that a tone squelch (e.g. 88.5 Hz) be activated on both the transmit and receive sides when operating in analogue FM mode — otherwise, FM stations on the air will pick up digital noise with every digital voice transmission.

C4FM in Switzerland

In Switzerland, the Fusion repeaters are networked in several ways — not just via Yaesu’s Wires-X. In addition to the Wires-X rooms, the open YSF/YCS system and Yaesu’s IMRS are used, along with bridges to the DMR network. Specific examples:

  • SWISS-CONNECT (HB-CONNECT Association) — the large, supra-regional Swiss network, offering extensive coverage thanks to numerous repeaters at strategic locations. Accessible via Wires-X (ROOM #28878), via the YSF network and via the DMR talk group TG22820; HB-CONNECT also operates a bridge between the YSF and Wires-X networks.
  • HB9T (Thun) — Wires-X ROOM #47052, also connected to the fire chief via the DMR talk group TG22826.
  • Several repeaters (e.g. HB9DR-3 and HB9DR-5) are networked via the YCS/IMRS system, which operates without a Wires-X PC.

Yaesu maintains an up-to-date list of all Wires-X rooms at yaesu.com/wires-x/active_room. HB9SH provides a German-language introduction to C4FM, YSF and Wires-X as a PDF: hb9sh.ch — C4FM, YSF and Wires-X.