Re: [IRCA] Re; 1130 Interference

[Scott Fybush <scott@xxxxxxxxxx>]

Patrick Martin wrote:

> I can believe that as most people don't have a clue why there is
> interference. All they know, is they don't like it. CKWX is a very
> popular News station covering the Lower Mainland and Vancouver Island,
> so I am sure the complaints are everywhere.

Doubtful. The reason the issues are cropping up in the Fraser Valley has 
to do with poor ground conductivity between the CKWX transmitter site 
(south of Vancouver in the Richmond/Surrey area) and the relatively 
distant Fraser Valley. Within most of the rest of metro Vancouver, CKWX 
puts a strong enough signal to overcome any incoming interference from 
KPWX. But out in the Fraser Valley, CKWX barely puts a 0.5 mV/m signal, 
which is fairly weak - and thus subject to interference from KPWX.

> But if this goes on too long, I am sure CKWX will lose listeners. People
> love the All News stations and depend on them at rush hour and that is
> when the QRM is apparent.

They may or may not see any real-world ratings hit; it depends on how 
much of the ratings panel is out in the areas east of Vancouver 
suffering the interference.

> It will be interesting to see how this plays out. Here on the Oregon
> Coast I am far enough away from Mt. Angel to notice any power change.
> They probably should have had the 6.5 KW during Critical Hours. 

If they'd been protecting a US station on 1130, they'd probably have had 
even lower critical-hours power, since US class A and B stations (unlike 
Canadian stations) are protected from incoming skywave interference 
during critical hours.

And it's important to understand where that "6.5 kW" figure comes from. 
It's really 6250 watts, and there's nothing magical about it - it's 
simply that the FCC allows directional AM stations to run a maximum of 
25% of their daytime power under STA, and 6250 watts is 25% of 25 kW. 
(Similarly, WWVA will be running 12.5 kW at night under STA once it 
completes rebuilding the first of its three downed towers later this 
week; that's 25% of its licensed directional 50 kW.)

In KPWX's case, the STA operation was only for a few weeks, to allow 
KPWX to make the ground conductivity measurements it needed to make as 
part of the 50 kW application process.

s
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