Mystery Signals Of The Short Wave

This station was originally reported in January 1998 by ENIGMA on 5305 kHz, transmitting a carrier for exactly 20 minutes every hour, on the hour, 24 hours a day.

Originally named "The Blank Carrier", it is in fact a modulated signal which sounds like a low burbling hum.  Examination of the signal shows that it consists of two distinct tones, peaking 250 Hz apart.

This would indicate it is a simple two-frequency FSK, (Frequency Shift Keying),  system.

This type of FSK transmission, called RTTY (RadioTeleTYpe), are used by both amateur and commercial operators, and transmit two closely spaced signals,(i.e. frequency-shifted,) less than 1 kHz apart, to provide the Mark - Space signals for sending data over the radio. In the receiver, an injected beat frequency converts these two signals into audio toneswhich, using the Baudot code are then displayed as ASCII symbols. Various speeds and frequency-shifts are used.

The "Twenty Minute Idler" uses an unusual frequency-shift of 250 Hz.

  "The Twenty Minute Idler"  (47 kb)

Rimitas Pleikys in Lithuania noted on 24 March 1999, that there were three closely spaced signals operating on 5305.5,   5307.5   &  5308 kHz. Each was operating independently, transmitting from 2000 UTC for 20 minutes,  40 minutes &  60 minutes respectively.   The signal strength of each signal also varied, the strongest being 5305.5 kHz giving a hefty S5 in Lithuania.  Here in Southern England, only 5305 kHz had been monitored by me, and this was giving only an S3 reading here.

On 7 April 1999 Rimitas further reported signals on 4049 kHz,   4301 kHz,   4705 kHz,   & 6801 kHz   as well as 5305 kHz.

In England, in 1999, 4049 kHz, 4301 kHz, 5305 kHz and 6801 kHz could be clearly heard from early evening, transmitting for exactly twenty minutes.

When I updated this page in 2008, I was surprised to note that very little had changed except that the 4049 kHz frequency has possibly been dropped - it was not heard by me despite monitoring the channel on various days and times.

The other three frequencies heard in the UK during 1999, 4301 kHz, 5305 kHz and 6801 kHz, were still clearly transmitting the idler tone for 20 minutes every hour, and probably due to conditions prevailing at the time were clearly audible in South East England during most of the 24 hour period.

So what purpose have these stations, are they back-up facilities in case of satellite failure? Are these utility signals or do they have a military purpose?

Sincere thanks to Rimitas Pleikys from Lithuania for his work on this signal, and for allowing it to be published here.

All comments, suggestions welcome!