Radio, FM digitale, USA: IBOC, Ibiquity e NPR chiedono l’aumento di potenza

I proponenti del sistema di radio digitale HD Radio affermano che tra i motivi dello scarso livello di accettazione commerciale c’è anche lo scarso livello di potenza del digitale fissato dalla FCC per evitre le interferenze tra stazioni.

Ne dà notizia, come sempre, Radio Passioni, che precisa che "HD Radio/IBOC è un sistema ibrido che trasmette sia le componenti analogiche sia quelle digitali. Queste ultime però devono essere trasmesse a bassa potenza per evitare interferenze con le porzioni analogiche e con le altre stazioni. Ora come ora il livello di attenuazione delle portanti digitali rispetto alle analogiche è di 20 dB, pari all’uno percento della potenza di tramissione analogica. Non abbastanza per ricevere un buon segnale all’interno delle case, dicono a Ibiquity. Da tempo l’organizzazione chiede alla FCC di autorizzare un aumento consistente di questo limite, pari a 10 dB pari o dieci volte. Oggi è arrivata la notizia dell’accordo di compromesso raggiunto tra Ibiquity e National Public Radio, che ha anche svolto uno studio in cui si analizzano le interferenze causate dai nuovi eventuali livelli di potenza dello spettro digitale di un segnale IBOC, Advanced IBOC Coverage and Compatibility Study. In base all’accordo i due organismi chiedono alla FCC di autorizzare le stazioni della rete NPR, un ente sempre molto aperto nei confronti della radio digitale e 2.0, a un primo aumento dei livelli da -20 a -14 dB. Sei decibel equivalgono a un aumento di potenza di quattro volte. Ci sono tuttavia molte perplessità sul reale impatto di una decisione di questo tipo sull’ascolto delle emittenti non digitali e sulle autointerferenze, cioè i disturbi che una porzione digitale può indurre nell’ascolto delle componenti analogiche dello stesso broadcaster". La situazione viene riassunta bene in questo articolo di RadioWorld.
 
NPR and IBIQUITY STRIKE DEAL ON HD RADIO POWER INCREASE
 
Blanket 6 dB increase, interference safeguards recommended to FCC; higher power levels possible
 
November 5, 2010, Washington, DC; iBiquity Digital Corporation and NPR announced an agreement for managing an HD Radio power increase that will significantly improve reception of HD Radio signals. The two organizations are jointly presenting their recommendations to the FCC today and encouraging the Commission to move to adopt the power increase quickly. “We are delighted that the radio industry is now poised to push this technology ahead together. We’ve found practical and balanced solutions that will greatly improve reception while limiting interference to existing analog operations,” said Bob Struble, President and CEO of iBiquity Digital Corporation. The agreement proposes that the Commission authorize a blanket 6 dB increase for all commercial and non-commercial radio stations’ digital power from the current level of -20 dBc to a power level of -14 dBc; this is four times the current power level. NPR and iBiquity consulted with a broad spectrum of commercial and noncommercial stations over the last few weeks, and identified several conditions and criteria to manage the power increase process. These conditions were informed by NPR Labs recent field research, “Advanced IBOC Coverage and Compatibility Study,” filed with the Commission earlier this week. Conditions of the blanket increase included commitment by iBiquity and NPR to additional enhancements to the HD Radio system. The development work of the two organizations will focus on single frequency networks to fill gaps in digital coverage, asymmetrical digital sidebands to reduce the potential for digital interference to short spaced first adjacent analog stations, and low bitrate codecs and conditional access crucial to moving radio reading services into the mainstream of digital radio broadcasting. Notably, the two organizations offered an approach to additional power increases beyond a 6 dB increase, depending on spacing criteria and conditions that limit harmful interference, and initial models suggest most stations will be able to exceed 6 dB. Mike Starling, Executive Director of NPR Labs, said “We are optimistic about the future of HD Radio broadcasting, and eager to continue to work with iBiquity on the developments that will make this power increase work to everyone’s advantage – stations, listeners, and receiver makers”. "I am thrilled that a workable and efficacious compromise has been agreed to on this extremely important and controversial issue," said Milford Smith, Vice President of Radio Engineering at Greater Media, Inc. "Replication of analogue coverage by the new, digital service is absolutely critical to the continued successful roll out of HD Radio™ technology". iBiquity and NPR encouraged the Commission to act on unresolved complaints in cases in which interference is shown to cause a problem. The agreement also proposes a series of steps drawn from the current AM rules for interference to be applied to qualifying and limiting harmful interference with analog at the 6 dB increase level (-14 dBc). These steps would remediate harmful interference from any stations increasing power above the existing -20 dBc power level.
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