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Re: [IRCA] Skywave noise
> > But isn't IBOC AM only 1% also?
>
> This is an amazingly persistent myth. There are two possible settings
> for the digital power, according to the NRSC-5 specification. One
> sets the digital power to 5.8% of the analog (carrier) power, and the
> other sets it to 6.8% of the analog power.
It turns out that there are no real exact limits. The one AM station on
which I've seen the installation first hand has totally adjustable power for
the digital sidebands. This particular station had the power turned down a
bit at a time until the unwanted spurs fit below the -65db limit in the
mask. Instead of -25db from carrier that ended up about -32db. Even then
the spurs were right at the -65db limit.
FWIW, we tried running this into the night antenna system. It was so
distorted the Day Sequerra tuner in the transmitter room wouldn't decode at
all, nor would any other receiver we tried. So, it's not on at night and
probably won't be for years, if ever. That will put this station at a
disadvantage in the unlikely future of IBOC success.
This installation used a Nautel HD exciter, so perhaps other brands like
Harris or Broadcast Electronics have specific settings as mentioned.
I've also heard of another situation where the interference caused the IBOC
station to have to turn down it's sideband power by a fair amount - 6db I
think. Too bad that the 1040 station in upstate NY couldn't get that
cooperation from the FCC. It would please me no end to see WBZ-1030 forced
to drop the IBOC power. It's a bloody nuisance here, even causing noise on
WINS-1010 daytime. It also causes background hiss on the WBZ analog signal
on some radios including the one in my wife's 2004 Chrysler. So, WBZ has
lost an occasional listener in the southern MA area. Not that they care,
I'll bet. It's also noticeable on the audio in the EAS receiver at several
clients. That's not good at all. I'm also not looking forward to KDKA IBOC
interfering with WBZ on several EAS receivers. That is potentially
dangerous.
Craig Healy
Providence, RI
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