WHAT IT IS

CIS-81-81 is the dual-channel FSK telegraph of the T-206 family. Monitor aliases: 81-81, CIS-8181, Moroz (Мороз, “Frost” — old nickname). Hardware card: T206-M 3M1. It is not a new modulation. It is two CIS-40.5 streams on one mark/space pair, bit-interleaved, so the line rate reads ~81 baud (2 × 40.5).

Sigidwiki’s CIS-8181 short card lists Russian Navy and ~600 Hz occupied width — same FSK look as CIS-40.5, twice the bit clock. Same Wesna encryptor lineage as the single-channel page.

WHAT THE WATERFALL LOOKS LIKE

Two rails. Logged shifts include 250 Hz and 500 Hz (WUN-era list also 125 / 200 / 1000 / 1500 Hz by user class). Occupied width on the navy card ~600 Hz. USB. Idle at 81 Bd / 250 Hz shows a 24-bit mark/space block (12 + 12). CIS-40.5 idle on the same shift is 12 bits (6 + 6). Faster tweet than 40.5; still a classic FSK pair, not a 12-tone comb and not BEE’s 36/50 clock.

HOW THE AIR INTERFACE WORKS

Two logical channels A and B, bit-interleaved on one FSK. I-56578 / old handbook split:

— 6-bit format @ 40.5 Bd — single channel (CIS-40.5): idle or traffic
— 12-bit format @ 81 Bd — dual channel: A+B idle; A traffic / B idle; A idle / B traffic; A+B traffic. Bits 2 and 5 inverted in the published 12-bit picture.

On 81 Bd / 250 Hz samples: idle 12 mark + 12 space, then a block scrambled with PRBS x^11 + x^9 + 1 (test or pre-crypto), then idle inverted. Same polynomial on the 500 Hz 81 Bd dumps. Traffic in both channels encrypted. Hoka files the family under 81-81 and 81-29.

BANDS AND WHERE IT IS HEARD

HF USB, 3–30 MHz. Historical WUN user notes (not a current allocation): 125 Hz navy; 500 Hz railway; 200 / 250 / 500 Hz military. Legacy catch. Pair it with the CIS-40.5 page; do not treat 81-81 as navy BEE.

HARDWARE

T206-M 3M1 on the cipher-modem side (Wesna 3M/3M1 vehicle-sized boxes). Radio is the HF set that takes the FSK pair. Decoder: Hoka 300-32 81-81 / 81-29.

NOT THESE

CIS-40.5 — same family, one channel, 40.5 Bd.
CIS-36-50 / BEE / T-600 — navy 36/50 FSK, different box.
CROWD-36 — 36-tone MFSK.
CIS-12 — 12 parallel PSK + 3300 Hz pilot.

CAVEATS

81-81 vs CIS-8181 is spelling. Moroz is a nickname. Dual-channel is TDM/bit-interleave on one pair, not two RF carriers. Shift lists wander.

STATUS

Legacy. Catalogue next to CIS-40.5. Do not expect it beside live CIS-12 every night.

IN ONE SENTENCE

CIS-81-81 / Moroz is the T206-M 3M1 dual-channel FSK telegraph — two 40.5 Bd Wesna streams bit-interleaved at ~81 Bd on one mark/space pair — the two-pipe sibling of CIS-40.5, not navy BEE and not CROWD-36.