Editing Category:SWIFT-3k

[[File:Obraz.png|300px|thumb|right|Leader tone -> Traffic burst]]
[[File:Obraz_(1).png|300px|thumb|right|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 ==
{| class="wikitable"
!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 ==
{| class="wikitable"
!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 ==
 ┌──────────────┬──┬────────┬───┬─────┬──────────┬────────────────┐
 │ 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:
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.
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[[Category:Modems]]