A few catches from the indoor spectrum grabs

Saturday, June 18, 2016
I am enjoying using my indoor spectrum capture set-up for recording endangered shortwave stations. The set-up relies on my earlier work on mitigating urban radio interference, caused by being in a busy apartment building in London:
I thought I'd share a few of the catches I have made so far. First up, some good music. Here's an atmospheric set from the Voice of Greece on April 21st, 2016 at 2340 UTC:

A beautiful set of qawwalis and ragas from All India Radio Urdu service, recorded on May 23rd, 2016 at 0055 UTC. I especially like the song at 5 minutes 30 seconds into the recording:

I have also been fortunate to catch some more distant transmissions, such as Radio Thailand on 13/06/2016 at 1900 UTC:

A nice bonus that I didn't expect to show up in the spectrum recordings was the Voice of Turkey's English language broadcast on 04/06/2016 at 0300 UTC:

Finally, propagation from Cuba hasn't been great lately and I certainly have much clearer recordings of it from indoors than the one below, but the SDR# software did a fine job of pulling it out from the noise:

Overall, this has been a fun little project and given that I can make these recordings regularly (unlike the trips to my local park), there is a steady stream of gems to be extracted from the radio static and explored.


Morse code transmission over the Voice of Turkey's signal

Thursday, June 16, 2016
I have been regularly recording the small spectrum window containing the endangered stations I mentioned in one of my previous posts. Three days ago I noticed something strange: a morse code transmission superimposed onto the Voice of Turkey's signal on 9460 kHz (video below):

Using SDR# I extracted the coded signal while suppressing the rest of the audio (recording embedded in the player below):

My Morse knowledge is patchy to say the least, so I decoded it using Fldigi. At the start of the recording, the sequence "8T1" is repeated a dozen of times. I Googled around and found another YouTube video of a Morse code transmission from a numbers station, reportedly codenamed M01, which also had multiple repetitions of "8T1".

Numbers stations are still sending messages from many different corners of the world. However, if I indeed captured an M01 transmission in this instance, what makes it unusual is that it was embedded inside a signal from a broadcast station and that it was strong enough to be heard clearly. I'll watch out for further occurrences of M01 on the airwaves.

Update: I received the following pointer from @priyom_org:
While the station supposedly operates daily, it's the first time I heard it over the Voice of Turkey's broadcast at that time of day.