AM Radio coverage

Dan Strassberg
Wed Feb 28 17:09:23 EST 2007

You can slice it any way you like, but KFI never could legitimately have
been described as the most powerful AM station in the US. Because it
operates on 640 kHz, however, KFI is the lowest-frequency Class A (ex-Class
IA) AM in the US, although Canada and Mexico have such stations on 540.
Since KFI runs 50 kW-U ND-U from an approximately half-wave tower (or it did
before a private plane toppled the tower a couple of years ago), if you rank
it on the basis of antenna efficiency, it is slightly below the middle of
the pack of Class A stations. Since the plane crash, KFI has been operating
at reduced power from a very short and inefficient tower. After long and
bitter negotiations with the FAA, private pilots, and NIMBY neighbors, KFI
recertly announced plans to replace the fallen tower with a slightly shorter
but much more massive top-loaded structure of equal electrical efficiency.
Those plans have yet to be approved by some of the parties who must sign
off, however. If you compare KFI with directional 50-kW stations (mostly
Class Bs), some of which have very high-gain antennas that produce
phenomanally high effective power over a very narrow arc (albeit with RMS
field strength over 360 degrees usually considerably lower than KFI's), KFI
is not even in the same league. Amomg US stations, honors for highest field
strength go to WWJ Detroit (effectively 800 kW--depending on how you figure
it). Among nondirectional 50-kW stations in the US, the honors probably go
to KDKA, which uses a segmented radiator of unconventional design to achieve
higher efficiency than is possible with either a conventional radiator or a
top-loaded radiator. KFBK Sacramento uses two segemented Franklin radiators
in a directional array. KSTP St Paul uses a segmented radiator for its
nondirectional daytime operation but uses conventional half-wave towers for
its directional operation at night.

Dan Strassberg,
eFax 707-215-6367

----- Original Message -----
From: "Russ Butler" <>
To: <>; "Russ Butler"
Sent: Wednesday, February 28, 2007 4:05 PM
Subject: AM Radio coverage

> Speaking of AM radio station coverage on this list recently, I remember
> that it wasn't unusual for WBZ's Norm Nathan's late-night telephone
> conversations to include a caller from London or other countries "across
> the pond" with their Hull, MA salt water-grounded transmitter site.
> Also, I found this comment online from John Rook (dot) com, a former
> Program Director at KFI in Los Angeles:
> /
> KFI, at 640 on AM dial in Los Angeles is known as the nation’s most
> powerful radio station. Listeners from Hawaii to New York and Canada to
> Mexico for years tuned in to hear Dodger games exclusively on the
> station. The premium facility had been sold to Cox Communications of
> Atlanta for a record breaking $15 million cash in 1973, then the highest
> price ever paid for a radio station./

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