[BC] Digital coverage

[Phil Alexander]

On 26 Dec 2005 at 13:36, Scott Fybush wrote:

> Hasn't this been an issue with at least one of the Grand Rapids superpower Bs?

I haven't followed that, but unless spacings were increased, problems
are predictable. However, it is a small part of the spectrum in a small
part of the country, not a generalized problem like the G-F/SS Class A's.

> I seem to recall that one of them - WBCT 93.7? - was running its IBOC 
> subcarriers substantially below the standard injection level to 
> reduce interference to one of the nearby adjacent-channel stations.

A reduction in the 6 to 8 dB range would put them more or less in line
with the standard Class B's.

> Without protection beyond standard class B contours, neither of those 
> huge West Michigan signals (WBCT is 320 kW, WOOD-FM is 265 kW) seems 
> to enjoy much in the way of added coverage these days. Too much 
> nearby stuff on the dial. WOOD-FM, at 105.7, is even getting a 
> second-adjacent move-in within its own market soon!

Most of today's tuners fall far short of the performance of a 1960
vintage tube type Fisher or Sherwood. Those were spec'ed for 20 dB
quieting with 0.5 - 0.7 uV/m signal and they did it. Give those a
20 uV/m signal and they sounded fantastic. I was involved with one
of the early OTA FM relay networks back in those days, and noise
was not a big problem with a good antenna and what amounted to almost
an over the horizon signal. Of course those receivers cost $150-200
in 1960 dollars which would translate into well over $1,000 today.
But, they did work - did they ever.

Remember that the early coverage contours were the 60 dBu (1 mv/m)
and the 34 dBu (50 uv/m). The addition of the 70 dBu came later.
Even the cheapest early FM radios gave fine performance on a 60 dBu
"local" signal.


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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