WEEI tower heights

[Dan.Strassberg]

A few weeks ago there was a thread here about the WEEI tower heights.
I remarked that the heights in the CDBS records for WEEI are not the
correct physical heights and include a comment that the electrical
heights shown (207 degrees for each of the three towers) include the
effects of mutual inductance among the towers and a propagation
velocity within the towers that is less than the speed of light in
free space. These effects increase the effective electrical height and
make the towers behave as if all three were pretty much the same
physical height. I noted that Entercom had filed an application to
correct the pattern augmentations to make the patterns agree with
measurements made since a short communications tower was constructed
on the property. After a year, the FCC has finally granted Entercom's
application, which makes no physical changes in anything.

I reread the application today and, alas, although the text kind of
explains what's going on, the "corrected" CDBS records, if anything,
are even more confusing than the old ones. Part of the problem appears
to relate to the ground system, which is elevated 7.5' above ground
for the first 30' from the base of each tower. Apparently the
engineers who designed and built the array back in 1947 calculated
heights above ground from this elevated reference and the just-granted
application continues this bizarre practice. Moreover, the new tabular
data appears to confuse electrical height with physical height and may
confuse distances in electrical degrees with distances in meters. The
reason for that, I suspect, is that 1 electrical degree is very nearly
(though not exactly) 1 meter at 850 kHz. (1 degree = 0.979m @0.85
MHz.)

One thing is certain, the towers are of unequal physical height, as
you will notice if you look closely. The tower heights appear to be
(from west to east) 640', 600', and 560' above the tops of the base
insulators, though I would not want to stake even the price of a cup
of coffee on those last numbers.

-----
Dan Strassberg (dan.strassberg@att.net)
eFax 1-707-215-6367