02 maggio 2008

Test in Alaska per il DRM?

Digital Aurora Radio Technologies, di Delta Junction, località a 200 km da Fairbanks, Alaska, ha chiesto alla FCC una licenza per operare in modalità sperimentale sui 5, 7 e 9 MHz in DRM (Digital Radio Mondiale). L'idea è quella di coprire, col segnale digitale, l'intero Stato dell'Alaska. A scoprire la cosa è stato Bennet Z. Kobb, autore di 26MHz.us, un interessante blog americano focalizzato sull'uso del DRM per copertura locale. Kobb ha messo online un altro servizio molto interessante, un feed RSS direttamente agganciato al sito della Federal Communications Commission, dove vengono pubblicate le richieste di licenze per l'attivazione di servizi sperimentali nelle varie porzioni di spettro regolamentato. Potete sottoscrivere il feed direttamente, all'indirizzo feed://feeds.feedburner.com/exrs oppure dalla pagina dedicata da Kobb, Radiospectrum.info. Qui per esempio c'è il testo della richiesta presentata da Digital Aurora.
Ancora non si sa se la FCC concederà l'uso di queste frequenze delle onde corte. E sempre ammesso che lo faccia non si sa se la stazione sperimentale sarà mai operativa. Perché in Alaska qualcuno dovrebbe essere interessato al DRM quando le zone abitate sono comunque coperte da onde medie e FM? Sempre scorrendo il blog 26MHz.us ho trovato anche un aggiornamento, come sempre piuttosto vago, sul ricevitore multimode WR608 della ChengDu New Star Electronics, costruttore cinese che aveva presentato il prototipo in occasione di IFA Berlino 2007. Per ora si tratta della solita chimera, ma è piuttosto interessante perché il WR608 utilizza silicio disegnato dalla britannica Mirics, un chip maker "fabless" che adotta l'approccio ASIC per la creazione di front-end specializzati multistandard analogico-digitali (dalle informazioni che ho raccolto ChengDu implementa la successiva decodifica DRM su piattaforma ARM). L'idea di un piccolo ricevitore multifrequenza e multistandard è molto allettante, ma tanto per cambiare si parla di disponibilità nel "near future". Un futuro continuamente rimandato, mentre le perplessità nei confronti dello scarso rendimento del DRM in condizioni propagative ionosferiche non diminuiscono affatto.
Alaskan DRM Experiment Proposed

Apr 29, 2008

Digital Aurora Radio Technologies of Delta Junction, AK has applied to the FCC for authorization to experiment with statewide DRM in the 5, 7 and 9 MHz shortwave bands.
The FCC has assigned the callsign WE2XRH to this station, but its license was pending at the time of this writing. Delta Junction is approximately 130 miles southeast of Fairbanks.
"The ultimate goal of this project is to provide a terrestrial digital radio service to the citizens of Alaska," the company said. "In general, the population of Alaska is underserved with respect to the ability to have a high quality, reliable public radio audio service. This is especially true for sparsely populated areas of the state."
Digital Aurora would perform propagation, S/N, field strength, bit rate and audio quality measurements over a two-year period. The signals will be contained in a 10 kHz channel, but the test may include a wider signal to investigate the impact on broadcast quality and "expanded digital capabilities."
Transmissions will be coordinated with the High Frequency Coordination Conference (HFCC).
"It is clear from the coverage contours that nearly all of the energy is concentrated for reception in Alaska," the company said. Major parts of the planned experiment will be to investigate how well the propagation predictions reflect field conditions and how low the transmit power can go below 100 kW without jeopardizing coverage in some parts of Alaska.
A unique element of the proposed station is its use of government surplus over-the-horizon (OTH) radar transmitters. Tests by the OTH system manufacturer, Continental Electronics, demonstrated the capability of the transmitter to broadcast DRM with "excellent performance characteristics" and within the spectral mask recommended by the ITU for this mode.
"An Alaskan experiment will fill a gap in assessing the performance of digital terrestrial shortwave broadcasting in the difficult high latitude environment," the company said.

2 commenti:

Andrea ha detto...

Bennett Kobb (che mi dice di aver studiato italiano al liceo!) mi invia un gentilissimo messaggio in risposta alle mie osservazioni. Giustamente Bennett osserva che negli Stati Uniti le onde corte non si possono utilizzare per servizi trasmissivi "domestici", il segnale deve essere diretto all'estero. Il che rende un po' più problematico l'accoglimento della richiesta di licenza presentata dalla società "alaskana". Ecco il messaggio che ho ricevuto:

Thank you for your article "Test in Alaska per il DRM?" 02 May 2008.
You are correct that it is not known if our FCC will grant a license to the Alaska DRM experiment. It is unusual that the station has a callsign but has no license yet.
Even after the experiment ends, it will still be necessary to ask the
FCC to permit SW DRM stations to be designed, built and operated for
domestic U.S. audiences. That is a complex legal process.
Such broadcasting is not allowed today because of World War II-era
regulations that have never been seriously revisited. Privately owned
U.S. SW stations must broadcast to other countries, with at least 50 kW AM power (or 10 kW DRM).
Of course it is OK for U.S. listeners to hear the station. But it is a waste of money and power to build a station for foreign audiences if
you just want the U.S. audience. So all this must change.
You asked why SW DRM in Alaska when the state has MW and FM stations.
But Alaska is very large (twice the size of Texas) and good terrestrial
radio is not available everywhere. The Alaskan experimenter benefits
because the transmitters are already in place (HF Radars no longer used by the U.S. military).
We also see a need for low-power local broadcasting at 26 MHz as you
know. The service could be like local FM. Most Americans are reached by MW and FM stations, but much of the programming is insipid and banal.
Meanwhile, still more want to broadcast but can't get MW or FM
frequencies.
So 26 MHz DRM can provide alternatives. This will also require FCC legal proceedings however.
We recently listened to Radio Vaticana and several other overseas
stations in DRM mode at the SWL Fest in Pennsylvania. The signals were excellent.
The broadcasts exist; the challenge is for receiver manufacturers to
create products. Manufacturers are waiting for inexpensive ASICs. These
have taken a long time to develop. They are also waiting to see what
their competitors do, and most of them are...doing the same thing.
Maybe the push will come from China, India, Russia.
Whether international or domestic, or both, perhaps there is still a
future for DRM.

Grazie

Bennett Kobb
Washington DC USA

Andrea ha detto...

Un ulteriore "chiarimento" (in italiano nel soggetto della mail) da parte di Benn:

"Il che rende un po' più problematico l'accoglimento della richiesta di licenza presentata dalla società "alaskana"."

The U.S. prohibition on purely domestic shortwave broadcasting [FCC Rules Part 73F] need not apply to stations in the Experimental Radio Service [FCC Rules Part 5].

The purpose of the proposed experimental station is not to broadcast programs to audiences but for test and measurement only. It really is intended for Alaska.

After the experiment ends the FCC will likely be asked to drop the domestic prohibition in our Part 73F.

Nota bene:

People frequently say that the U.S. SW stations "ignore" the prohibition. The FCC does not seem to closely monitor the stations for
compliance with the old programming rules.

Most of the stations are religious. The FCC does not want to get involved in religion.

But FCC does require that stations be planned, constructed and inspected to comply with those rules. FCC assigns them schedules/frequencies for outside-U.S. coverage.

Benn