AM band question

["Bill O'Neill" <billo@erols.com>]

In relatively simple language, what is the principle by which AM
stations on the low end (higher meters) can have a larger footprint
than a high end counterpart with the same (or much greater) power?
And I also plead ignorance to which height AM towers are the most
efficient for coverage at a given frequency.  For instance, I'm
somewhat familiar with the installation for WCAP (980 Lowell) which
has 4 towers at 256' HAGL (2 sticks day, 3 night).  Is HAGL determined
by frequency and what other alternatives are there (and I assume the
pattern/phasing is notwithstanding)?

Is there 'Radio Engineering for Dummies' or something like that which
speaks to stuff like this in dull-normal ranges of intellectual
functioning format?

Bill O'Neill

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