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HD-AM, blame the engineers not the system

C

Carmine5

Interesting letter from an anonymous source. In essence the letter says that if the HD-AM is not working correctly for a station, blame the engineer setting it up.

A portion of the letter:

"HD installations often begin to go wrong with the engineer doing the installation. If that person doesn't fundamentally understand their entire antenna system, hasn't made all of the network measurements and adjustments necessary to even consider an installation, doesn't have the system FLAT (close enough doesn't work), and has older gear/short spaced towers, nearby AM transmitter sites that operate at close frequencies, hasn't created separate day and night settings, and/or hasn't done at least a few installations before, they are likely to have problems."

http://earthsignals.com/add_CGC/Letters/HD_Implementation.htm

Sounds like the planets have to be aligned at the proper instant for this thing to work. It also sounds like HD-AM wouldn't work on a di-plexed system.

C5
 
Yes, it's true. For the same reason cymbals and snare drums sound bad at lower bitrates in mp3s, MW simply hasn't ( at 50 khz) sufficient bandwidth to DEFINE accurately the various digital sidebands' states to give a reliable decode for the number of sidebands they've allocated.
Another problem is SLEW, and the problems encountered going from radiator propogation "wave speed" vs that in free air, and again back to "receiver antenna" propogation wave speed, .9 of that in free air, if I recall correctly. This "smears" the signal in a way most unkind
to the needs of digital signal reception. I am still amazed that the darn thing was ever proposed, much less accepted by the
fine folks at the FCC.
 
It's a valid point, as long as you ignore the interference HD-AM pushes onto other signals on adjacent channels, whether nearby or far away. AM engineering was, at least the way I was taught it years ago, as much about being a "good neighbor" as it was about transmitting the highest quality signal possible. The adjacent-channel interference issue should have been a huge red flag with the FCC, and instead it was ignored.
 
"Doesn't have the system FLAT?" "Has older gear?"

This kind of hogwash could only be written by a rabid HD promoter. I suspect Tom Ray, Cris Alexander or some other flat-earth HD'er. These are plainly preposterous statements.

Anyone with even middling AM-directional experience knows that "having the system flat" isn't a simple matter of twiddling the phasor controls or tinkering with the common point. The plain truth is that few AM-DAs have linear common point impedance simply because even the finest phasing systems, like those from Kintronic, aren't designed that way. Until the halcyon HD epoch such stringent design would only introduce massive and unnecessary costs. "Linear common point characteristic" is a nice theory but it is not a real-world AM broadcasting phenomenon - even in relatively new directional arrays (please excuse us for example, for having "older" 2006 gear which wouldn't work with HD either.) Factors affecting antenna linearity include tower height, frequency, power and even the real estate - remember that ground conductivity and nearby reflecting structures are as much a part of your antenna system as the phasor and ATUs are.

Witness WMVP (former WCFL) 1000 Chicago. They couldn't get HD on the air until last fall, and only after about a two-year rebuild of their DA system costing an estimated million(s) of dollars. Their "older gear" consisted of a recent phasor and new towers less than a decade old, yet having critical networks and very deep nulls which exhibited poor pattern bandwidth of no consequence to analog listening but fatal to "acceptable" HD operation. Then there was KDKA with its "Franklin" stacked dipole, where the halves of the nondirectional anti-nulling stick produced horrible HD self-interference on the analog signal. They were running a reduced 35kw on STA for the purpose of HD-tinkering for the better part of two years.

Talk to those engineering departments about "having the system flat." The suggestion that all you've gotta do is spin the phasor inductors for an hour or so, and - just like THAT! - you'll be all HD-groovy, is ludicrous. It's a little like arguing that you could have won the Indy 500 driving your 1971 Pinto if only you'd taken the trouble to do some appropriate engine tuning.
 
The system is inherently flawed from the top to the "envelope." Junk science that destroys an analog signal and is barely audible 15 miles away, unless you are a 50kw station. Look, I am an IBOC FM fan, but AM is garbage. I blame the INVENTOR of the damn system, not the engineer. It just does not work. It makes an already vulnerable station expose its achille's heel.

It is a shame the FCC refused to give any credence to Kahn's CAM-D. Now THAT's a digital system I'd be proud of putting on my stick. Not some overly expensive buzz maker that will destroy my coverage.

Tell me, why should a 1kw stick even look at IBOC? Or anybody less than a 10kw stick? It ain't worth it. It's garbage (even for the flame throwers).
 
So it is apparent that just installing an HD Radio signal generator is not enough for most AM stations to start broadcasting digitally (contrary to what I've read on various TX manufacturer's websites). It could easily include rebuilding the entire transmission path for a station and possibly even relocating to a new tower site.

None of this is cheap or easy. And given that so many AM stations are just breaking even or, at worst, going dark, makes it obvious that HD-AM is the wrong strategy for promoting the band's survival.

C5
 
Only stations that I've heard HD-AM sound decent on are single tower installations that had C-Quam AM Stereo running on them at one time, as that had "everything just right" for the C-Quam and that appears to make it easier to get HD-AM to work. However, when running C-Quam that had stereo out a long distance with skywave, HD doesn't go nearly as far, nor does it sound as good as a fine-tuned C-Quam system.

I pushed the FCC for better AM receiver/tuner standards as part of the FM-HD ruling, and would have allowed CAM-D, C-Quam, DRM, and others to present their systems WITH an improved AM tuner standard as well. Looks like it's too late? Maybe not, WLS sounds great in CQUAM at night at my location, as does KCJJ.
 
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