Recently, reception reports of respective US Navy stations (Barford, Niscemi, Lualualei, Diego Garcia, among others) appeared on the UDXF mailing list. These stations seem to usage the MS-110A waveform for fleet broadcast, alternatively than the usual STANAG-4481F or STANAG-4285. any of the stations and frequencies reported had already been under reflection by me and my friend Kosmod due to a fewer peculiarities, discussed below.
Non-continuous transmissions
The transmissions we monitored (and are inactive monitoring) are not a continuous stream, as in STANAG- 4481F and STANAG-4285 broadcasts, but consist of bursts of irregular duration separated by short pauses. Figure 1 shows 1 of the receptions of the Niscemi station on 5118.5 kHz USB, recorded on 23 September 2026 at 07:53:58 UTC: the 5 bursts last between about 20 and 43 seconds. Across all our captures, bursts scope from a fewer seconds to a small over a minute.
Curiously, the MS-110A waveform is utilized in the same 600 bps/L mode (600 bps, long interleaver) that is employed in STANAG-4285 broadcasts.
A possible reason for the bursts lies in how the 2 waveforms handle synchronization. With STANAG 4285, the continuous probes sent by the modem keep the receiving side always in sync, and this applies not only to the HF modem but besides to the upper-layer protocol. With MS-110A, a receiver that joins late cannot demodulate until it receives the preamble, so a continuous MS-110A transmission would be lost to any receiver that misses its beginning. Short bursts avoid the problem: each burst opens with its own preamble, so a receiver that joins late can get synchronization at the start of the next burst alternatively of waiting indefinitely. The advanced layer follows the same logic: in the bitstreams we examined, each burst starts with its own alternating run of bits (the "01" run, 1010... in the captured streams) followed by a sync word, so synchronization is restarted at all burst at both levels.
At present it is hard to tell whether these are tests or a lasting change in how the broadcast is run.
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| Figure 1: Spectrogram of a reception of Niscemi on 5118.5 kHz USB, 23 September 2026, 07:53:58 UTC. The dark vertical lines are pauses between bursts; the black band on the right is the end of the file. The burst durations shown (28, 24, 33, 20 and 43 s) are measured values, but only approximate. |
A fixed 32-bit word after the "01" run
The word is identical in all captures and appears only after the "01" run. An alternating run followed by a fixed word is simply a common bit-sync/phasing plus sync-word structure in synchronous data links. As far as we can tell, the word is not part of the MS-110A framing, so it is most likely part of the payload and likely belongs to a link-level protocol or device, specified as a data encryptor. Figures 2 and 3 show the demodulated bitstreams from the 5 stations (yellow = 1, blue = 0, 32 bits per row), showing the alternating run, the row with the sync word and the random-looking data that follows.
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| Figure 2 |
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| Figure 3 |
Structure of the word 0x0A6E14DC
The 32 bits above are not arbitrary. They consist of a single 15-bit pattern, repeated twice, plus the first 2 bits of a 3rd repetition:
000010100110111
000010100110111
00
Read as 2 16-bit halves, the second looks like the first 1 shifted by 1 bit. This is simply a side effect of the period: the real period is 15, not 16.
The polynomial
generator
A pattern like this is produced by a tiny shift registry with only 4 stages. Each fresh bit is the XOR of the erstwhile bit and the bit from 4 steps earlier, which we denote by the polynomial x^4 + x + 1; with the reciprocal convention the same registry is written x^4 + x^3 + 1. This polynomial is of the "maximal-length" kind: the registry passes through all possible non-zero state before repeating, giving the longest cycle possible for 4 stages, 15 bits.
Starting from the registry state 1111 (all ones, a very common choice), the generator produces 111101011001000. The pattern observed on the air is precisely this series with all bit flipped. Inversion does not change the underlying generator, only how the series looks.
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| Figure 4: Left, the 15-bit series produced by the generator from the first state 1111 (the inverse of the 1 observed on the air). Right, schematic of the 4-stage shift register. |
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| Figure 5: Left and center, the 15-bit series as observed on the air, repeated line by line; in a 15-column view it appears as vertical stripes. Right, ranking of candidate generator polynomials x^n + x^k + 1 (pairs n,k) by score, with x^4 + x + 1 on top. |
Common structure of the streams
- all stream starts with an alternating run of precisely 256 bits (128 pairs).
- The 32-bit word appears at position 256 in all 5 streams, bit-for-bit identical.
- The word appears only erstwhile per stream: there is no resynchronization in the mediate of a transmission.
- There are no inverted or bit-reversed versions, so the demodulation polarity is the same in all captures.
What follows the word
I compared 5 bursts, 1 from each station, in pairs (10 pairs), aligned on the end of the word. Over the first 256 bits the percent of differing bits ranges from 46.9% to 56.2%, and over the full common part from 49.8% to 52.0%. Independent streams are expected to give 50%, with a spread of about 3 points over 256 bits, so all values are within average variation. There is no common field right after the word, specified as a shared message indicator, and shifting 1 burst against another by up to 64 bits reveals no shifted copies.
Within each burst, the 0/1 balance is within 1.6 standard deviations of 50%, and neither the runs test nor the autocorrelation shows any periodicity. The lengths of the data after the word are all multiples of 8 bits, and at 600 bit/s the 5 bursts last from about 5 seconds (Barford) to about 75 seconds (Lualualei). Figure 6 shows a set of checks on 1 burst; the another 4 give the same picture.
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| Figure 6: Statistical checks on the data following the sync word of 1 burst (1736 bytes): bit balance, byte histogram, autocorrelation, bit raster and moving proportion of 1s. The another bursts give the same picture. |
