Quello che segue è un provocatorio articolo apparso su Radio World Online (rivista già citata a proposito del ricevitore IBOC Boston Acoustic). L'autore Jerry Smith propone un confronto tra l'AM digitale e un sistema, analogico, di AM stereofonica. Il risultato? L'AM stereo vince a mani basse quanto a costo contenuto e incremento dell'area di copertura del segnale, aspetto su cui IBOC è piuttosto debole. Qui tra i link di Radiopassioni trovate un riferimento a Wrath of Kahn, un sito realizzato proprio dall'inventore del sistema AM stereo descritto nell'articolo di Smith, Kahn PowerSide. Da tempo Lawrence Kahn va ripetendo che la vera alternativa alla presunta "qualità" dell'AM digitale è l'AM analogica stereofonica, che a differenza di IBOC non provoca particolari interferenze alle altre stazioni. Migliorare la qualità dei programmi è il primo ingrediente dell'elisir di lunga vita delle onde medie, seguito da una migliore qualità di trasmissione analogica e da ricevitori, analogici, capaci di ricevere meglio (a una frazione del prezzo di un apparecchio digitale). Ma dietro IBOC c'è un grosso gruppo di stazioni radio, Clear Channel, che delle concorrenti se ne frega. E ci sono anche un sacco di soldi in ballo. Anche in Italia è possibile ascoltare una stazione in onde medie stereo, Studio X da Momigno e un sito Web giapponese, Audio Cubes, consente di ordinare un piccolo ricevitore Sony compatibile, il modello SRF AX-15. Per saperne di più sulle onde medie stereofoniche si può andare su http://users.hfx.eastlink.ca/~amstereo/ mentre il sistema PowerSide viene descritto da http://www.hal-pc.org/~jsgil/AM-Stereo/ISB.Txt.
Commentary: Power-side Tops Fla. Engineer's List
Kahn System Enables Extended Listening Area and Increased Coverage in Interference-Prone Areas
by Jerry Smith - Radio World Online
We must prepare for the possible turns in the road that HD Radio could deliver to those of us depending on broadcasting for our Social Security payments over the next 12 to 40 years. I observed and tested the Kahn Power-side Clear in a Tampa-area radio station recently, comparing it to the HD signal on Clear Channel's WFLA(AM) at 970 kHz. Here are my observations.
Power-side is a system introduced by Kahn Communications some 20 years ago, which the company has coupled with new Clear technology designed to enhance the overall loudness on conventional narrow-band AM radios. The Kahn Power-side Clear system is the first step toward the Kahn CAM-D digital system, for those who prefer a two-step process to an alternative digital transmission system that immediately improves the signal and sound on conventional radios. We chose to start with the Power-side Clear package, capable of being upgraded to the CAM-D system at a future time. From all reports and sample airchecks of stations making the jump, the CAM-D package offers even further improvement to analog coverage and provides digital audio capability with no increased noise or interference to adjacent stations. Kahn introduced the CAM-D, developed over the past several years, when the first series of IBOC systems appeared in the marketplace exhibiting a multitude of technical artifacts. Both the Power-side Clear and the CAM-D system utilize the original brick-house military specs designs from the Kahn AM Stereo 84 rack-frame design from the mid-1980s. The company has done extensive work on raising the bar for louder and cleaner audio, even under adverse conditions such as power line and other re-radiating sources known to increase interference under conventional double sideband AM transmitted signals. By adding the Power-side Clear unit, audio delivered into the radio station's coverage area appears with increased loudness on conventional radios, with the added advantages of field tuning for distortion correction in the transmitter and associated RF tuning components plus a significant reduction in distortion from those annoying power lines and tall buildings.
Great ideas languish
The local station owner had been skeptical about purchasing Power-side, and we had no guarantee the system would fix our problems with adjacent splatter and critical hour and nighttime interference. We bought the box on my suggestion after more than nine years of discussion and searching for information. I am as happy as a Lotto winner about the results. Our coverage area in daytime and nighttime operation is estimated to have doubled the effective listening areas with the addition of the Power-side Clear unit. Power line re-radiation known to cause the muffling effect on the audio and increased static is now practically non-existent in areas formerly written off as noise-prone.
WFLA sounds very good on the new digital radios but seemed subject to interference far greater than its original analog signal once was. Overall WFLA does a very good job covering the market in analog mode. But its digital sidebands have effectively eliminated ABC's Orlando 990 signal in Sarasota and Lakeland along with the Salem 950 AM from Orlando in Lakeland, formerly strong markets for those two facilities. So while digital AM receivers are cleaner than conventional narrow-band imported radio receivers, the added digital splatter-noise is eliminating AM as a viable alternative outside of the 5 to 10 mV/m contours. Most quoted consultants now agree that nighttime AM digital is a dead issue; and most have determined that first-adjacent FM signals must have far greater mileage separation in the new digital experimental age. Tragically for broadcasting, our leaders are held captive to investment portfolios and their Wall Street perspective defining the cure for all technical and programming shortcomings as the switch to anything digital. Thus HD will be the sounding bell from the chief executives hopeful of saving their jobs for another decade until HD increases facility values or closes down half of the present facilities.
Meanwhile great ideas such as Power-side and the Kahn CAM-D digital system, which we now can confirm as improvements to analog performance while reducing adjacent-channel interference, will remain in the background, to be picked up by broadcasters trying to protect and improve their coverage footprint. I too now agree with the Kahn system approach to saving AM radio and the advent of CAM-D as a clear and loud alternative to other digital systems. Prior to these recent tests, I was unclear as to the benefit of the Kahn system for AM work. Now, without a doubt, the potential for AM improvements on bad radios and during critical and night hours have hope for anyone willing to invest the money for these inventions. And this approach is truly an in-band and on-your-channel system, raising the value of the protected contours of a radio facility, while the other digital system - measurably and by listener tests - definitely harmfully affects stations in the adjacent channel spectrum.
Raw deal
I know there are competent techs who do not like the Power-side system based on prior experience with AM stereo installations years back. I have visited a few facilities and interviewed those men; I understand their concerns. But this box really works. The only reason anyone would not like Power-side Clear would be improper installation. Most tech guys with a heart will admit they know little about AM facilities and even less about a trick box that requires an attention span of greater than 30 minutes. The Power-side Clear is only part of the Kahn CAM-D system. But we have spoken with users of CAM-D who just cannot believe the difference in going to the next level above the Power-side Clear update to CAM-D. Power-side is capable of extending listening area and increasing your coverage in areas populated with power lines and during various interference conditions. But there is the need to understand source material limitations when loudness approaches those levels with Power-side equipment. We face greater source material distortion control issues with digital and don't seem to mind the risk at all. The good news is Kahn Communications has experienced installation technical help to set up the Power-side Clear or CAM-D equipment. They don't leave you clueless in the dark about set-up and operation. Given that we are likely to be "stuck" in analog until the last generation of available foreground listeners gains admission to retirement homes, I welcome the addition of anything that can improve coverage and merge into digital technology without harming the next-door neighbors in the process.
Trolley effect
Consider what the Power-side package has done for our test station in Tampa, which had been suffering from the Trolley effect. The radio station was getting killed by high-voltage noise and control data signals from the city-owned trolley in downtown Tampa. With Power-side Clear installed, the noise is reduced to the background; it does not wipe out the audio and carrier as the trolley car passed us by. Our digital competitor has 10 times the RF signal at the trolley. With their recent digital upgrade they now get blasted by the transit system - which did not bother them at all in the past. So this product is something to watch, although I understand that most people, while having great respect for Leonard Kahn, would prefer more access and information to what CAM-D has to offer.
The Power-side package is less than $20,000 while the CAM-D is in the order of $40,000. And it's rather amazing to watch as broadcasters pick the lesser-priced box when in fact the folks who upgraded to CAM-D say their coverage increased even more and their sound became even more remarkable. For the sake of saving AM radio, it is worth offering this short-term tool for anyone who really wants to improve their AM facility. When I say "short term," I mean 40 years, at most. I have several new clients doing AM upgrades this year. I was skeptical about suggesting the addition of a $40,000 box to the package. Now it is at the top of the list. How could anyone not consider spending at worst case something that costs $3,000 a year over 12 years, or $1,000 over the next 40, to improve the coverage in areas where even the 50 kW signals don't tread? Mr. Kahn is our last action hero, for sure.
The author is a broadcast technical consultant specializing in AM, FM and TV RF systems.
Tags: radioascolto, radiofonia, radio, dxing.
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