HowardMBurgers said:
Hi Nick, Welcome to the HD radio discussion group! As you can probably tell by now, the forum has been pretty well occupied by those who appear to feel HD radio is on par with the apocalypse. Some feel they have been personally and financially injured by some AM stations implementing the Ibquity IBOC system, others who enjoy long-distance listening as a hobby, (Medium-Wave DX'ers) don't appreciate the interference to their hobby, while some appear to be older folks who think AM is fine the way it is. Really it doesn't take long to read between the lines.
I think you read too much between the lines. If anybody has given HD radio a fair chance, it is me. I own two HD radios. I listen to HD-2 channels on occasion, and listen to AM HD - when and if it actually works. I've given technical assistance to those trying to get HD radio reception - antenna selection and installation, etc.
That said - I also take a cold, hard look at the technology and am appalled at what I see. I have well documented the shortcomings of both the AM and FM systems, with tests as scientifically accurate as possible. I've torn into receivers to see how compatible they are with HD technology. I don't think anybody outside the advocacy groups for this technology have done more testing.
Yes, I do long distance listening. But for more than 40 years, it has not been a hobby. It has been the only way to get musical formats I want. Now, there is satellite and streaming, and you can bet that after 40 years I am good and tired of eating static because local broadcasters suck - now I can get static free satellite and streaming, and forget large antennas, modifying receivers to be more sensitive and selective, and the like. What a bunch of wasted time and effort over the years, all because local broadcasters can never seem to "get it right"!
As an independent voice, I have no financial stake in the success or failure of the technology. For what it is worth:
- I see assumptions, based on solving problems that simply don't apply to the majority of people.
- I see very bad engineering, systems not adequately tested before going public, a lot of posturing and denial when problems occur, ad hominen arguments directed at those who point out the problems, and intimidation. These are NOT signs that the system has credibility.
- I see poor marketing techniques that do not address the advantages to the consumer of the technology. If they want to sell HD to the public, they need to fire their ad agency and get another.
Specific technical issues: AM
(1) I have documented very well that most newly designed AM radios are inherently broadband, just because the manufacturer puts as little money into the IF section as possible, sometimes bypassing it with a capacitor making the only selectivity in the receiver due to the antenna and tuning capacitor. +/- 40 kHz IF bandwidth is commonplace. Given that wide of a bandwidth, the portions of HD signal occupying 10 to 15 kHz punch right through, and tiny speakers make terrific tweeters for those frequencies.
(2) The attempt to hide HD modulation by phase modulating it from 5 to 10 kHz is worthless, because no antenna system has flat phase response and a portion of the modulation gets converted to amplitude modulation. And any mis-tuning at all, which is very easy to do with cheap mechanical lashing on the tuning mechanism in cheap radios virtually guarantees that precise tuning won't happen - therefore more IBOC sideband hiss showing up in the audio of the radio.
(3) Ibiquity's test radios were a collection of 10 to 30 year old antiques, which primarily used the three IF can reference design which is no longer produced because it is expensive, takes up too much space on a PC board, is power hungry, and is not as reliable as single IC designs. The single IC reference design has dominated every new design done in the last ten years, if not longer. And older radios get tossed because the volume knob gets scratchy - "oops my radio doesn't work, I need a new one ---"
(4) The AM HD system is very prone to interference, causing loss of lock. The slightest bit of noise and the lock is gone - which effectively makes it useless at night, because every single frequency has multiple stations on it. The same interference susceptibility causes lock to be lost going under power lines or other sources of interference. This also presents a safety hazard to drivers - before they could hear the interference increasing and decrease the volume. Now there is an abrupt change from perfect clarity to very loud interference, something HD cannot alleviate.
(5) The low bit rate that has to be employed because of narrow channel bandwidth may be adequate for speech, but it cause strange aliasing effects on music, making it very unpleasant to listen to, something akin to a medium bandwidth internet stream.
(6) The digital sidebands are more persistant that anybody could have predicted, I have personally hear sideband pairs in the daytime over 1000 miles from the station, in remote rural areas - long past the point where the analog signal can be heard at all. Surprising, given the lack of robustness of the system maintaining lock, and given the power levels involved. Yet the sidebands persist, clearly audible. It is very obvious who the offender is, when sideband pairs appear - and no other HD station is on the air in the country.
(7) Nighttime HD sidebands are horrific. I have never heard WOR from Texas. Yet its sideband pair is there at night, and disappears when I null the radio in the precise heading of the WOR transmitter. No wonder multiple broadcasters are crying foul about interference with their station from distant HD stations, and no wonder stations owned by the same group shut down HD to avoid interfering with each other.
FM technical issues:
(1) First adjacent reception is not an issue near city centers or near transmitter sites, there simply aren't that many first adjacents existing. But the situation changes dramatically in suburbs, particularly in the East. First adjacents are commonplace, enough so that even NPR is backing off from wanting a full power increase. Some of those suburbs are sources of affluent donators, who are not eager to lose their first adjacent station, especially when the signal strengths are close to the same.
(2) IC makers have poured a lot of money into FM IC's, and new technologies such as adaptive IF make first adjacent reception much easier, if not commonplace. Stations that were previously inaudible now come through clearly. It doesn't take long for people to discover them, especially with the ill-conceived "stations between the stations" ad campaign - which encourage people to tune their radios to more distant stations.
(3) The entire duration of the HD FM roll-out has been in an era of unprecedented low solar activity. Solar activity is cyclical, and the next solar max is going to take place in 2012 or 2013. The presence of HD sidebands, which will propagate like separate stations, will produce unpredictable and probably bizarre results, with the analog portion of a station taken over by an HD station on the same frequency hundreds of miles away. This has already happened on a small scale, with numerous reports of strange and sometimes humorous switch overs. These will become commonplace, particularly if an ill-advised power increase is granted. People's annoyance threshold is very low - if OTA radio isn't reliable, there are an every increasing array of more reliable music sources.
(4) Carefully conducted experiments show that HD lock can be easily obtained using nothing but a dipole 70 miles from Dallas, and 84 miles from Houston. This is about the range that the stereo carrier is starting to be lost. Therefore, the range of HD FM is comparable to the range of stereo FM, at least in those markets. NO power increase is necessary or warranted - people who don't have reliable analog reception won't have reliable HD reception, and vice versa.
(5) A 10 dB power increase will do nothing to help HD in the fringes, where it is dropping out now. Fringe area reception is characterized by signal strength fluctuations of 60 dB. Given the lock time of HD, 10 dB will do little to alleviate the problem for drivers.
(6) The same large signal fluctuations exist near airports, causing problems as close as ten miles from the Dallas sticks, according to one report. I have personally heard the HD problem near airports - a plane files over and lock is lost. It doesn't come back reliably until the plane is far away.
(7) In spite of the claims that HD fights multipath, the wailing of listeners in hilly areas such as West of Boston leads to the inescapable conclusion that HD does little to fight multipath, lock is simply lost when multiple signal paths are present. I suspect the same will happen when skip occurs, or in first adjacent situations.
(8) A 10 dB power increase will do little to penetrate buildings. I used a spectrum analyzer to look at signal strengths inside a building. I saw a 10 dB drop every 6 to 8 feet away from the window. That is about one row of cubicles. Not a lot of additional listeners, who are probably defying their computer admin's rule against streaming as it is.
And so forth --- the list of problems goes on and on, the whole thing starting to assume the appearance of a conspiracy or a religion. As for me - the emperor has no clothes. HD myths - BUSTED. I'm an experienced engineer, not likely to make too many observational mistakes, and the whole HD thing is full of technical problems, factual distortions by the promoters, and a lot of posturing by the HD industry to keep from losing their financial shirt - which is probably inevitable at this point anyway. It has all the earmarks of somebody wanted to preserve some sort of share value, then bail out of their stock at the last moment before the defecation hits the rotary ventilation device.
OK- flame away - but do me the favor of telling me where I have made FACTUAL errors in my observations. I have no tolerance for ad hominem remarks and will ignore them.
