Category:SWIFT-3k: Difference between revisions
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[[File:Obraz.png|300px|thumb|right|Leader tone -> Traffic burst]] | [[File:Obraz.png|300px|thumb|right|Leader tone -> Traffic burst]] | ||
[[File:Obraz_(1).png|300px|thumb|right|Deeper look into the burst]] | [[File:Obraz_(1).png|300px|thumb|right|Deeper look into the burst]] | ||
'''SWIFT-3k''' | '''SWIFT-3k''' (Also known as OFDM) is a 49-tone OFDM PSK Russian military multi-channel modem. It features scrambled voice/ data-communication at a maximum data rate of 7333 bps. Each subcarrier can transmit up to 44.1 Bd. | ||
This waveform is transmitted by the SWIFT-3k, SWIFT-3k-2, SWIFT-3k-3 and the newer SWIFT-3k-4 modem versions in use by the multiple operators but Guest Radio operator mostly. These modems were designed to have many different devices plugged into them to form the modem’s input – most often teleprinters unique to the different military services and civilian agencies that use them, and also, vocoders and speech encipherment systems, but all are transmitted in the same fashion. | This waveform is transmitted by the SWIFT-3k, SWIFT-3k-2, SWIFT-3k-3 and the newer SWIFT-3k-4 modem versions in use by the multiple operators but Guest Radio operator mostly. These modems were designed to have many different devices plugged into them to form the modem’s input – most often teleprinters unique to the different military services and civilian agencies that use them, and also, vocoders and speech encipherment systems, but all are transmitted in the same fashion. | ||
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|≈ 2.3 kHz | |≈ 2.3 kHz | ||
|−26 dB points at roughly 350 and 2650 Hz. | |−26 dB points at roughly 350 and 2650 Hz. | ||
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|Creator | |||
|guest10074 | |||
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│ 1500 Hz, .6s │30│ 300→ │1│ 1 │ 8 sym │ N symbols │ | │ 1500 Hz, .6s │30│ 300→ │1│ 1 │ 8 sym │ N symbols │ | ||
│ │ms│ 2700Hz │0│ sym │ DBPSK ×5 │ data mode │ | │ │ms│ 2700Hz │0│ sym │ DBPSK ×5 │ data mode │ | ||
│ │ │ 100 ms │ms│ │ │ │ <br /> | │ │ │ 100 ms │ms│ │ │ │ <br />└──────────────┴──┴────────┴─┴─────┴──────────┴──────────────┘ | ||
Logs: | Logs: | ||
none yet | none yet | ||
Revision as of 10:59, 25 September 2026
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SWIFT-3k (Also known as OFDM) is a 49-tone OFDM PSK Russian military multi-channel modem. It features scrambled voice/ data-communication at a maximum data rate of 7333 bps. Each subcarrier can transmit up to 44.1 Bd.
This waveform is transmitted by the SWIFT-3k, SWIFT-3k-2, SWIFT-3k-3 and the newer SWIFT-3k-4 modem versions in use by the multiple operators but Guest Radio operator mostly. These modems were designed to have many different devices plugged into them to form the modem’s input – most often teleprinters unique to the different military services and civilian agencies that use them, and also, vocoders and speech encipherment systems, but all are transmitted in the same fashion.
A characteristic trait of this signal is the unmodulated leader tone at 1500 Hz (But some people use different ones).
Air interface
| Parameter | Value | Why |
|---|---|---|
| Sample rate | 48 000 Hz | Native rate of nearly every sound device. |
| FFT size / spacing | 1024 → 46.875 Hz | Symbol long enough for HF Doppler, short enough to track drift. |
| Guard interval | 64 / 128 / 256 samples | Fast / Standard / Robust — trades throughput for tolerance of path delay spread and timing error. |
| Symbol rate | 44.1 / 41.7 / 37.5 baud | Not signalled — the receiver identifies it from the reference symbol's own guard interval before reading anything else. |
| Carriers | 49 (375–2625 Hz) | Fits a 300–2700 Hz SSB filter with room at both edges. |
| Pilots | 5 at −24, −12, 0, +12, +24 | Carry a known zero phase step; drive the phase loop. |
| Data carriers | 44 | Everything else. |
| Modulation | DBPSK / DQPSK / D8PSK / D16PSK | Differential in time, so no channel equaliser is needed. |
| FEC | K=7 (171/133), rate ½ / ⅔ / ¾ | Soft-decision Viterbi; ⅔ and ¾ puncture the same mother code, not separate encoders. |
| Interleaver | Coprime stride, per block | Spreads a 2 kB block over up to 9 s of air time. |
| Occupied bandwidth | ≈ 2.3 kHz | −26 dB points at roughly 350 and 2650 Hz. |
| Creator | guest10074 |
Throughput
| Mode | Gross | Net payload | Reliable from |
|---|---|---|---|
| DBPSK + FEC 1/2 | 1 833 bit/s | 890 bit/s | +4 dB |
| DBPSK + FEC 2/3 | 1 833 bit/s | 1 176 bit/s | +4 dB |
| DBPSK + FEC 3/4 | 1 833 bit/s | 1 317 bit/s | +7 dB |
| DQPSK + FEC 1/2 | 3 667 bit/s | 1 733 bit/s | +4 dB |
| DQPSK + FEC 2/3 | 3 667 bit/s | 2 270 bit/s | +7 dB |
| DQPSK + FEC 3/4 | 3 667 bit/s | 2 534 bit/s | +7 dB |
| D8PSK + FEC 1/2 | 5 500 bit/s | 2 534 bit/s | +9 dB |
| D8PSK + FEC 2/3 | 5 500 bit/s | 3 290 bit/s | +10 dB |
| D8PSK + FEC 3/4 | 5 500 bit/s | 3 660 bit/s | +10 dB |
| D16PSK + FEC 1/2 | 7 333 bit/s | 3 290 bit/s | +17 dB |
| D16PSK + FEC 3/4 | 7 333 bit/s | 4 707 bit/s | +17 dB |
| DQPSK raw | 3 667 bit/s | 3 290 bit/s | +14 dB |
| D8PSK raw | 5 500 bit/s | 4 707 bit/s | +26 dB |
Burst structure
┌──────────────┬──┬────────┬─┬─────┬──────────┬──────────────┐ │ leader tone │ │ chirp │ │ ref │ header │ payload │ │ 1500 Hz, .6s │30│ 300→ │1│ 1 │ 8 sym │ N symbols │ │ │ms│ 2700Hz │0│ sym │ DBPSK ×5 │ data mode │ │ │ │ 100 ms │ms│ │ │ │
└──────────────┴──┴────────┴─┴─────┴──────────┴──────────────┘
Logs: none yet
How to download and use
Ask guest10074 (@guest10074.lua) on Discord. The modem is fully built in HTML so it can be used as a standalone file.
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