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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''' (Also known as OFDM, Guest's modem) 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.  
'''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-3 modems 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 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).
A characteristic trait of this signal is the unmodulated leader tone at 1500 Hz (But some people use different ones).
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|-
|-
|Modulation
|Modulation
|DBPSK / DQPSK / D8PSK / D16PSK
|DBPSK / DQPSK / D8PSK / D16PSK / D16APSK
|Differential in time, so no channel equaliser is needed.
|All differential — D16APSK carries amplitude too, the rest phase only.
|-
|-
|FEC
|FEC
|Rate ½, K=7 (171/133)
|K=7 (171/133), rate ½ / ⅔ / ¾
|Soft-decision Viterbi, ~5 dB of coding gain.
|Soft-decision Viterbi; ⅔ and ¾ puncture the same mother code, not separate encoders.
|-
|-
|Interleaver
|Interleaver
Line 56: Line 56:
|≈ 2.3 kHz
|≈ 2.3 kHz
|−26 dB points at roughly 350 and 2650 Hz.
|−26 dB points at roughly 350 and 2650 Hz.
|-
|Creator
|guest10074
|
|}
|}


Line 65: Line 69:
!Reliable from
!Reliable from
|-
|-
|DBPSK + FEC
|DBPSK + FEC 1/2
|1 833 bit/s
|890 bit/s
| +4 dB
|-
|DBPSK + FEC 2/3
|1 833 bit/s
|1 833 bit/s
|821 bit/s
|1 176 bit/s
| +4 dB
| +4 dB
|-
|-
|DQPSK + FEC
|DBPSK + FEC 3/4
|1 833 bit/s
|1 317 bit/s
| +7 dB
|-
|DQPSK + FEC 1/2
|3 667 bit/s
|3 667 bit/s
|1 700 bit/s
|1 733 bit/s
| +4 dB
| +4 dB
|-
|-
|D8PSK + FEC
|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
|5 500 bit/s
|2 571 bit/s
|2 534 bit/s
| +9 dB
| +9 dB
|-
|-
|D16PSK + FEC
|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
|7 333 bit/s
|3 290 bit/s
|3 290 bit/s
| +17 dB
| +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
|DQPSK raw
|3 667 bit/s
|3 667 bit/s
|3 182 bit/s
|3 290 bit/s
| +14 dB
| +14 dB
|-
|-
|D8PSK raw
|D8PSK raw
|5 500 bit/s
|5 500 bit/s
|4 841 bit/s
|4 707 bit/s
| +26 dB
| +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 │    │          │                │ <br />└──────────────┴──┴────────┴───┴─────┴──────────┴────────────────┘


Logs:
Logs:
none yet
none yet


== How to download and use ==
[https://qu.ax/Ypnkm Download here.] The modem is fully built in HTML so it can be used as a standalone file.
----
----
[[Category:Modems]]
[[Category:Modems]]

Latest revision as of 19:37, 28 September 2026

Leader tone -> Traffic burst
Deeper look into the burst

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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