Radio digitale a Roma: nuove frequenze per il DAB+

Importante novità per gli ascoltatori romani delle frequenze della radio digitale DAB, che nei prossimi giorni dovranno risintonizzare i loro ricevitori. Da domani 3 settembre, su Roma, tutti i programmi di Radio Rai in digitale: Rai1, Rai2, Rai3, Isoradio, GRParlamento, Fd4 e Fd5 in DAB+ passano sul canale 12b in Banda III.  Sarà il primo indispensabile passo per poter poi completare il mux dell'operatore pubblico con nuovi contenuti, quali i programmi locali (così come è stato fatto a Trento e Bolzano) e - si spera - i programmi WR6, WR7 e WR8.

Quasi contemporaneamente,  il 4 o il 5 di settembre, Club DAB Italia inaugurerà la loro nuova postazione sul 12c, con i programmi nazionali in digitale di Radio DeeJay, Radio Capital, m2o, RDS, Radio Maria, Radio Radicale, Radio 24 - Il Sole 24 Ore, R101 oltre a 3 nuovi canali sperimentali Kc1Test, Kc2Test e Kc3Test ricevibili unicamente in DAB+. Come sempre maggiori dettagli si possono trovare sul sito dell’operatore di rete dab.it  

Restano invariate le coperture con i programmi nazionali di Euro DAB (Radio Italia SMI, Radio Padania, RTL 102.5 Cool, RTL 102.5 Rock, RTL 102.5, RTL 102.5 +, RTL Classic, RTL Groove, RTL ItalianStyle, RTL ViaRadio, RTL Guardia cost, RVaticana Ita) e quelli locali sia di Radio Vaticana (RVaticana Italia, RV Eur. Service, RV Eur. Service+, 105 LIVE L-BAND, 105 LIVE+ L-BAND, RETE ROSSA +,RETE VERDE) che di CR Dab (Radio Radio, Radio Subasio , Radio Suby, Radio Subasio +, Radio Kiss Kiss Italia, Radio Dimensione Suono Roma, Radio Dimensione Suono Due, Ram Power, Teleradiostereo, Teleradio2, Radio Montecarlo 2, Radio Studio 93).

Trovate la copertura, in costante aggiornamento, sul sito della nuova campagna promozionale della radio digitale in Italia, Digitalradio.it

BBC: crowdsourcing per misurare la copertura 3G

Il crowdsourcing al servizio della Quality of Service delle infrastrutture cellulari. Dopo il progetto Ne.Me.Sys lanciato da Agcom in Italia per la misura dei livelli di servizio delle reti Internet fisse dei diversi operatori, la BBC lancia una analoga iniziativa basata su una app Android (sviluppata da Epitiro, criticata per il forte impatto dell'applicazione sulla batteria degli smartphone). Basta installare questa app sul proprio telefonino Android per costruire una mappatura dell'intensità di campo generata dalle antenne 3G degli operatori mobili britannici. Una mappa possibilmente più attendibile (soprattutto nel confronto ricezione outdoor/indoor) di quelle normalmente pubblicate sui loro siti Web.

We're mounting an ambitious project to try to map mobile coverage across the UK - and, if you have an Android phone, you can be part of it. From today you can download an app which will record the signal you're getting on your phone - 3G, 2G or nothing - and feed the data back to our research project.

The UK 3G survey app has been developed by Epitiro, the firm behind Ofcom's recent report on mobile broadband speeds.

It will record phone signal data all the time the phone is switched on, and Epitiro is going to work with us to collect the results over the next month.

La cosa divertente è che appena diffusa la notizia, alla BBC sono arrivate le segnalazioni di una campagna di misura molto simile, ma su scala mondiale, effettuata da OpenSignalMaps. Anche in questo caso si tratta di scaricare una app Android (ma presto dovrebbe esserci quella per iPhone) per raccogliere dati che finiscono in un archivio centralizzato e vengono rielaborati in una mappa Google che mette subito in evidenza le aree in cui la rete mobile fa acqua.

Immaginatevi che cosa si potrebbe realizzare sviluppando analoghe applicazioni che sfruttino i chip per la ricezione dei segnali FM per tracciare mappe di copertura e interferenza!

Rumore, vero nemico dell'ascolto

Un articolo di RadioWorld online si occupa di un tema che noi ascoltatori di segnali molto deboli conosciamo, ahimé, sin troppo bene. Negli ultimi anni la soglia di rumore di fondo e interferenza sulle bande radio (in particolare sulle onde medie ma il discorso vale anche per l'FM) si è innalzata in misura abnorme. Fare un confronto storico, afferma l'articolo di RadioWorld, non è così facile perché mancano per il passato dati realizzati in modo uniforme e controllato, ma l'esperienza degli ascoltatori e degli ingegneri delle emittenti dice che la situazione è grave e che il rumore influisce negativamente sulle aree di copertura dei segnali.
L'articolo lo trovate qui, ne riporto solo un estratto e un paio di grafici molto eloquenti. Guardate in particolare quello sulla diminuzione dell'area di copertura in conseguenza di un aumento di 16 dB nella soglia di rumore di fondo e pensate a che cosa possa significare questa riduzione per una stazione locale. Gli effetti, dice ancora l'autore, si fanno sentire anche sulle modulazioni digitali.

[...]
Noise sources

Radio noise comes from a variety of sources, both man-made and natural, and the intensity varies on both a time-of-day as well as a seasonal basis. Frequency distribution also depends on the noise type.
The main two kinds of natural noise sources are atmospheric and thermal. Lightning is the primary atmospheric noise source and varies due to the proximity to storms and the time of the year. The noise amplitude caused declines of roughly 50 dB per frequency decade from 10 kHz to 10 MHz.
Atmospheric noise is the dominant natural noise source in the AM band. Atmospheric noise is more problematic at night because distant lightning storms can propagate long distances via skywave.
The thermal agitation of electrons causes thermal noise, also known as Johnson-Nyquist noise. Thermal noise is roughly linear with respect to frequency. Because atmospheric noise declines so dramatically with frequency, thermal noise is the dominant natural noise source on the FM broadcast band.

Man-made noise

Six broad categories of man-made noise exist: power lines, light dimmers, microprocessors and high-speed digital circuity, touch-control lamps, broadband over power lines and co-channel or adjacent stations.
Arcing across power line equipment often causes power line noise. Such noise declines in amplitude with frequency and typically is more troublesome in rainy and windy conditions.
Power line noise affects AM and FM but is most often noticed on AM because the recognizable buzz is demodulated in an AM receiver more readily than on FM. Power line noise is carried and radiated by the high-tension lines, compounding the problem.
Light dimmers made for home use incorporate thyristor devices that switch the AC line voltage with a very fast rise time. Unless effective filtering is used, these fast rise times can cause ringing that creates interference primarily in the AM band. Again, the AC power distribution serves as the antenna for the noise.
Huge advancements have been made in the speeds of computers, while at the same time there has been significant growth in the number of microprocessors and high-speed digital circuitry in so many other devices in regular household use. Since these devices include clocks ranging from a few kilohertz to hundreds of megahertz, even when effective shielding and filtering are used the cumulative effect raises the noise floor in the home, office and automotive environment.
The noise generated by high-speed logic has caused serious problems in AM and FM receiver design. Controllers used for receiver displays as well as decoding of digital radio modes create signals that are picked up by the adjacent receiver front-end circuitry, limiting the effective sensitivity of the receiver.
In the past few years, inexpensive touch-control lamps for the home have become available. These lamps may be switched on and off, or through a range of brightness levels, by touching a capacitive plate.
Touch lamps generally contain a free-running oscillator that changes frequency when the plate is touched. Unfortunately, these oscillators are also rich in harmonics and can radiate a wide frequency range.
In an effort to bring high-speed Internet access cost-effectively to a wide geographic area, some power companies have implemented technology in which high-frequency radio signals are carried on power lines. U.S. broadband over power line implementations have been limited to roughly 1.7 MHz to 80 MHz, according to the National Telecommunications and Information Administration, and would thus be limited to the spectrum between the AM and FM bands. However, this is not always the case internationally, and BPL is a significant source of noise to radio broadcasters.
Co-channel or adjacent stations are a source of man-made noise. The population of radio stations worldwide has multiplied several times in the past 20 years on both the AM and FM bands, as new services are authorized by governing bodies.
In the United States, in just the last decade, 2,000 more stations have gone on the air, according to the Radio World article “Number of Licensed Radio Stations Grows,” March 21, 2008. There are now a total of 14,253 AM and FM stations on the air, plus 851 LPFMs and 6,120 translators and boosters as of December 2008, according to the FCC, the latest information available.

Problema copertura: pregi e difetti del digitale

Craig Healy, DXer americano ha pubblicato un breve editoriale con il suo personale giudizio sulle potenziali conseguenze della controversa decisione della FCC, che il mese scorso ha autorizzato l'uso di IBOC sulle onde medie anche dopo il tramonto locale (una eventualità che, si tema, porterà a un inaccettabile aumento di interferenze alle stazioni lontane che operano sulle frequenze adiacenti). Attiro la vostra attenzione sul passaggio in cui Craig racconta di aver utilizzato almeno due apparecchi HD Radio e in base alla sua personale esperienza conclude che il "segnale digitale è molto fragile, la copertura possibile è pari ad appena un quarto di quella che un buon segnale riesce ad assicurare." Questa è una tematica che non mi stancherò di dibattere, per cercare di risolvere una volta per tutte i dubbi che riguardano la presunta superiorità dell'una o dell'altra forma di modulazione, analogica o digitale che sia.
Intanto, buona lettura delle interessanti osservazioni di Healy:

Editorial on the recent approval of HD Radio (IBOC) in the USA

On Thursday the 22nd of March, 2007 the Federal Communications Commission approved all facets of digital broadcasting in the USA. In particular, AM stations will soon be authorized to begin 24/7 use of their first adjacent frequencies for digital sidebands.

What this does is open the door to significant interference to all AM stations. A 50kw clear channel station can run a digital transmitter at far more power than would be authorized for any conventional station in that location on those two adjacent frequencies. It will be interesting from a rather perverse sense to see what happens at night..

I have had two HD Radios, and found that the digital signals are very fragile, and cover about half the radius (1/4 the area) of a good analog signal. Electrical noise from many sources like car ignition, light dimmers and bad wiring can easily disrupt things.

The programming is the real draw to a station, and HD Radio on AM will provide no change at all. A talk show in digital "high quality" is still a talk show. In the 35+ years I've been a broadcast engineer, I have seen a small handful of complaints about audio quality. These have always been when there is some correctable flaw, like a hum. Quality is not the issue and never has been.

I saw an interesting comment. Name and location deleted to protect the writer:
"The latest e mail from xxxxxx in xxxxxx said that the reason the big boys in the big markets are so pro IBOC is because they like the hash as it wipes out distant signals getting into their market. There is no way to stop skip, but if the IBOC hash wipes the signal out, then the locals will have to listen to their local station. Kind of like legal jamming. Considering that, then even if the public does not buy the radios, keeping the IBOC signal might be worth their while."

Jamming is illegal in many ways. If some entity has manipulated this process to allow it, then appropriate action should be taken to shut it off.

One possible result is many smaller non-IBOC stations refusing to drop power at night in an attempt to keep their current coverage area. Or, installing bigger transmitters to outright cheat to keep the coverage radius they had pre-IBOC. That would make a very interesting case, should it ever go to court. Two wrongs don't make a right, but when one of the wrongs is legalized, all bets are off.

Shouldn't the digital sideband powers be calculated by the same rules as used for analog signals? Just plopping in a new signal on a frequency without any regard for it's interfering effects is a recipe for chaos. No new station could be allocated today without a full allocation study. Why are these new digital allocations exempt? In effect, they are really two new stations in themselves.

What if there are unequal powers allocated for the upper and lower sidebands? For technical reasons, IBOC requires the two sidebands to be of equal strength to minimize interference to the analog signal. Didn't they see all this in the formulation stage? Or did they simply decide to ignore the obvious and forge ahead, oblivious?

There are some stations that have directional arrays that may never be able to be compliant with the specs for IBOC transmission. As a result, they will not be able to run it. Is it fair that some can and some cannot be digital? If digital-only operations are mandated, will these stations be forced to go dark? Is that fair to their communities? It would seem that many small town stations cannot afford the license nor the technical upgrades. Again, if digital is mandated, do these small towns simply lose their station, even if it is the only one? That seems grossly unfair.

Customers are staying away from these radios. Market penetration is very much below the radar. They hope to sell two million HD Radios by the year 2010. That's about how many iPods sell in a month.

Many years ago WLW had a project for HiFi radio. They made sure their transmitting plant was flat out to +/- 20KHz. There were receivers in that time that were up to that task as well. I would dearly love to hear that setup today, and compare it to the HD signal.

Instead of inventing this intrusive technology, they could have spent their efforts on DSP-based receivers to minimize impulse noise and other interference. A good DSP decoder can null out a coherent tone such as a 10KHz heterodyne without a negative effect on the audio. It could also compare the upper and lower sidebands to determine what would give the better sound. It could narrow the bandwidth to the most efficient point for best reception. And, the DSP decoder could look over a wide swath of spectrum to detect wideband noise and remove it. The technology is there, but they chose to ignore it.

Heck, if they could get such a good analog signal decades ago, what happened? What if a station today decided to use the mask designed for IBOC and implement a wideband analog signal? Would it be legal? How would that sound compared to the HD version,. assuming a good wideband receiver could be found? What if it even sounds better than HD Radio?

One of the significant problems of AM these days is the shielding effects of newer steel and concrete building construction. AM simply doesn't penetrate. Why did they think that overlaying a digital signal on the same band would penetrate these buildings any better?

A better overall plan would have been to embrace streaming technology. WiFi access is exploding, and WiFi-enabled iPods will soon be introduced. An iPod can do many things and at less cost than most single-purpose HD Radios. Streaming audio can have much better quality than even the best HD signal. Instead of HD1 and HD2, it is possible to have unlimited streams. The formats that can be streamed by a station are limited only by their resources and imagination, not some technical limit of their transmission medium. Reception of a stream is possible anywhere there's an internet connection, not limited to the coverage radius of a single transmitter. It literally is global. Power costs to run a stream are insignificant compared to a transmitter. No large towers, or arrays of towers are needed. Streaming is far more "green" than IBOC, if you care to look from that perspective. In terms of quality, variety and environment, HD Radio is obsolete right out of the box.

From a business angle, having the FCC mandate a proprietary system is unprecedented. All previous systems for anything were all open source. The technology to create a piece of equipment was there, every parameter. With HD Radio, none of these parameters are public, at least not enough that some clever engineer could roll their own. This is very unfair, and smacks of a monopoly. The whole HD Radio specifications should have been in the public domain. Were someone to reverse engineer this method, no doubt they would be hauled before a judge and significantly fined. All because some company has convinced the federal government that it has the only way to do the job. The parallel would be if the government decided that to drive on the interstate you had to buy a new Buick.

Recently it was announced that there may be pay-to-listen encrypted HD broadcasts. Could this be why they want the system proprietary? So nobody can legally write a decoder to bypass their pay scheme?

In conclusion, I'll relate a conversation I had with someone who has an extensive non-technical radio background. A local Clear Channel GM gave this person an HD Radio. It was tried, and shut off. Decoding the signal was very problematic even within the city grade contour of several stations. This person related to me that HD Radio was a bad joke and a complete waste of time. This was said without me even bringing up the subject. It seems to be a common "joe average" result when a non-radio person tries HD Radio. Too much effort to get a signal. They want to turn it on and get flawless audio, just like their iPod. It doesn't happen, so they simply return the radio for a refund saying it "doesn't work".