L'altro giorno ho pubblicato un commento "moderatamente ottimistico" sugli effetti dell'autorizzazione a trasmettere segnali IBOC in onde medie nelle ore notturne negli Stati Uniti. Nell'articolo di The Local Oscillator si parlava proprio delle posizioni pessimistiche di Barry McLarnon, che risiede a Ottawa. Ecco il suo parere a poche ore dall'entrata in vigore del nighttime per HD Radio, previsto per il 14 settembre sulla East Coast. Sarà davvero il tramonto del DX in onde medie per gli appassionati d'oltre Atlantico? Se l'impatto sarà davvero così negativo, il suggerimento è: fatelo sapere alle stazioni radio interferite. Lamentatevi, "non fatelo in veste di DXer, ma di semplici ascoltatori," avverte Barry. Niente maleducazione, niente comizi anti-IBOC. E se avvertite un degrado qualitativo anche nel segnale della stazione interferente, segnalatelo. Chisà se basterà. Se a essere disturbati seriamente saranno i bacini allargati che le stazioni notturne possono sfruttare pubblicitariamente, è possibile che ci sia una levata di scudi da parte dei proprietari di queste stazioni. Ma c'è il forte dubbio che i disturbi siano percepibili solo nell'ottica un po' distorcente del DXer, peraltro già rassegnato all'incremento dei rumori. Coraggio.
A few thoughts as nighttime IBOC operation looms later this week...
Digital transmission has some advantages, but the hybrid digital system is a lousy fit for the AM band. Aside from the cost of conversion for the broadcasters, there are indirect costs associated with damage to analog services, both for the IBOC players and for those staying on the sidelines. The broadcasters have never had a clear idea of these indirect costs, since iBiquity, the NAB, and other IBOC proponents have always downplayed the problems. Now the rubber starts to hit the road, and to understand what they've gotten into, the broadcasters need to get feedback from their audience... lots of it. Come 9/14, let the interference complaints flow, but keep a few things in mind:
It should be obvious, but it bears repeating: you are reporting interference in the context of being a radio listener, not a DX'er. Keep it polite and to the point, and omit the anti-IBOC diatribes.
Complaints should go to the station being interfered with, not the station(s) causing the interference. There are a few exceptions, however. If you feel that an IBOC station's own digital emissions have degraded their analog signal quality, you should let them know. Or, if you have reason to believe that their IBOC equipment is malfunctioning, you should contact them, but make sure you're on firm ground before you do so.
Keep in mind that interference complaints are more likely to be taken seriously if they affect reception in or near protected contours. The first question to ask yourself is whether the reception is by skywave or groundwave. Only the Class A stations on the "clear" channels have protected skywave service, so complaints about interference to skywave signals will likely fall on deaf ears unless one of those stations is on the receiving end of the interference. If in doubt, you can check a station's class using sites such as fccinfo.com or radio-locator.com. Of course, some of the large market Class A's have little or no interest in skywave service, WOR being a prime example. At the other end of the spectrum are stations such as WSM that still have big skywave audiences, and thus should be more receptive to interference reports.
Some folks argue that AM skywave service is going the way of the dodo anyway. Perhaps they're right, but IBOC definitely does not just affect skywave reception. We all need to take a close look at IBOC interference to our local and semi-local stations that are receivable by groundwave at night. The difficulty here is to assess whether your location is in a station's nighttime protected contour, which is defined by something called the Nighttime Interference Free (NIF) contour.
NIF contours are based upon calculations, but unfortunately, they are not generally documented anywhere that is accessible to the general public, nor is there any free software available to do the calculations. My advice: don't worry about this arcane stuff. If you get normally get good groundwave reception of a station at night, and it becomes significantly degraded after nighttime IBOC starts, then you should report it to them. Let them decide whether your reception problems merit any action on their part.
If you want to get a very rough idea of a station's nighttime groundwave coverage, you can try looking it up on the radio-locator site. The red contour line is an approximation of the 2.5 mV/m contour. Except for the Class A stations, most stations will have a NIF contour that is somewhat smaller than this (in some cases, a LOT smaller). But don't get too hung up on the contours at this point... if you had decent reception before IBOC, and it goes seriously downhill after nighttime IBOC starts, then it's worthwhile reporting it.
Remember also that a recording could be worth a thousand words. A short audio clip of the interference could be a valuable addendum to your interference report. If you're keen, and have some inkling of which local stations might be interfered with, it would be worthwhile to make some recordings this week, so that you have some "before" and "after" comparisons available. The stations themselves should be doing this, but I doubt that many will!
Lastly, it should be noted that not all of the current AM IBOC stations (223 at last count) will begin 24/7 IBOC operation on Sept. 14. Some will have issues to sort out with automation, bandwidth of their night array, and so forth (and some of them, fortunately, are daytimers :-). The stations that do not have to change facilities at night are the most likely to keep it rolling through the night on 9/14. So, it will be important to keep track of which stations are actually running it at night, and to that end, I've added a column to the table on my AM IBOC page (http://topazdesigns.com/iboc/station-list.html) to show nighttime status. I encourage everyone to report the status of the IBOC stations they can hear, either on these lists or, if you prefer, directly to me.
Let the beta test begin!
Barry
Nessun commento:
Posta un commento