Not all unusual radio transmissions are of the voice or CW capacity. This month I want to take a look at an unidentified signal that has been on the air for at least the past eight years.
This is a high-speed data burst signal that I first heard while in England. According to information provided by Day Watson, these signals show up at good levels in the UK and are rumored to be of British military origin. Each burst is 6 seconds long and is sent at 110 baud with a wide 1350 Hz shift. The data is synchronous and is most likely encrypted.
Normally two stations can be heard on the same freq, one signal with a slightly lower pitch. Often one signal is much weaker than the other. It would seem that the two stations are communicating with each other. The transmissions occur at different times past each minute for each frequency used.
Frequency Seconds past top of minute
3295.3 +51
5436 +43 +21
6354 +36 +13
8460 +06 +28
12726.2 +51 +59 +21
16096.2 +43 +13
22139.3 +36 +06
When the transmission times for each minute are compared, no two transmitters are on the air at the same time with the exception of the two transmissions at 6 seconds past each minute. This would suggest that it is possible that there are just a few transmitter sites for this system. Of course, without using any DF or having any other knowledge of this system, it's impossible to tell how many transmitters and transmitter sites are being used. It's obvious that global coverage is desired for this system judging on the wide range of frequencies in use, from 3 to 22 MHZ. As always, there may be more frequencies in use, but the ones listed above are the only known frequencies on which this signal regularly appears.
Which brings us back to the main two questions: Who is operating this system and for what purpose? It is reasonable to suggest that it is being used by the British military as the signal levels are very good in that country. Signal levels are somewhat decent here in North America. I can usually hear it on 5436 and 6354 with fair to good levels, so listeners on the east coast should be able to hear this signal much better. Unfortunately, without knowing much about the system, there's no way to decode the data bursts. We don't know much about these signals, but we do know that it must be a good reliable system as it has been in use for many years.
If anyone would like to receive a .wav file recording of this signal, please email me at the address at the top of the page and I'll be happy to send you a short recording. And of course, if anyone has any information about these signals and would like to share it, I'd be more than happy to include the information here.
That's all for this month. Remember, I would like to include your loggings of numbers stations and other unusual signals in this column every month. If you would like to have your loggings included here, send them to me at either of the addresses at the top of the page. You may remain anonymous if you wish. Also, the Winter SWL Festival in Kulpsville, PA is just around the corner. I am planning on attending and hope to see you there.