Eextensive and careful research into ground systems in the 1920s and 1930s
resulted in the FCC "standard" ground system for AM radio stations of 120
buried radials, each 1/4 wavelength long -- or in the case of clear channel
stations with 5/8 wave towers, a combination of 1/4 wave and longer (1/2 to 5/8
wave) radials.
Prior to the implementation of these standard ground systems, quite a few AM
stations used rooftop installations on downtown hotels or office buildings.
When I was in broadcasting, I heard quite a few stories from the old-timers
that the new ground-mounted installations never provided as good a coverage as
the old rooftop systems. Of course, some of these claims are due to the fact
that the new systems were located away from the center of town, but many
stations did not move very far.
So it's probably safe to say that some of those rooftop installations DID work
better than their ground-mounted replacements. I hope the ongoing study of
elevated radials helps us figure out how they work, and under what conditions
they work best.
(Just an editorial comment to encourage more serious effort in this area!)
73, Gary Breed, K9AY
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