I had an interesting experience this evening listening to the Voice of America’s digital broadcast (I have mentioned this in previous posts) as Hurricane Matthew pounds the eastern seaboard of the Carolinas. The atmospheric noise tonight was almost like the waves of the ocean crashing in along the beach, receding and coming again with a new wave. When I first tuned into the broadcast on 5.745 MHz I could barely hear the opening theme music or the initial voice introduction. I wondered if I would pick up anything at all. Here’s where the beauty of digital modes come in.
I started hearing the first digital transmission softly, yet recognizable. As the moments passed the signal did indeed get a little stronger, but I doubt I would have been able to hear a distinguishable signal had this been a voice transmission without at least earphones, and those might not have been enough to hear someone speak legibly.
I was struck immediately by the usefulness of this digital shortwave broadcast yet again, as it could mean the difference between life and death in an emergency situation. Broadcasting digital modes over a shortwave broadcast station means signals are likely to be heard around the world even when propagation conditions are difficult, a significant advantage over traditional voice broadcasts.
This is not to say I want to see shortwave go digital, but for real emergencies combining voice and data is a really smart move. This is the brainchild of Kim Andrew Elliott, Producer and Presenter VOA Radiogram (voaradiogram.net Twitter: @VOARadiogram) and the program has been a true success, with other stations starting to test digital modes as well.
Here are a few schedules for some of those stations:
The Mighty KBC will transmit to North America Sunday 0000-0200 UTC (Saturday 8-10 pm EDT) on 6145 kHz, via Germany. A minute of MFSK32 will be at about 0130 UTC. Reports to Eric: firstname.lastname@example.org .
DigiDX will transmit MFSK32 and probably other modes:
Sunday 2130-2200 UTC, 15770 kHz, via WRMI Florida
Sunday 2330-2400 UTC, 11580 kHz, via WRMI Florida
Monday 2000-2130 UTC, 6070 kHz, via Channel 292 Germany
IBC (Italian Broadcasting Corporation) has a broadcast to Europe on 6070 kHz, Wednesdays, at the new time of 1800-2100 UTC. The MFSK32 and Olivia 16-500 are still at 2030-2100 UTC. IBC has also added a medium wave transmission Saturday 2000-2030 UTC from Radio Studio X, 1584 kHz, in Terni, Italy, with MFSK32 at 2025-2030. IBC also has MFSK32 transmissions via WRMI in Florida: Friday 0125-0200 UTC on 9955 kHz (Thursday 9:25 pm EDT), part of its 0100-0130 broadcast. And Saturday at 0155-0200 UTC (Friday evening 9:55 pm EDT), on 11580 kHz, part of its 0130-0200 broadcast. See http://ibcradio.webs.com/ for the complete schedule and contact information
I recorded the VOA broadcast and will post some sound clips from it (and hopefully some decodes) when I get some time to play with the audio. I want to see how well fldigi and some other programs decode the original signals, and then do a little post-processing to clean things up a bit and see how the decodes go then.
As an aside, I could have gone directly from radio to computer/software of course, but I have temporarily hooked up my SignaLink USB to my 2-meter/440 rig for some ISS fun. In this case I simply recorded the audio directly from an external speaker, which can work quite well.
I have even done this with my phone in the past and was able to get sufficient quality for decoding. You can simply copy the .wav file to your computer and play it with the digital mode software running. It should “hear” it through the sound card and decode easily.
There is a lot of free software on the Internet for decoding digital signals, with fldigi being the most popular for the VOA transmissions. Why not give it a go and see how things work out?! In the meantime I will get busy decoding and posting my results! Cheers!