Re: [IRCA] DRM vs IBOC

[Scott Fybush <scott@xxxxxxxxxx>]

Patrick Martin wrote:

> You are so right. KGO 810 running 50 KW U3 had that issue. When they are
> using IBOC at night, it was impossible to get rid of that hash right on
> 810.00 KHZ. No matter what I do. It is horrible to listen to. I had it
> on the R8, SPR4, and even the Super Radio.  I contacted an engineer at
> KGO about it and he told me that they were trying to get rid of it. But
> the last time I heard KGO on with IBOC several weeks back they still had
> that hiss on channel. I don't know during the day in the KGO area if it
> still an issue as KGO's signal up here days is not strong enough for
> 100% quieting as they are most nights. If this is going to be an issue
> with directional AM IBOCers, then people will tune out and complain. 

Seems to me we've had this discussion before...this is likely to turn 
out to be largely an issue of the skywave propagation wreaking havoc on 
the phasing of the signal when it reaches you. The groundwave signal, 
without that phase distortion, should exhibit much better symmetry of 
the digital carriers, which should cancel themselves out on an analog 
receiver.

Here's where it gets interesting: if WBAP stays strictly analog, and 
assuming KUTR doesn't throw much signal your way at night, I'm guessing 
there won't be any 820 stations throwing low-side digital hash onto 810 
where you are. 800, being a Canadian/Mexican clear, won't have anyone 
pumping out high-power digital at night either. So 810, at least out 
west, may be one of the few clean channels where on-channel 
self-interference from the IBOC carriers turns out to be an issue.

Most of the other clears that still have a wide reach at night are 
likely to end up suffering from enough adjacent-channel hash that any 
on-channel phase-distortion hash is a relatively minor concern by 
comparison, for whatever skywave listeners there might be.

It's important to remember that we're still in the very early 
experimental stages with all this. As I said the last time this came up, 
broadcasters are still learning how to tweak directional arrays to 
minimize some of these issues as they come up. There may be solutions 
that they haven't thought of yet...or there may simply be some stations 
where it ends up not working. (Up in your neighborhood, Patrick, there's 
at least one DA I know of - KOAC 550 - that simply cannot pass IBOC 
because of the way it's designed. There are surely more of those to come.)

No, it's not going to be pretty, especially at first...but if nothing 
else, I'm at least very curious to hear what really happens when the 
rubber hits the road, as it were. This is new enough to everyone 
involved that I'm not making any predictions yet about how it will all 
play out. It's certainly far from over.

s
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