26 December 2015

something broken, tests,... or holidays mistakes

since few days, just 2-3 times a day, I a keep an eye on 11598.0 on USB trying to understand what's going on to a signal that - apparently - should be a normal and peaceful T600 BEE36-50. This FSK synchronous mode, mainly used by the Russian Navy, is very frequent and in many frequencies in HF and is easily recognizable by the messages blocks sent a 50 Baud speed with 200Hz shift, interspersed by reversals.
On 21 december, in the morning, I tuned 11598.0 KHz having seen a signal occupy a rather narrow and odd bandwidth. Measuring the signal, it was a regular T600 transmission but modulated with unusual shift, ~78Hz, and offset although its manipulation speed was the right one (pic.1). 
The signal continued to be transmitted all the day in this strange way, no transmission heard the day after, but again the same behavior on 23 december. On Christmas' Eve everything is back to normal (pic. 2) exhibiting the expected values 50 Baud/200 Hz. A comparison between the two signals is visible in picture 3. Today morning, 26 December, things look even worse: only one keyed tone, the lower, is sent (pic. 4).
The 50Bd/78Hz, although out of rule, could be guessed as a test or as an operational need, but the single - and keyed - tone  suggests a sort of failure of old equipment... or careless mistakes, no one notices? Then, late in the morning again 50Bd/78Hz.
But, it's holiday time after all.

Pic. 1
Pic. 2
Pic. 3
Pic. 4

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