On 18th July, members were given a beginner’s introduction to simplex operation using Yaesu’s C4FM (Fusion) digital mode.
Yaesu have an introductory video for Fusion, which I found quite helpful when preparing for the talk:
In the UK, 144.6125 is designated as the 2m digital calling channel. Use this for CQ calls using C4FM or other digital modes. Once you’ve established contact, move to a standard FM simplex channel, or use the all modes section of the band. The 144.6375 – 144.7875 range is recommended.
Most Yaesu C4FM radios are capable of five different modes of operation:
| Mode | Appears as | Used for |
| FM | FM | Conventional FM for communication with non-digital users. |
| V/D (Simultaneous Voice and Data) | DN | Error corrected digital voice. This is the “normal” C4FM mode. |
| Voice FR (Full Rate) | VW | Higher bitrate digital voice, allowing for better audio quality when error correction is not required. |
| Data FR (Full Rate) | DW | Sending text or images between C4FM radios. You cannot select this mode manually. Your transmitter will automatically switch to this mode when you use a feature of your radio that requires it. |
| AMS (Automatic Mode Select) | Bar above active mode | The radio will transmit using the displayed mode, but will automatically switch to other modes upon receiving a transmission using one of the other modes. |
The following two videos provide an introduction to analog to digital conversion, and to digital error correction techniques.
A few things to take away from these videos:
- We need to sample our audio at twice the highest audio frequency we wish to transmit.
- We have a fixed amount of bits that we can transmit over a 12.5KHz FM channel.
- Higher audio quality requires more bits to be dedicated to audio data.
- Error correction requires more bits to be dedicated to checks on our audio data, at the expense of audio quality.
- We have to make trade-offs between audio quality and reliability, hence the two different voice modes with different priorities.