Category:SWIFT-3k
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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 and the newer SWIFT-3k 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[edit | edit source]
| 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 / D16APSK | All differential — D16APSK carries amplitude too, the rest phase only. |
| 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[edit | edit source]
| 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 |
| D16APSK + FEC 1/2 | 7 333 bit/s | 3 290 bit/s | +18 dB |
| D16APSK + FEC 3/4 | 7 333 bit/s | 4 707 bit/s | +18 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[edit | edit source]
┌──────────────┬──┬────────┬───┬─────┬──────────┬────────────────┐ │ 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[edit | edit source]
Download here. The modem is fully built in HTML so it can be used as a standalone file.
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