[BC] Why superpower? (was: WLW my take)

[Dan Strassberg]

It was stated that WWJ's pattern maximum (7981 mV/m @ 1 km by night) is
equvalent to approximately 300 kW. The equivalent power is, in fact, almost
50% higher! If you use the pattern RMS--2665 mV/m @ 1 km--you find that the
field-strength ratio is 2.99. Hence, the power ratio is 2.99^2 or 8.94,
which makes the equivalent power something like 448 kW at the pattern
maximum. If you use the corresponding figures from the (five-tower) day
pattern, you still get an equivalent power of almost 390 kW--almost 30% more
than the claimed 300 kW.

Somewhat curiously, 2665 mV/m from 50 kW works out to 376.9 mV/m/kW, which
is slightly more than the Class A minimum of 362.2 mV/m/kW @ 1 km, yet only
two of the six towers in WWJ's night array are tall enough (168 degrees)
that, operating individually, they could produce a nondirectional field of
362.2 mV/m/kW @ 1 km. The other four towers are 138 degrees. The two tallest
towers are, I believe the highest-power towers in the array, so that
partially explains the seemingly impossible efficiency. My guess is that
most of the rest of the rest of the explanation lies in pattern
augmentations and in the fact that the unaugmented standard-pattern RMS is
1.05 times the theoretical RMS.

However, WWJ is a Class B. If you took the MINIMUM efficiency for a Class B
(281.7 mV/m/kW @ 1 km), you would get a pattern RMS of only 1992 mV/m at 50
kW. 7981/1992=4. By that measure, the equivalent power of WWJ's night
pattern at the pattern maximum is 800 kW! Since WLW was a Class IA and is a
Class A and WWJ, despite its Class B status, has slightly more than Class A
minimum efficiency at night, the comparison to WWJ's pattern RMS is probably
more meaningful, but even using that measure, 300 kW understates by almost
1/3 the equivalent power of WWJ's signal at the night-pattern maximum.

Note that not far from WWJ's new array is the new nine-tower array of WXYT.
As you might expect from the larger number of towers, WXYT's array produces
an even higher ratio of maximum to RMS fields. WXYT's maximum value at night
is 7752 mV/m @ 1 km--not even 3% less than WWJ's night maximum, but the RMS
is 2241 mV/m @ 1 km--16% lower than WWJ's night pattern RMS. WXYT's towers
are only 82 degrees high, but you could say that WXYT's equivalent power at
the night-pattern maximum is almost 600 kW based on the pattern RMS.

Of course, to be completely fair, WLW, for at least part of the time it ran
500 kW used a three-tower DA at night to protect CBL Toronto (then on 690).
The field toward Toronto at night was limited to the equivalent of 50 kW ND.
I have never seen a polar plot of WLW's 500-kW night pattern, but I guess
that we must assume that the field around an arc of at least 180 degrees
centered on the southwest must have exceeded 3.16*2700 mV/m @ 1 km by 25% or
more.

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