Russian Navy single-letter beacons on 7039 kHz: a ladder of Morse letters in the 40 m band

What you hear

With a narrow CW filter around 7039 kHz you hear one letter in Morse, repeated with a short pause: "C, C, C" or "D, D, D" or "P, P, P". Open the filter and the ladder appears. Several letters sound at once, each on a slightly different pitch, because the transmitters sit 100 Hz apart in a fixed order, and on the waterfall they form a neat set of parallel lines. Each letter keeps its own steady pace, some faster, some slower, and none of them ever says anything else. The letters and the places listeners attribute them to are D for Sevastopol, P for Kaliningrad, S for Severomorsk, C for Moscow, A for Astrakhan, F for Vladivostok, K for Petropavlovsk-Kamchatsky and M for Magadan: the bases of the Black Sea, Baltic, Northern and Pacific fleets and the Caspian flotilla, plus the capital.

Who transmits and why

No Russian authority has ever described these beacons in public, so everything known about them comes from listeners: direction finding, decades of logs and the obvious pattern of the sites. The common reading is that they belong to the Russian Navy and serve as channel markers and propagation beacons: a radio operator on a ship or at a shore station tunes to the cluster, sees which letters are readable at this hour on this band, and knows which base can be reached on which frequency without a word being exchanged. The letters were first logged in the 1960s and 1970s, when some of them sat in other ports of the Soviet Union, and the set has changed slowly since: a letter can vanish for months and come back, or change its tempo. Whether the system still has a working role or runs on inertia is not known.

The same ladder is repeated on other bands, with clusters at 3595, 4558, 5154, 7509, 8495, 10872, 13528, 16332 and 20048 kHz, so that at least one is usable at any hour. The 7039 cluster is the best known because it sits inside the 40 m amateur band, in the CW segment, where thousands of radio amateurs hear the letters every evening and have complained about them, to no effect, for as long as they have existed.

When and where to listen

7 MHz is a night and evening band. From a European receiver the letters of the European bases, C, P, D and S, rise with dusk and stay strong until morning; by day they are heard only from receivers within a few hundred kilometres of each transmitter. The Far East letters, F, K and M, are a long shot from Europe and a daily routine from receivers in Japan, Korea and the Russian Far East, where the ladder looks the other way round: strong Pacific letters and faint European ones. A receiver in central Russia hears them all at once.

The catalogue mode is CW with a passband from 300 to 900 Hz, which puts one or two letters in the audio range; widen the filter to hear the whole set, or tune from line to line on the waterfall to pick each letter in turn.

In ShackDeck

Station catalogue → Beacons → Naval single-letter beacons 7039 kHz. The program picks a public receiver that covers 7039 kHz, tunes it in CW with the narrow passband and shows the waterfall, where the lines of the cluster stand side by side. No receiver, antenna or account of your own is needed. The other clusters at 8495, 10872 and 16332 kHz are in the catalogue too, for the evening, the day and the long daytime paths.