Technical characteristics of Voice and Fax HF transmissions
Voice Transmissions:
- Modulation: SSB (J3E)
- Emission code: 2K80J3E
- Signal: Analogue
- SSB Receiver tuning frequency: As per the 'published' frequencies
Facsimile Transmissions:
- Modulation: FSK (F3C)
- Emission code: 3K00F3C
- FSK Carrier: 1900 Hz
- Shift: White +400 Hz, Black -400 Hz
- Scan line frequency: 2 lines per second (120 lines per minute)
- Scan line stability: Within 5 parts in 1,000,000
- Index of co-operation: 576
- Scanning line density: 3.8 lines per millimetre (96 lines per inch)
- Picture format: Comprises start, phasing, picture and stop sequence as detailed below
- Start signal: Carrier modulated for 5 seconds by alternate Black and White at a rate of 300 Hz
- Phasing signal: 60 scan lines, each scan line comprising White level for 25 milliseconds followed Black level for 475 milliseconds
- Picture signal: Line to start with 25 milliseconds White level, followed by one line of picture content uniformly occupying the remaining 475 milliseconds. This format to continue until entire picture content has been transmitted
- Stop signal: Carrier modulated for 5 seconds by alternate Black and White at a rate of 450 Hz, followed by 10 seconds of Black level
- SSB Receiver tuning frequency: (for a standard WMO facsimile decoder) 1.9 kHz below the published transmit frequencies
- Tuning Tone: Most charts are preceded by 60 seconds of 'tuning tone' (white signal) to allow receivers to automatically tune and capture the chart.
The 'tuning tone' precedes the scheduled transmission time of a chart.
Some charts could not be preceded by 'tuning tone' as there is insufficient idle period preceding. To automatically capture these charts, set your receiver to wake up 2-3 minutes earlier and tune-in on the tail-end to the previous transmission.
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