What is FSKID?
MMSSTV includes an FSK identification system that can send station information in addition to the SSTV picture. The original documentation calls this function FSKID.
MMSSTV sends FSKID using 45.45 baud FSK. Each symbol consists of six data bits, identified as B5 through B0.
Tone sequence
| Signal | Frequency | Duration |
|---|---|---|
| Initial tone | 1500 Hz | 300 ms |
| Second tone | 2100 Hz | 100 ms |
| Start bit | 1900 Hz | 22 ms |
| Data bit 1 | 1900 Hz | 22 ms |
| Data bit 0 | 2100 Hz | 22 ms |
Callsign encoding
Callsign information is transmitted as a sequence containing the callsign characters together with a checksum.
$2A C1 C2 ... CN $01 XSUM
The checksum is calculated using XOR across the callsign characters. MMSSTV uses modified ASCII values for the transmitted character data.
Contest numbers
MMSSTV can append contest information after the callsign. The original specification describes both compact numeric contest numbers and arbitrary text strings.
Numeric contest numbers of three or four digits, below 4096, are sent using upper and lower six-bit values. Longer or arbitrary contest strings use the same six-bit character concept as callsign data.
Open compatibility
Makoto Mori explicitly stated that programmers may freely implement an MMSSTV-compatible FSKID system in their own programs without requesting permission.