[BC] Documented harmful interference

[Phil Alexander]

On 19 Jan 2006 at 19:29, DANA PUOPOLO wrote:

> I don't think they could win. Both stations are operating well within FCC
> requirements/tolerances.
> 
> Another story....
> 
> Today I was in Worcester. WILD's main channel barely comes in there, but their
> IBOC on 1080 was strong enough to put hash under WTIC 1080 from Hartford, a
> class A station running 50kW Non-D. Worcester is a city of about 100,000 well
> within WTIC's daytime coverage contour (perhaps 55 miles away as the crow
> flies). The hash was there all the time and was about 10-12 db down from the
> WTIC audio. It made WTIC quite tiring to listen to.
> 
> How come an analog AM station has to protect the WTIC .10 mV/m contour, while
> and IBOC carrier can DUMP all over it?
> 
> Anyone??

*IF* WTIC wants to make an issue of it, WILD probably would reduce their
digital level a few dB, either voluntarily or involuntarily. It is clear
WTIC is entitled to protection in its primary service area. 

However, according to 73.21(a)(1) while, "Its primary service area is 
protected from objectionable interference from other stations on the same 
and adjacent channels," "its secondary service area is protected from 
interference from other stations on the same channel." IOW, the primary
coverage gets co-channel and adjacent channel protection while the
secondary area gets co-channel protection only. By FCC definition
WILD is adjacent channel interference. The fact that WILD *emits*
directly in WTIC's channel is not recognized by that definition.

73.182(d) further defines, "The groundwave signal strength required to 
render primary service is 2 mV/m for communities with populations of 2,500 
or more and 0.5 mV/m for communities with populations of less than 2,500.

Thus, it appears WTIC would have to show objectional interference as
defined by relative signal strengths within their 0.5 mV/m contour in
a town having a population of less than 2,500, or within their 2.0
contour in one more than 2,500. Based on such a showing, the FCC might
grant relief, or depending on the next report and order, a higher
threshold may be set. Realistically, they will probably have to show
that WILD exceeds the NRSC-5 mask within their primary service area
before anything is done about it.

OTOH, I expect a Class B might have to show the same within their COL
or region adjacent to it, IOW have a geographic threshold added to
the contour threshold of the Class A standard. This is pure conjecture
on my part, as the rules give both the same protections, but reading
Doc. 99-325 makes me think the evaluations of interference will lean 
in that direction in the next report and order.

The operative philosophy seems to be that some interference is a price
ownership is prepared to pay to move toward a digital system that
ultimately promises less interference and better audio than the system,
IOW transmitters + typical receivers offers today.

That is HOW they do it. Right or wrong does not appear to enter the
picture. It is a business decision trading interference during the
interim hybrid period for better service in the long run.


Phil Alexander, CSRE, AMD
Broadcast Engineering Services and Technology 
(a Div. of Advanced Parts Corporation) 
Ph. (317) 335-2065   FAX (317) 335-9037





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