Re: [IRCA] Another perspective on AM IBOC, from the broadcasters' mailing list

[Barry McLarnon <bdm@xxxxxxxxxx>]

On Tuesday 27 March 2007 11:25, Scott Fybush wrote:
> This caught my attention over on the [BC] mailing list, and I suspect it
>
> may stir up some discussion on the DX lists:
> > I have been investigating some of what has been said on this
> > list about IBOC on AM. It appears as though it is really a
> > receiver problem. Don't get me wrong. I'm not advocating
> > trashing 150 bazillion conventional AM radios so that IBOC
> > will work. Instead, as I am beginning to understand the
> > technology, if an AM radio was designed with more modern
> > technology, digital demodulation of AM with a wall filter,
> > there would be no buzz. There really is plenty of bandwith
> > available for IBOC on AM. The feds were not bamboozled.
> > The problem is that AM radios of conventional design,
> > superheterodyne with envelope detectors, cannot handle the
> > adjacent channel IBOC interference at reasonable cost.
 [remainder deleted]

The operative phrase in the above is "beginning to understand".  Sure, you can 
improve adjacent-channel selectivity by using digital techniques - nothing 
really new there.  The Blaupunkt Digiceiver comes to mind, and a Motorola 
chipset that was announced with much fanfare several years ago, and then 
seemed to sink without a trace.  This concept doesn't address the major 
problem, which is *co-channel* interference from the digital sideband of a 
1st adjacent channel IBOC signal.  This interference is, for all intents and 
purposes, broadband noise, and there is no practical way to get rid of it.

Even if there were a practical way to do it, so what?  A fundamental tenet 
behind the development of an acceptable IBOC system was that it had to be 
compatible with the existing installed base of analog receivers.  When it 
turned out that the laws of physics could not be repealed, the FCC chose to 
ignore that tenet.  Money talks, and the big players must get their digital 
service for the big markets.  Collateral damage?  Tough luck.

Barry

-- 
Barry McLarnon  VE3JF  Ottawa, ON
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