[BC] DA Bandwidth

[Stan Tacker]

Barry,

Good analogy and good point.  The First Report and Order was issued without
the benefit of the experience that we have to date with real world iBiquity
IBOC performance.  Many issues were left open, the most significant of which
was AM nighttime operation.  

I have to disagree with those who say the war was over with the issuance of
the First R&O.  Some of the underpinnings of that Order have been proven not
to be true.

For instance, the Order justifies the interference/benefit trade off by
concluding that the digital hybrid AM signal is "more robust" than analog
AM.  One engineer for a group with many AM IBOC operations has stated that
the iBiquity digital system is subject to loosing its lock in the presence
of impulse and broadband noise (hmm, that would include lightening and
powerline noise).  On the analog side, the hybrid system is, if anything,
more fragile than non-iboc AM.  A major cause of daytime fading of an AM
system is due to re-radiated sidebands receiving the receiver out of phase.
(the reradiation can be attributed to powerlines, metal buildings,
overpasses, etc.)  Once the sidebands cancel each other, the digital hiss
rushes up to fill the void.  The hybrid signal carries significant
"self-interference" potential.

The First R&O also justified the interference/benefit tradeoff by providing
that the conversion to the ibiquity system is voluntary.  It also provided
that interference would be handled on a case-by-case basis.

The fat lady hasn't sung yet.  Even if the Final Order ratifies the First
Order, there will be significant uncertainty if the Commission maintains its
case-by-case interference resolution policy.  

Why invest in the technology if your use of it could be later limited?

-----Original Message-----
From: broadcast-bounces at radiolists.net
[mailto:broadcast-bounces at radiolists.net] On Behalf Of Barry McLarnon
Sent: Friday, June 02, 2006 2:07 PM
To: Broadcasters' Mailing List
Subject: Re: [BC] DA Bandwidth

On Friday 02 June 2006 00:53, Phil Alexander wrote:
> > I agree that it's a good service, so it's sad to see it
> > being trashed. How do you propose to keep those small
> > and medium stations alive?
>
> By devising a process whereby we may determining the possible
> problems of VSWR and pattern b/w before equipment expenditure.
>
> By a rational approach to pattern b/w regularization using
> existing equipment modification where possible.
>
> By technical conflict/interference mitigation avoiding
> litigation.

As I've said before (ad nauseum, no doubt), bringing DAs into spec over the 
30 kHz IBAC bandwidth doesn't solve the problem, it just keeps it from 
getting even worse... and, of course, provides lots of business for the 
consultants.

> Finally, by a liberal application of common sense.

Good, you see it my way. :-)  Common sense dictates shelving an unworkable 
scheme in favor of something better.

> IOW typical problem SOLVING measures.
>
> My opinion of IBOC is low for many of the same reasons
> you are opposed, but also for the way in which the RM's
> and our FCC have been manipulated, but what's the point
> in crying over spilt milk? This was over except for the
> shouting FIVE years ago.
>
> Could it have been done much better? DRM shows us the
> possibility. Will DRM be given the nod at this late date?
> Given the present political climate and the money at
> stake, I think not. That doesn't mean I like it, but that
> is reality. The time for strong opposition and alternatives
> was six years ago. The case has been closed for five. We
> lost that battle. The problem we confront is saving what
> we can for the next time. Or, we can do nothing and lose
> everything at the end of the day.

Sorry Phil, but I'm not buying it.  Five/six years ago, nobody (with the 
exception of a few insiders) reallly knew about the true nature of this 
system.  Thanks to a lot of hype and a carefully crafted evaluation of the 
technology, a lot of folks were misled.  What's been happening in the past 
few years is essentially a field trial, albeit a limited one (less than 3% 
of AM stations participating) that avoids worst case conditions (night 
operation).  Even under those limited conditions, it has become evident to 
many observers that there are severe fundamental problems in the system 
design.  Use of this system is not mandated, and this is not an 
irreversible process.  When rational people discover that they've embarked 
on the wrong course, they don't plow recklessly ahead, they stop and look 
for better alternatives.

IBOC is like a drug that got conditional approval from the FDA on the basis 
of data submitted by the manufacturer.  Subsequent clinical trials with 
unbiased observers, however, have shown that the drug has severe side 
effects, including many probable fatalities, that the manufacturer had 
assured us would be inconsequential.  Turns out that the cure is much 
worse than the disease.  The obvious next step should be to pull the drug 
off the market.  Unfortunately, a few folks have already become addicted 
to the drug, but they'll get over it, and eventually find something better 
that doesn't have the vicious side effects (like the buzzing it causes in 
your ears).

The bitter pill called AM IBOC may be harder to get rid of, since the "FDA" 
in this case won't listen to reason, but it's still worth the effort.

Barry

-- 
Barry McLarnon VE3JF  Ottawa, ON


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