Re: [IRCA] DRM vs IBOC

[Barry McLarnon <bdm@xxxxxxxxxx>]

On Saturday 24 March 2007 21:17, Scott Fybush wrote:
> Until and unless we get to an all-digital world on MW and SW - and I
> don't see that happening for a very long time - that sort of
> digital-into-analog interference is going to be a reality, and DRM isn't
> a complete solution. Imagine two scenarios:
>
> 1. I'm a Canadian station on 740 running analog-only. You're a
> high-power US station on 750 running IBOC.
>
> 2. I'm a small station somewhere in Europe on 1296 running analog-only.
> You're a high-power station somewhere else in Europe on 1296 running DRM.
>
> It seems to me the ultimate effect is the same: the digital hash is
> going to contribute at least some additional noise to reception of the
> analog signal that occupies the same spectrum. The difference between
> the two scenarios is ultimately purely regulatory: in Europe, presumably
> some effort has been made to coordinate interference between two
> stations that are licensed on the same channel, whereas in North
> America, the licensing scheme never envisioned the guy on 750 spreading
> that much RF energy down onto 740's slice of spectrum.

Yes, this difference is at the heart of the problem.  The ITU has established 
protection rules for DRM operation that apply worldwide, except in Region 2 
(the Americas).  If a broadcaster wants to run DRM at a given site, then they 
must start with the analog protection requirements, and then adapt them for 
digital operation by reducing the digital power so that it is at least 7 dB 
below the analog (carrier) power that would be permissible from that 
location.  This recognizes that a digital signal causes more serious 
interference than an analog signal having the same power, which should come 
as no surprise to anyone who's listened to DRM signals or IBOC sidebands with 
analog receivers.

This is the crux of my submissions (futile, but satisfying) to the FCC: there 
is only one way to create a workable hybrid analog/digital broadcasting 
scheme in the AM band, and that is to coordinate the digital emissions as 
distinct entities, with proper protection to other stations, as for DRM.  If 
you simply let any station run digital signals on its adjacent channels with 
no regard to protection of other stations, you have a recipe for chaos.
We're about to get a glimpse of that chaos!

> That's ultimately an issue that will have to be resolved politically,
> not technologically. (Isn't that how so much of this story has gone
> already?)

Yes, indeed... politically, and probably in the courts.

Barry (who still holds out some hope that Canada will take a strong stance 
against this crud)

-- 
Barry McLarnon  VE3JF  Ottawa, ON
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