Hip Deep in the Big Muddy of HD Radio

A correspondent sent this link along about the latest developments in HD radio, along with a scathing commentary about what this latest insanity portends:

From http://www.radio-info.com/newsletter/html/tri-11302011.html this morning (11/30):

HD RadioImproving HD Radio reception is the goal of an FCC Public Notice on “Asymmetric sideband operations”, and now we’ve got the comment dates. Comments are due by December 19, with reply comments due January 3. This is the story TRI told you about on November 2 – “’Asymmetric’ may not sound sexy, but it might be one key to improving coverage for HD Radio FMs.’ Basically, the Commission says “a significant number of FM stations are precluded from taking advantage of the full 10 dB digital power increase permitted by the order, due to the presence of a nearby station on one but not both of the first first-adjacent channels.” If stations could run an “asymmetrical” signal – stronger on one side – they could raise digital power.

So the Federal Cookie Company is moving ahead with this idiotic idea.  It won’t improve “HD” coverage significantly, but it will increase interference to adjacents, at least on one side of the analog channel.

The “HD” signals are not sidebands in the literal sense of the word. They are two independently generated digital signals, one occupying the closer half of each first-adjacent channel.  And they are not synchronized.  That accounts for both for the excessive time delay imposed on the analog signal, which is necessary to keep it synchronized with the digital output at the receiver, and for the “HD” system’s relative (not absolute) advantage in the face of multiplex under some (not all) conditions.  (The two “HD” signals seldom suffer identical interference, and an “HD” receiver delays the two side-channel signal, picking and choosing whichever parts of each signal seem most intact to reconstruct an undamaged digital stream.)

Of course, that won’t work if one of the two digital side-channel signals is too weak to use!

So where could this increase the coverage range for “HD” FM?  Only on fixed (not mobile) receivers with (presumably) outdoor antennas.  Indoor antennaswould be subject to the effects of people — or pets? — getting too close and interferreing with marginal signals.  So who has that?  How about translators?

I can see no practical purpose (and I use the word “practical” loosely!) for asymmetrical “HD” except to enlarge the area where a network of analog translators could be used to make it possible for a signal from an HD-2 or HD-3 subchannel to reach a real audience.


3 Responses

  1. […] Hip Deep in the Big Muddy of HD Radio (keeppublicradiopublic.com) […]

  2. “HD Radio’s Dirty Little Secret”

    “We were told back in the beginning that the HD coverage would be equal to the analog signal. Unfortunately, the industry is now finding out this is not the case, that the HD coverage is considerably less, something like 60% of the analog coverage. We’ve also found that even in a strong HD signal area, a dipole antenna is required. We were also told that the HD would lessen interference with adjacent channel signals. That also appears not to be the case.”


    Perhaps, Dr. Conrad was at the BIG announcement! Calling all disgruntled HD Radio broadcasters – Keefe Bartels wants to hear from you! LMFAO!

  3. “IBOC Digital AM and FM Technology Launch”

    2002 – “In terms of coverage, the answer is it replicates the existing analog coverage, and that is all it can do. Not technically, but because of a regulatory reason. We could easily boost the IBOC power, but guess what, then that steps on the station next door… What the NRSC did say though, and we think this was a great vote of confidence, is, rather than bog down the process and wait for those nighttime results, we know we love it in the daytime, we know it represents, I think their words, a revitalization of the AM band… Bob Struble.”


    This is an article from iBiquity archives on the Wayback Machine from 2002. These are direct quotes from Struble at the NAB news conference, announcing HD Radio/IBOC. Obviously, Struble knew back then the problems with HD Radio, but the FM-HD power increase up to -10db was approved, anyway by the FCC. Struble lied about the coverage of IBOC, too. Notice how Struble blows off nightime AM-HD testing.

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