[BC] 750-kW Class IA AMs

[Dan Strassberg]

Scott Fybush wrote about Westinghouse's plan to move WBZ to Provincetown had
the FCC ever been put in place its proposal to allow approximately half of
the IA clears to run 750 kW.

It certainly would have been interesting. No doubt, WBZ's night signal would
have covered a lot more than those chimeric 38 states (and all the best
Canadian provinces). But the day signal in Boston and the immediate area,
though still the best in the market, would actually have taken a hit.
Currently, transmitting from Hull, WBZ, according to the V-Soft signal
stength by Zip code Web site, delivers almost 300 mV/m to Winthrop. Winthrop
is on a peninsula that juts into Mass Bay (or Boston Harbor) and is a
straight shot across salt water from WBZ's transmitter, which must be about
10 miles away. Believe it or not, the 750 kW directional signal, whose
inverse-distance field at 1 mile in the direction of Boston would have
exceeded 10V/m, would have been down to something like 150 mV/m 70 miles
away. That is, at the waterfront in Boston or Winthrop, the 15X power
increase coupled with the move of approximately 60 miles to the southeast
would have cut the signal in half. I don't know how WBZ's overall daytime
coverage would have fared. The signal on the outer Cape, which is currently
not that impressive, would have been so good that everyone with fillings in
his teeth could have listened without a radio--whether or not he wanted to
listen ;>) But inland in New England, I'm not sure how the coverage would
have compared. The greater distance from the transmitter might have, in
effect, cancelled out the power increase
.
On the other hand, in central New Jersey, where you can pick up WBZ now
during the daytime because so much of the path from Hull is over salt water,
WBZ might have become the strongest AM signal.

And then there would have been the problem of phasing from the skywave that
followed the great-circle route around the globe and came back to
Provincetown as a TA catch ;>) How many hops would THAT take? Remember that
the effect of the DA would have been to effectively double the
signal-strength in front of the pattern, producing the equivalent of 3
million watts (from half-wave towers) in front of the pattern. Are there any
superpower MW stations, in, say, the Middle East or Russia that run as much
as 3 million watts? If so, how do they do in, say, southern Spain or
Portugal during daylight hours?

--
Dan Strassberg, dan.strassberg at att.net
eFax 707-215-6367