Many thanks to SWLing Post contributor, Mangosman, who shares the following review:
DAB+ digital audio/FM receiver and Bluetooth Audio Player with 2.4 inch LCD Display
by Mangosman
Digital Audio Broadcasting with improved audio compression and error correction is called DAB+. I have had this radio for a few years.
Retail in Australia DAB+/FM radios are generally double the price and more. There has only been one model of DAB+/FM/AM radios which is now no longer trading.
This is a size comparison, the sound is very clear and is surprisingly good on music as well, despite having such a small speaker. Even at maximum volume there is no audible noise or distortion. The stereo program HE AAC compressed and FM and Bluetooth and is available on cabled headphones. Such a small speaker cannot produce much in the way of bass, but it is present on headphones. Since DAB+ is a pure digital system, there is, full stereo, no noise as the radiated signal deteriorates, until the receiver mutes when error correction fails. The radio has a 400 mm long telescopic antenna.
On FM this receiver will decode Radio Data System data, I have had more sensitive FM reception.
This is the most sensitive DAB+ receiver I have owned. I am also currently also using two BUSH clock radios. I also have used older headphone radios, but push buttons and headphone sockets haven’t been very reliable.
This screen shows a full colour album cover which can fill the screen and title. Smooth FM is the broadcaster’s name because it is simulcast in some other cities on FM and DAB+. The indicators on this screen are level of battery change, muting, stereo indicator, when decoded and the signal strength.
Not shown are screens showing signal strength and error rate, tuned frequency and the technical characteristics ie the bit rate of the transmission.
Tuning is by on installation, a scan of the full band, where the receiver stores the frequency and ensemble names shown to the left. Then the tuning buttons select from the screen shown.
ABC & SBS share one transmitter and transmitter channel frequency. There are 18 programs on that frequency.
On another transmitter, shares 28 commercial programs (including Blender Beats) as well community broadcasters.
Only 2 of the above programs are HE AAC audio compressed and this radio can decode the stereo for the headphone output. The rest of the programs are HE AAC V2 compressed in stereo, however this radio cannot decode the stereo which means it does not comply with ETSI TS 102 563 V2.1.1 (2017-01). All of the programs including AM simulcasts are transmitted in stereo, are transmitted in stereo except a few speech only programs. Most Australian major cities have had DAB+ full time high powered broadcasts since 2009.
This radio has a rechargeable battery which lasts 8 hours driving a speaker and 4 hour recharge time. It also has a digital recreation of an analog clock when on standby.
Stereo outputs are standard in DAB+ decoder chips as it is in FM receivers, which in small radios is available in a headphone socket and combined for the speaker.
Please note: The only location for DAB+ broadcasts are in Europe, Australia and South Korea. The transmission frequency range is 174 – 230 MHz which limits coverage to around 100 km radius from a high power transmitter with a tall TV antenna tower. The USA uses that frequency range for TV channels 7 – 13.
Click here to check out this DAB+ radio on AliExpress.
Mangosman
Mangosman – I’m afraid that you misunderstand the principle of FM pre-emphasis. It doesn’t matter is the curve is at 50µs or 75µs – the results are the same. The receivers have the corresponding de-emphasis curve built into them as standard.
If you look at the spectrum – particularly the energy density versus frequency in broadcast music, you’ll see that the preponderance of audio energy is at lower frequencies. The pre-emphasis curve doesn’t affect the transmitted audio at all – the power density by the time you get to content at 15 kHz is minute compared to lower frequencies (even with your example of loud cymbals!). All the pre-emphasis does is increase the power density at higher frequencies on transmit, and the corresponding de-emphasis at the receiver flattens out the audio response again, but with the added benefit that the noise content (which is most prevalent at higher audio frequencies) is attenuated by the de-emphasis. The overall frequency response of the system is (effectively) flat from 20 Hz to 15 kHz.
However, there ARE some issues with FM broadcasting that have to be addressed by audio processing – firstly the frequency reponse has to fall off a cliff at 15 kHz, without the filters introducing level ripple or phase shafts in their passband. This is tricky, but can be achieved very effectively with op-amp filters (usually configured as “Elliptic” filters) and are usually done with gyrator circuits emulating inductors.
The next issue is level control. Typically, most radio stations employ a level limiter in their audio feeds. This introduces artefacts of its own, but careful design of multiband limiters can minimise these. Some manufacturers insist on using clippers for absolute level limiting, but these add distortion and harmonic products that can be unpleasant on the ear – that’s why “Orban”-processed audio usually sounds pretty nasty!
My “airchain in a box” product starts off with a gentle, slow-acting compressor to overcome gross differences in programme source levels, followed by a three-band limiter (a feedforward type with an analogue delay line in each channel effectively eliminating limiter attack time), then the audio frequency response (pre-emphasis) stage, feeding the 15 kHzlowpass filter then into the stereo coder, which is an oversampled switching type. Unusually, I employ “Walsh” synthesis, with stereo encoder switching multiplexers providing the sum (mono) component, the difference (S) component which is DSSC centred on 38 kHz, and a further Walsh Function synthesiser generates the 19 kHz sinewave pilot tone. Unusally, I also generate a second DSSC (S) component centred on 114 kHz – the third harmonic of the wanted S product – and this is added in the appropriate amount to null the third harmonic products of the 38 kHz DSSC multiplexing switcher. Higher harmonics are eliminated by an output lowpass filter (which is high enough in turnover frequency to avoid affecting the phase accuracy of the wanted products!). There is also a supplementary 57 kHz output that’s phase coherent with the pilot (and the missing 38kHz carrier!), which can be used to clock an RDS encoder, eliminating the digital noises sometimes generated by this system. Incidentally – each audio filter has overshoot compensation included, and all level control is done by means of PWM control which gives perfect channel matching and the lowest possible distortion.
The whole airchain is supplied in a 19″ 3U box, and has level indications (using LED bargraphs) on the front panel (for the benefit of radio station operators who insist on lots of blinking lights!). With careful adjustment by the radio station, this unit can be made to sound exceptionally good, with very low distortion, exceptional stereo separation, and no chance whatsoever of overdeviation. It takes line level balanced 600? audio inputs for left and right, and provides a low impedance (75?), high level (as much as 15V p-p) composite multiplex output.
I have spent many years designing broadcast equipment, and think that (finally) I’ve got it just about right!
Mangosman – DRM can work by ionospheric paths, but that’s a very different proposition to DAB / DAB+ broadcasting. Digital Radio Mondiale was originally designed as a way of enhancing shortwave radio, as achieves that in some cases. However, it can still be mangled by multipath – here in Europe, some of the southern European DRM transmissions are unusably scrambled by the time they reach northern Europe because of the multipath issues. The error correction in DRM does go some way to mitigating the situation, but isn’t a complete solution at all!
Braden – that’s partially true, but signal to noise ratio is proportional to power by wirtue of field strength, and both types of DAB require a clean signal (despite its much-vaunted “resilience” and “error correction”). A higher field strength also helps to overcome multipath issues (something else that wrecks DAB reception).
Any VHF signal at whatever power always goes to the horizon – it’s just that the field strength (and receiver quality) determines whether or not it’s useable!
The reason why COFDM modulation works so well is that the data is converted to thousands of closely spaced carriers. This allows the data to be transmitted faster. Then it means that the transmission occurs in bursts. The receiver will only accept the the bursts and ignore the reflected signals which will be delayed. HD radio does not do this.
Prior to sending the data parity data is generated mathematically. On reception the receiver uses the inverse of that formula to correct the errors. There is a limit to error rate and when exceeded the receiver mutes. We call it the digital cliff.
If you transmit at a higher power the reflected signals are also stronger. The stronger signals are important because the receiver has to determine which of either 2 or 32 levels of demodulated the signal is. The signals are in phase and 90 degrees delayed which doubles the combinations. Thus the Quadrature Amplitude Modulation has 4 bit and 64 bit combinations
The noise level of impulse noise decreases with frequency so generally the VHF bands are much quieter except where computer chips operate in the 200 MHz clock frequencies!
Australia transmits DAB+ from tall TV towers at 50 KW effective radiating power, so you get up to 100 km radius coverage area. In black spots the main signal is received, filtered amplified and reradiated. The filtering delays the signal so it will appear later just like a reflected signal.
SIRIUS-XM and HD radio offer great sound quality. And diverse programming. Pay or free, they both work very well. HD radio here in Detroit works very well. And it’s FREE. I still listen to and enjoy good old AM radio. FM is great, but seems to be taken over by sports and religious content. There are still great rock stations here and in Toledo. Unfortunately, it seems to be mostly satellite fed. Soon it will all be AI. Artificial intelligence.
Your American “HD” radio is that IBOC, isn’t it? I remember the IBOC trials when I was in the ‘States in the 90s, and we demonstrated that FMX gave better results in all cases than IBOC (and caused less interference!). IBOC was (and still is) horrible!
FMX was a brilliant tweak to ordinary Zenith-GE multiplex stereo. It gave an analogue FM signal greater resilience, allowed for reduced field strengths without degradation of the received signal, maintained compatibility with “ordinary” FM Stereo, occupied no additional bandwidth, and almost completely eliminated “picket-fencing” effects when listening from a moving receiver (in a road vehicle or a train). It just required minor modification to the station’s stereo encoder (or its replacement with an all-in-one FMX coder), and a fractional adjustment of the multiplex modulation level going into the transmitter, to ensure that 75kHz deviation wasn’t exceeded.
I still regret the demise of FMX. The only problem was that receiver manufacturers could only get the decoder ICs from two sources, and there were no cheap clones of the FMX decoder available yet. I designed two FMX encoder products for a certain well-known broadcast equipment manufacturer (I’ve also designed several conventional Zenith-GE stereo encoders, too).
Bizarrely – despite the widespread uptake of DAB / DAB+ – I’m still designing (Commercially) conventional FM stereo encoders and audio processors. There is still a very widespread requirement for good old analogue FM stereo!
Chris,
Why does the USA broadcast industry object so much to pure digital transmission? You did under pressure from the telcos convert TV from the horrible NTSC with the hue control to an all digital system called ATSC. The only countries to use it are in North America and South Korea. The rest of the world use DVB-T& ISDB and newer which rejects reflected signals much better than ATSC1.0. You are still designing equipment for FM because the Government will not organise a conversion to good pure digital radio, where the large sales of receivers drives down prices. FM is held up as some sort of saviour. It is not perfect either. For example all FM transmitters outside of the Americas use 50 microseconds of pre-emphasis which boosts 15 kHz audio by 15 dB, but since the USA started with 75 microseconds pre-emphasis you still use 18 dB high frequency boost. The reason why the rest of the world reduced the pre-emphasis was because the level of high audio frequencies in audio had improved with better recording technology. The end result now is that with loud cymbals for example the audio processor must dull down those sounds to prevent over modulation of the transmitter and therefore interference to other broadcasters, This does not occur in digital systems because there is no need for pre-emphasis because high frequency audio noise on reception is not a problem.
When an FM receiver gets reflected signals the distortion rises and the stereo separation reduces.
Receivers measure level of noise at around 16 kHz and when it is too high it blends the left and right channels back to mono to reduce the noise. None of this happens in pure digital signals.
In HD radio the power of the digital signals are less than 1 % of the analog power, so when the digital signals get too many errors the receiver blends back to analog then if it keeps deteriorating the mixing back to mono occurs.
Please do not use DAB as a standard. Every country except the UK has converted to DAB+ which not only has a better audio compression algorithm, the error correction is better. When there are errors in DAB is sounds like bubbling mud. DAB+ on the other hand keeps decoding correctly and then when the signal is worse it mutes. At this point FM from the same transmitter site is very noisy.
Lastly, there are now single chips which take the tuner output convert the received signal down to near zero frequency. They will then decode DAB+, DRM and if they pay the licence fees HD radio
I don’t know about the audio quality Sirius but much of it is delivered over the internet and not satellite.
The sound quality of HD radio may be greater than FM and is better than AM. However if there are multiple channels of audio, the bit rate is very low and the audio compression algorithm is kept private but has been superseded by at least 2 more efficient codecs which can produce better sound at much lower bit rates.
With DAB+ the broadcaster can specify the bit rate of each program is provided the total will fit in 1.08 Mbit/s. Australian broadcasters use anywhere between 32 – 120 kbit/s depending on program type.
There has only ever been 3 all digital AM transmitters on air and they are all very low power. There has been no all digital FM transmitters.
Since the digital signals in HD radio are carried in the transmission channels of other broadcasters the power levels are up to 1 % of the analog signal which means the digital coverage area is smaller than the analog area, and receivers blend back to analog as the digital error rate increases. HD2 – HD4 cannot do this and the receiver mutes. That happens in other pure digital systems but the digital transmission power is not restricted by interference to the broadcasters’ own signal or those of others
Looks a heckuva lot like the Majority “Eddington” model I bought for a European trip a few years ago.
https://www.majority.co.uk/radios/eddington/
Wow, that’s too bad. If it doesn’t work in densely populated country like the UK, it definitely won’t work in most of the US. Thank you.
Not gonna happen. With one stroke of the pen, all AM receivers become boat anchors. Great. Car radios too.
In Norway the Government and the only commercial national network had found their transmitter network of FM had reached the end of its economic life. So instead of replacing it with FM transmitters they put in DAB+ transmitters Nationally over the year of 2017. Then there was only low powered FM community stations left. They have no AM at all. During that time the population bought new radios or vehicle adaptors or new cars. After 12 months the ratings returned to their FM levels but with new additional program feeds which have also proved popular. Switzerland is doing the switchover next year to DAB+ just like most countries did analog to digital TV, even the USA because the telcos wanted the 700 MHz band from TV.
Here in Norway DAB Radio was introduced almost 25 years ago. Worked fine, but after only three-four years it was changed to DAB+. Very nice system, and the whole country is coverred with 39 channels.
Where I live we also have three local radios using DAB, and only one local radio left in the FM-band.
The authorities says that the FM band will close spring 2025.
I just love that kind of radio.
BTW the screenshot showing the radio front shows the norwegian state owned broadcaster…
I have this radio since ?3 years, and I suppose there is (still) no manual tuning?
Thxx!
Marc,
Manual tuning is a bit pointless when you stop on a single frequency and there are 18 or more programs to choose from. You would then need another knob to select which of those programs you wish to listen to in hex numbers!
Instead you do a scan and all available programs show. There are digital radio chips available which contain 2 tuners, one is for the sound and data and the other is continuously scanning looking for new transmitters and then they are added or deleted from the program list. This is most appropriate in vehicles.
Thank you for this feedback and information!
I don’t have a portable radio for the dab+ yet.
The antennas will be activated in my area by the end of June.
I am also watching the evolution of the discussion on DAB+ Emergency Warning Feature (EWF) / Alarm Announcement Switching (AAS).
Have a look at https://youtu.be/5ZHy2odu_X0
Mangosman
I wish this technology was available in the US.
Unfortunately TV channels 7 – 13 prevent the adoption of DAB+. There are other pure digital radio alternative systems which can work in the USA.
Yes, it said that in the article. But the DAB+ technology could be employed at any available frequency in the US. I would think lower frequencies would be better for the US, since those might have a chance of bouncing off the ionosphere and covering a much larger area, more like NVIS.
Braden – you really don’t want ionospheric reflection of digital signals! It will just further scramble an already easily mangled ditstream, making reception impossible. It would be even worse with a mixture of groundwave and skywave – the signals would have differing transit times, and as the Ionospheric Layers move, the reflections would cause fading issues too.
It’s a non-starter, I’m afraid.
Not true.
For example Radio New Zealand Pacific can be heard in digital radio mondiale in the West Coast of the USA. https://www.rnz.co.nz/international/listen. Radio New Zealand is buying a replacement high powered DRM transmitter, which is yet to come on air,
I have listened to DRM signals from the UK to a receiver in New Zealand.
I have not mentioned above, that DAB+/DRM signals are shuffled in time prior to transmission and then the receiver stores it and unshuffle it using the reverse algorithm. This spreads the errors in time to reduce the peak error rate and reception is more reliable.
Braden – DAB+ is only slightly better than the dreadful IBOC that’s inflicted on you in the USA.
Everyone praises its “clarity and low distortion”, but in reality, it’s pretty poor. Here in the UK, our original DAB / DAB+ services were reasonably good (albeit with some digital distortion), but the desire to cram in ever more services has resulted in radically reduced bit-rates, leading to audio “quality” that’s no longer tolerable. We have some music stations here that transmit in 64kb/s mono, and can’t understand why they have no listeners!
DAB / DAB+ Coverage is (generally) patchy, even in cities, and it’s largely unusable in the car (despite having a very good receiver), because of the blind spots and huge areas of the countryside without any coverage at all.
The vast majority of “radio” listeners are abandoning the off-air services of all kinds, and are now listening on-line. As we see it here, actual broadcast radio will die out completely in the next few years – especially as the mobile phone networks have better coverage than the DAB broadcasters! Practically speaking, I prefer to listen to radio programming uninterrupted – in the car – by using an on-line receiver.
Wow, that’s too bad. If it doesn’t work in densely populated country like the UK, it definitely won’t work in most of the US. Thank you.
Part of the problem is the decision early on that lower power transmitters were possible. This makes coverage patchy. There are also issues with multipath reception in cities – the signal can get completely mangled to the point at which the receiver mutes, so the programme appears to “drop out” – a common complaint with DAB / DAB+ services.
I’ve actually run rebroadcast DAB / DAB+ in tunnels, so have some experience of the ways in which it frequently doesn’t work too well, and I’ve been learning more about it by running my own (very) low power multiplex here in my house, using the Open Source DABMUX system that’s being quite widely used.
The processing overhead (and the consequent time delays) make DAB / DAB+ a non-real time medium. It’s all very disappointing!
Signals at that frequency are always line of sight, so a higher transmitter power wouldn’t fix the coverage issue.
The UK tried to push DAB as being hifi quality. Eventually it went to court. What happened was that they tried to jam as many programs into a single transmitter as possible. The low bit rate and MP3 low efficiency audio codec caused poor sound quality and extensive use of mono sound. Since there is now a second transmitter chain nationally many of those stations are using DAB+ as are local radio. The problem with DAB+ is it is very wasteful in band width. Using 1.5 MHz for 2 or 3 programs means that the transmitter power must be very low to prevent interference.
In 2009 Australia was the first to start full time high power DAB+ broadcasting. All programs are in stereo except for a few speech programs. The bit rate varies from 32 – 120 kbit/s and HE AAC V2 compression is used on nearly all programs. 75 % of new cars have DAB+ built in at no extra price. Australia is a big place and we only have 8 DAB+ transmission channels available because the rest are used by TV. As a result there is no DAB+ in country areas. Despite the telcos claiming near 100 % coverage they only cover 19 % of the land area. Since mobile phones use even higher frequencies than DAB+ they are even more patchy.
How long will the UK keep transmitting DAB for very old receivers. In 2009 our DAB+ receivers were modified UK designs.