VARA HF implementation constants

VARA is an alpha implementation with successful live Winlink mail transfers, including full-speed transfers. That milestone is broader than the retained Winlink examples: the send reaches acknowledged L9, and the receive is speed-limited L4. A separate VarAC recording contains CRC-valid BW500 receive frames at L5, L6 and L7. Bench validation across every codec row remains separate from RF validation of a named session at a named rate.

The illustrated guide explains the waveform families and the high-speed pipeline. This map supplies the exact constants behind that explanation via public source and the detailed protocol chapters. Built-site source links are local and line-numbered. No private installation, extracted table directory or unpublished Git history is needed to follow them.

A shared chain, three waveform families

Every DATA frame is payload, one control byte and a big-endian CRC-16/GENIBUS. Bits are MSB-first, zero-padded to the record's information size, whitened from PN index zero, turbo encoded on the record's stage-2 permutation, punctured to its coded size, then gathered by stage 1. Index modulation selects one lit bin; tone modulation keys differential phase increments; OFDM maps bit groups to full constellation columns and scrambles each cell's phase. MFSK calling/answer bursts use their own callsign-derived tone sequence, with no DATA whitening, interleaving or FEC.

The two turbo constituents have the same eight-state recurrence: a=u XOR r1 XOR r2, p=a XOR r0 XOR r2, next (a,r0,r1). Both start in zero state and terminate with three steps each. The wire tail is [s1,p1,s2,p2] repeated three times. Rate 1/3 retains all three streams; rate 1/2 alternates the constituents' parity. Higher rates group systematic bits with one parity, alternating C1/C2 by group; the exact record size determines any final zero padding. These rules define VARA’s tail placement and parity multiplexing.

High-speed OFDM geometry

At 48 kHz, each symbol is a 1024-point IFFT plus a 128-sample cyclic prefix: 1152 samples, 41⅔ symbols/s, with 46.875 Hz bin spacing. Transmit synthesis uses a 32-sample edge blend. Rows are filled bin-major, skipping references, pilots and generator-defined gap cells. PSK is differential in time; QAM is coherent on pilots, not differential.

Bandwidth	OFDM levels	Active FFT bins	Carriers
500	L7–13	27–37	11
2300	L10–16	8–56	49
2750	L11–17	3–61	59

Each bandwidth follows seven OFDM rows in this order:

Row	Constellation	Nominal code rate	Group size k
1	differential QPSK	1/2	1
2	differential QPSK	2/3	2
3	differential QPSK	4/5	4
4	differential 8PSK	2/3	2
5	differential 8PSK	4/5	4
6	coherent 16QAM	5/6	5
7	coherent 32-cross QAM	4/5	4

PSK has four lead rows, a reference and 148 data rows (153 total). QAM has five lead rows followed by 154 rows per frame; pilots appear at 8*j on even FFT bins and 8*j+1 on odd bins relative to the frame start. The highest row can carry two frames: 313 rows instead of 159. BW2750 L17 carries 3922 net bytes (3919 payload) per frame. The nominal top rate is approximately 8489 bps; this is a speed descriptor, not a promise of delivered application throughput. The complete level tables supply information bits, coded bits, field bytes and timing for every row, not only the top level.

Every table input has a public definition

Implementation input	Public definition and coverage
All bandwidth/level seeds and sizes	tablegen.BW500, tablegen.BW2300, tablegen.BW2750; 17 `(seed,coded,N)` records per bandwidth. BW2750 shares the first nine BW2300 records, then its own chain.
PRNG and permutation rounding	tablegen.step, tablegen.draw, tablegen.permutation; 24-bit VB6 recurrence, exact float32 multiplication/rounding and unique-value rejection. An integer floor shortcut is not equivalent. Stage 2 continues stage 1 state; each record’s remaining draws produce its gap/pilots and close on the next seed.
Whitening and phase scramble	tablegen.whitener uses seed 29318 and the high state bit. tablegen.scramble separately starts seed 29318, generating a 62×409 row-major table of `draw(129)` values; multiply cells by `exp(-j2pi*S/128)`.
Full constellation geometry and labels	tablegen._column / tablegen._cross32 construct complete columns. Raw bit groups index them directly at OFDM levels, without an extra Gray pass. 32-cross is a 6×6 odd-coordinate grid with four corners removed, axis unit `0.3/sqrt(2)`. The historic 64-entry interleaved LUT is a truncated prefix, not all 32 labels.
FEC, dual tails and puncturing	turbo._step, turbo.encode, turbo.encode_r13 and turbo._groups / turbo.encode_punctured; full trellis, tail order, group law, pad and soft-decode conventions.
CRC	crc; GENIBUS polynomial 0x1021, init/xorout 0xFFFF, no reflection, big-endian trailer.
OFDM rows, pilots, fill and receiver	varaofdm.OfdmRecord / varaofdm.ROWS supply all 21 rows’ geometry, full labels, channel/turbo permutations, pilot/gap layout and scramble. tablegen.gap_cells specifies exact missing/repeated cells.
OFDM transmitter and edge blend	varaofdm_tx assembles frames, maps cells, carries differential state and renders CP/blend. Its output RMS is a local convention; its header/tail bytes are explicit.
Tone rows and shaping	varatone.ROWS and varatone_tx cover per-band geometry, labels and reference state; tablegen.grid_row / tablegen.tone_pilots define reference grids and pilots. Exact pulse coefficients: tone_pulse and bw500_pulse.
Index rows, measured allocation constants	varahf2300 / varahf2300_tx and varahf500 / varahf500_tx define emission columns, strides, reference rows and coding. tablegen contains the complete base-bin literals and constructors; bw2750_allocations gives the widest base allocations.
MFSK calling, native answers and tokens	vara_frames contains alphabets, preambles, callsign hash/seed derivation, packed callsigns, answer/control tails and session tokens. vara_mfsk and vara_control specify tone placement, pulse overlap and token waveforms.
Session lead state and draw cost	vara_frames.lead_state seeds the caller/responder stream. varaofdm_tx.cells advances it by `lead*carriers` per frame, in bin-major order; a two-frame over consumes two lead blocks and transmits the second. varatone_tx and varahf2300_tx supply tone/index lead laws.
Frame sizing and ARQ use of levels	phy supplies all native frame capacities, host/internal level mapping, caller-ID framing, control byte and over scheduling; fsm defines adaptation and timed control policy. These thresholds/budgets are implementation policy, not all proven universal peer behavior.
Source compression	compression has Huffman symbols, escapes, mode bits and file framing. Compression evidence and limits distinguish observed code assignments from unclosed cases.

Precision and evidence

The PRNG inputs and table constructors are sufficient to reproduce active DATA permutations and phase tables without an extracted asset dump. Measured bin and pulse literals remain public code constants, with their provenance explained in the relevant source/chapter. A constructor's inactive compatibility padding is not another active speed mode. Full physical detail is in physical layer, coding, frame formats and speed adaptation. Their detailed bench evidence remains available beside the descriptions. Every row being bench-validated does not establish successful RF behavior at every bandwidth and speed.