DRM broadcast (left) as seen via a KiwiSDR spectrum display.
Many thanks to SWLing Post contributor, Richard Langley, who shares this story by Hans Johnson at Radio World:
Can an App Solve the DRM Receiver Problem? (Radio World)
The Digital Radio Mondiale standard for digital broadcasting in long, medium, and shortwave bands offers the possibility to transmit audio, text and pictures.
A few broadcasters use DRM for both domestic and international transmissions. DRM’s largest problem is lack of receivers, especially affordable standalone ones.
Some listeners use an SDR, computer and free Dream software to receive the DRM signals, but this audience doesn’t make up the mass audience that broadcasters are looking for.
[…]AlgorKorea didn’t develop the apps with the intention of solving the DRM receiver issue. They developed them to resolve a problem with FM hearing aids used in classrooms.
So how do they work? The DRM+SDR version couples the popular and inexpensive RTL-SDR to an Android device with a USB OTG adapter.[…]
Click here to read the full article at Radio World.
There is a version of this app called DRM+SDR, which has been tested with an RTL-SDR v3 dongle. I tried it on my Android tablet. The DRM+SDR app only allows entries of HF frequencies up to 28MHz, so use of an upconverter seems to be precluded. In the link from the Korean manufacturer’s website, it states that it was tested using a strong received signal, probably from China. I think a strong aignal would be necessary if the app makes use of the dongle’s direct-sampling facility. As with other Android SDR apps I find an external USB hub is necessary to supply additional power to the dongle, otherwise the driver app stops working. I came to the conclusion that this app was unlikely to give satisfactory results, so I applied for a refund and am no longer using it.
Somehow this whole article and the discussion is messed up:
The referenced article contains a picture that has nothing to do with DRM as we know it: What seems to be a 2.4 GHz audio receiver of some kind is connected to the mic input of a smartphone. What should that be for? There is no RTL-SDR dongle anywhere. The audio receiver also has no power supply.
The discussion is messed up. too: The data does not come through the cell network but from the RTL-SDR dongle. Any DRM solution should work without any cell connecivity!
But a standard RTL-SDR dongle cannot receive below about 25 MHz! You need a specialized one that contains an up converter or you circumvent the tuner chip and directly feed your signal to the SDR chip.
The only valid point is the power supply: You cannot charge the battery while you listen to DRM stations because of the USB-OTG adapter blocking the USB socket. Some RTL-SDR dongles draw quite substantial power.
> “The referenced article contains a picture that has nothing to do with DRM as we know it: What seems to be a 2.4 GHz audio receiver of some kind is connected to the mic input of a smartphone.”
Not even that. The picture shows a Microchip MRF89XA devboard; a FSK/OOK data transceiver operating in the UHF ISM bands. https://www.microchip.com/wwwproducts/en/MRF89XAM8A
Nothing to do with DRM, except to pad out yet another slow news week puff piece…
I wish that posters would check their facts before posting.
http://www.RTL-SDR.com says “What is RTL-SDR?
RTL-SDR is a very cheap ~$25 USB dongle that can be used as a computer based radio scanner for receiving live radio signals in your area (no internet required). Depending on the particular model it could receive frequencies from 500 kHz up to 1.75 GHz. Most software for the RTL-SDR is also community developed, and provided free of charge.”
https://www.rtl-sdr.com/wp-content/uploads/2018/02/RTL-SDR-Blog-V3-Datasheet.pdf
The photo in the RadioWorld article shows the RTL-SDR module without the cover, it’s downconverted output is fed via a capacitor to remove any DC connection and a resistor as a load for the module.
The cabling is to split the mic input to the phone and the earphone output.
The RTL-SDR module must be separately powered using a USB connection.
> “The photo in the RadioWorld article shows the RTL-SDR module without the cover,”
Let’s be clear here, Alan. There’s 2 pictures in the article – one is of a couple of guys working at office desks, the other is a diagram that allegedly “shows how the DRM+ app connects to a phone or tablet”.
Look at that diagram closely. What you’ve misunderstood to be “the RTL-SDR module without the cover” is a board that’s clearly marked “MRF89XAM9A Rev. 1”, containing a chip that is marked with the Microchip logo and the part number “MRF89XA”.
FWIW, I provided a link to the MRF89XAM8A earlier, because all the pictures of the 9A module on the Microchip website have a shield over the components. Now, I know you’ve always relied heavily on press releases rather than actual research for your “knowledge” – so here’s a link to the datasheet of the MRF89XAM9A “915 MHz Ultra Low-Power Sub-GHz Transceiver Module” for everybody else:
http://ww1.microchip.com/downloads/en/DeviceDoc/75017B.pdf
I wish that posters would check their facts before posting…
Remember that phones are the most expensive way of broadcasting to a large audience both for the listener and the broadcaster. Mobile phones are a two way communications system in which the return path is virtually unused. Each listener has to be fed a separate signal. Broadcasting is a one way communications system which is common to all listeners.
Mobile phones are useless in an emergency because;
1. the battery goes flat due to having to transmit every 15 min the phone’s location and when the mains supply fails you cannot recharge it. Solar chargers don’t work at night or in lots of clouds which occurs in storms.
2. Phone, FM radio and TV is transmitted from the highest altitude in the area to get maximum coverage area. Hot air rises making these sites targets for fires. If the transmission tower is not burnt down, then the electricity supply will fail due to fire or wind damage.
3. If phones and smart speakers take over from radios, many people will loose there lives because there aren’t radios to give warnings.
The advantage of SW digital radio ie DRM is that you can site the transmitter well away from areas of cyclones, fires, floods and away from borders and cover the whole country regardless of size. DRM can transmit maps and indexed detailed text instructions along with sound warnings which can be targeted on the Emergency area and it will wake the radio even in the middle of the night and tune in to the emergency messages. This system is already working in India and has been tested in Indonesia which are both affected by large scale disasters like monsoons, earthquakes, cyclones and tsunamis.
Fortunately most vehicles have radios and a large battery. There are 2 million line fit DRM radios in India in a short time. They have 4 high powered DRM HF transmitters and 35 DRM very high powered Medium frequency transmitters
“This system is already working in India “,
“There are 2 million line fit DRM radios in India in a short time. ”
I live in India and I have no idea where and how I can get these DRM Radios
Can you help?
If you have an app on your phone you have a phone. If you have a phone, you aren’t likely to need/want SW radio. Try again, people.
Well, that’s not *necessarily* true… A lot of Africans have cell phones, but their data networks aren’t really robust enough, especially in rural areas, to support audio streaming. A lot of what they do is accomplished via more simple means like calling numbers and texting. I understand text money transfers are popular in a lot of the continent, because it doesn’t require a data connection or a bank.
So, there are plenty of places where people might have phones, but also have a shortwave radio because it’s simpler, the batteries last longer and is more reliable.