Many thanks to SWLing Post contributor, Dan Srebnick, who writes:
While DRM (Digital Radio Mondiale) has long been pronounced DOA (dead on arrival), All India Radio seems to be taking it pretty seriously. Here’s a screenshot of not one, but two simultaneous feeds going out over the same 10 kHz wide 40 meter frequency (7,550 kHz) at 2027 UTC today. The signal on my Perseus was just a tad under S9+5db using my ham band Alpha Delta DX-CC antenna.
So what’s the twist, aside from the 2 feeds on 1 frequency? Even at +5 over S9, the feed was only strong enough to occasionally flutter in with some decoded audio. Mostly, it was silence.
[I had] about a 98% successful decode by 2051 UTC when the signal rose to S9+10 db. I could switch between streams by clicking channel button within Dream!
Dan wrote the message above yesterday, I asked him if he could record AIR today and he kindly sent the following:
AIR DRM recorded today with announcements @ 1930 UTC. Some dropouts as a
great example of the dropout/echo effect heard on DRM when signals are quite
strong enough. This decode was done at S9 signal strength.
Dan actually calls the DRM dropouts, the “Max Headroom Effect.” That is the best description I’ve ever heard, Dan. Thanks for sharing your notes and recording!
Neither does AIR generally use a robust mode with a Main Service Channel (MSC) of 16 QAM for their broadcasts via shortwave. Current power levels for DRM broadcasts using a MSC of 64 QAM aren’t sufficient for reliable decoding on shortwave. Broadcasters’ poor configurations of their digital broadcasts are contributing to the erroneous perception that DRM doesn’t work well on shortwave. DRM is an excellent technology for the shortwave bands, even multiple hops consisting of thousands of miles. However, a MSC of 16 QAM MUST be employed.
These two audio channels have been running on 7550khz for over 6 months, from memory I think one channel is labelled ‘Country Music’. AIR normally smashes into Europe and can be decoded fairly easily. It is a bugbear of mine though that DRM broadcasters use low bitrates on DRM….(AIR audio is ok), fair enough if it is dual channel, but If you use single channel DRM, at least use intelligible audio/bandwidths….VoN take note!
Radio Romania is the broadcaster adopting DRM the best (in Europe at least), although I would like to see them use the DRM features more, like journaline…..at least they have clear and crisp audio!
My philosophy is that Digital audio should be improving the listening experience and not to its detriment.
If broadcasters adopt DRM but use low bitrates and do not use the features available it’s a bit pointless.
I love DRM but get frustrated by the lack of adoption and lack of use of the features available……. Only the BBC and VoR use/have used DRM correctly to date.
This year, DRM will have been “testing” for 20 years. It is never going to fly in a visual world. It’s a classic case of solving a problem that listeners didn’t know they had. India has indeed bought a lot of hardware – I am sure there is a scandal brewing somewhere. It’s going to be useless. RNZ used it for relays to FM stations – that made sense. But not direct to listeners without receivers.
…thanks, Mr. Thomas, for answering my question about the quality of radios from the 1960’s, ’70’s, up to the present day! True, it’s nice to have wooden cases (my father’s old Grundig, Nordmende and Telefunken from the ’60’s and ’70’s), but, they can’t build them anymore with such shellacked wood and mechanical solidity of that time! Maybe because of changing technology and the declining interest of radio and other hobbies (eg. Lionel Trains, etc.), Eton, Tecsun, et. al. have cheaper plastic bodies as radio technology changes quickly, so maybe they just whip out different radios every few months, as well as cell phones!
Another question, and difficult to answer, is why did digital radio (IBOC and DAB in north America) not make any progress? In Australia, west Europe, they broadcast in DRM (digital radio mondiale), but why not here? ….any feedback, please?
Please do not have any illusions about Europe: Shortwave in general and DRM especially are next to dead here. In northern and central Europe mediumwave is dead, too.
The only “new” technology here is DAB/DAB+. Nearly everyone here in Germany listens to FM radio. BTW: The difference between DAB and DAB+ is only the audio codec used. The DAB+ codec compresses better and allows to transmit more programs though a give bit stream.
For long years DAB had a problem with the military that uses the frequenies above: From the beginning the VHF TV channel 12 was only used for small relay transmitters for this reason. Later the relay transmitters moved to UHF freeing their channel for DAB. But these 7 MHz were not enough, especially using low-power transmitters. At that time you could receive very few channels and that only in small islands.
In the meantime terrestrial TV here in Germany uses DVB-T exclusively and only in the lower UHF range. Therefore the old VHF III band got free for DAB/DAB+. But to this day DAB coverage is very spotty.
If you look closely at my Avion DRM radi findings here (https://swling.com/blog/2016/01/alexander-reviews-the-avion-av-dr-1410-drm-receiver/) and scroll down to the 7550 kHz screenshot you find circled 1 and 2 under the DRM logo. These are the two programs between you can select.
Here in Germany the signal quite often is good enough so the receiver does not lose sync for 10 min or more.
The sorry thing about All India Radio is the bad audio quality: They cut at 3 kHz and have quite some clipping, besides some hum from time to time.
Compare it to DRM signals from the BBC Workd Service.