Kmagrill said:
The unanswered question still remaining is:
Within the MW AM band, is there any technology or variant that might offer better promise for the long term prospects of AM broadcasting, other than migrating to VHF?
Can the positives of HD overcome its limitations? Personally, I have no idea, but at this point in the discussion, I see nothing tabled (yet) for the AM MW band that sounds likely to be better than HD. For all of its warts, HD does offer (arguably) higher fidelity which has been elusive previously. Stereo, while not critical (IMHO) is also offered by HD.
If nothing can be presented that works better in this band than HD, are there improvements that could be made?
What about the possibility of using an asymetrical digital modulation system to limit the power in sidebands that might affect close adjacencies?
Should HD stations consider tightening their analog signals to 4kHz or 3.5kHz to make more room for the digital carriers, thereby reducing the amount of necessary outer sideband data sent?
If that won't work, what would the risks/benefits be of identifying the HD stations with adjacent channel conflicts and offering them a reduced power, fully digital frequency to go along with their analog channel? Could the band be repacked so that, rather than operating within the adjacent channel mask, digital HD channels got their own separate channels on something like the expanded band?
I am suggesting no particular course of action here, but hoping others will take the ball and advance it with better ideas.
Answer to 1 - yes, there is. C-Quam. Not the best analog stereo technology, but viable because receivers exist. All iBiquity has to do is claim they have an improvement to HD radio, call C-Quam and / or AMax "HD AM version 2" or something, and roll it out. A lot of existing HD radios decode it. It is a software change for the others.
Answer to 2 - I know you HD advocates think DX'ers are a throwback, perhaps Neanderthals in disguise living among us, throwbacks, outmodes, delusional. But if you will listen for once, I will say it again: my tests on HD-AM using the best DX techniques that would give it every chance to succeed - after all, it is something new that offered the potential for something really nice for consumers, an AM band filled with stereo music again instead of the pitiful collection of ethnic, foreign, talk, and sports on AM now. It is no wonder the AM band is dying. A band with sound equal to FM would benefit everybody, especially if format holes in music like smooth jazz, oldies, classical, Christian rock, etc. could find a home on AM. So I am pre-disposed to want an improvement like digital AM. But - again, giving the technology every chance to work, I can truthfully say the results are dismal. Less than 10 mile range with HD on one station, 290 mile stereo range with C-Quam on the same station prior to conversion. On a WALKMAN. On another station, about 30 mile HD range, as opposed to 330 mile range - again with a walkman. I have never had a successful decode of HD at night, in spite of the analog being clear and interference free. When I do get stereo decode, it is curiously distorted, high frequencies translated in frequency lower, etc. Positives for HD-AM? Only theoretical ones that are not realized in the real world. I wish it were different, but those are the facts. I used as scientific a method as I could, going into the test with no preconceived notions. I suspected the worst going into the tests, and the reality was even worse than my worst fears. HD-AM is an epic engineering disaster. My theory as to what went wrong - too much susceptibility to interference on adjacent frequencies. Too many stations on the air in the US, plus absolutely no regulation of interference producing devices. Both problems existed decades before HD-AM was even proposed, and both have accelerated during the roll-out. It is time to cut the losses and go back to something that works - like C-Quam - while the industry still can (before it bankrupts itself and AM stations on HD-AM).
Answer to 3, yes, there are improvements that could be made! Re-allocate HD - AM stations - make a portion of the upper AM band HD - only. Super power stations in the HD-AM band so they can overcome interference and penetrate buildings. NO protection outside the city of license. Make the channels 30 kHz wide so adjacents from other cities don't wipe out the sidebands locally. I think HD AM would work under those conditions, but there are a lot of unknowns like how skywave on co-channels would affect it at night. But it has a shot at working - a better one than it does now.
Answer to 4 - assymetrical sidebands. From what I can tell, there is a glut of stations in the US, to the point of being ridiculous. You might improve a few situations during the day, but at night every single frequency is a cacophony of stations mixed together - it is a great leveler of playing fields which guarantees about the same ridiculously high level of interference on each sideband. I don't think a daytime assymetrical sideband solution even has a chance at night. Too many stations running too much power.
Answer to 5 - limiting bandwidth. This has been the dream of DX'ers for decades, eliminate splatter from first adjacents. The problem is, stations don't give a darn - especially brokered ones. We have a local here - KEYH 850 - that broadcasts somebody talking a lot of the time. The sound is horrible with a high level of hum, and unfortunately - even though it is speech - there is a lot of high frequency noise. I hear this same type of poor quality on a lot of the brokered religious stations. The preachers bring in tapes recorded on poor quality cassettes - the recorders plugged into church sound systems that have never been set up right - yet the tapes are broadcast with dolby mis-adjusted and pumping out high frequencies over AM stations, clicks, pops, static, hum, noise from who knows what source. You tune in a first adjacent, and you hear levels of high frequency splatter you never thought could exist in the program material on the station. Brokered formats, marketing, high school sports, you name it and it is the same story. Now there are unfiltered MP3's on the air with sampling noise splattering on first adjacents. It is an awful situation. Federally mandated low pass filters on ALL - and I do mean ALL stations would stop most of it, but you are going to encounter stiff resistance from small stations who claim they don't have the money to clean up their audio act. Even a station that actually shows up in ratings like KEYH may have the money to do something about their awful audio, but don't care to do it. Stations don't care, they don't have to, the FCC has no enforcement power over audio quality, so your 3.5 to 4 kHz brick wall low pass will never happen. Some stations purposely splatter so they get your attention as you tune across the dial - I was told this years ago by the operator of a Spanish language station, who took pride in the fact his station splattered almost 40 kHz up and down. He claimed his listeners actually liked the distorted audio on his station so he purposely overmodulated to clip it.
Answer to 6 - second frequencies for HD-AM. What is needed is LESS stations on the AM band, not more! The original FRC was formed to PREVENT the high levels of interference produced when stations were on the same frequency. The FCC abandoned that mandate, we have AM anarchy as it is. We could get rid of 90% of the AM stations in the US and still have unacceptable levels of interference on some frequencies. The FCC has not done its regulatory job, and you advocates of HD-AM are the first ones that should be complaining about the number of stations preventing your system from working - not suggesting things to make the situation even worse. "Thin the herd" is a battle cry some HD advocates have been trumpeting, and I whole heartedly agree! There are too many stations, operating at too high power levels, and this dooms HD-AM from working. Let's fix the problems, not make them worse! I'd love to have an HD AM oldies station on the air in Houston. But it would do me no good if 4 Spanish language stations from over the border, combined with 25 English language stations all vie for the same frequency at night. It just wouldn't work. Stop the legalized jamming - THEN talk about ways to make HD-AM reliable.
), but you do need a reasonably multipath-free signal. I know of reliable reception of non-direct signals, at well over 100 miles.