[BC] AM and FM HD Radio

[Phil Alexander]

On 18 Jan 2006 at 10:59, Rich Wood wrote:

 
> The objection, as I see it, is that never in radio's history has a 
> system been approved that harmed its neighbors. We can argue till 
> doomsday about FM stereo systems. A bad one hurts only the user. It's 
> his or her choice. This technology allows someone else to determine my fate.

Just curious. What would you call the breakup of the clear channels?

> >The problem as I see it is that the HD signal does not carry as far 
> >as I thought it would.  Is that an issue with the receivers?  Or is 
> >it an issue with the low power of HD signal?  Audio wise I am 
> >impressed with the HD signal even when stations run HD2.
> 
> As I understand it digital power levels affect the level of 
> interference. During my two months with a receiver it seemed to me 
> that levels were all over the place.. Some digital signals equaled 
> the analog. Most didn't. That caused additional, annoying problems of 
> mode switching on top of multipath. My problem here isn't multipath. 
> It's the occasional disappearance of the signal. Digital isn't fixing 
> that.

The problem is IBOC. So long as the digital signal must occupy part of
the adjacent channel the digital signal level must be extremely low
with an average power around 20 dB below the analog carrier. All 
indications are that the level can be increased at least 10 dB without
interference problems if the analog signal is removed and the digital
signals are folded into the cleared spectrum.

Fundamentally, the purpose of IBOC is to sell enough receivers to
permit this without inconvenience to the majority of the audience.

> I'm resigned to the fact that radio will never again be considered an 
> audiophile medium. 

It never really was except for the few years we called the '50's and
very early '60's. Once stereo began, true high fidelity went away if
it ever was present. To me, REAL high fidelity is me sitting on the 
lawn outside the shed at Tanglewood with a good bottle, cheese 
optional.

As soon as you put a mike in the circuit, distortion of the original
performance intervenes, and then you add an amplifier and speakers,
that compounds it beyond measure. I've never heard a recording of
a symphony that came close to the feeling and nuance of the real 
thing.

> It doesn't have to be. it just has to be non-fatiguing if we expect 
> people to stay for long periods. 

At least that capability is inherent in the digital medium. What is
being done with it (on CD's for example) is another matter.

> I propose that we dump that tired old "think out of the box" and 
> replace it with "think out of your bandwidth."

But that means you are IN someone else's bandwidth, doesn't it?
How like the real world where we call that IBUX. <g>


Phil Alexander, CSRE, AMD
Broadcast Engineering Services and Technology 
(a Div. of Advanced Parts Corporation) 
Ph. (317) 335-2065   FAX (317) 335-9037





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