Editing Category:SWIFT-3k (section)

== 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
|
|}