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At 12:56 AM 3/25/98 -0500, you wrote:
>As I was passing by the B.U. School of Public Communications today, I
>noticed a sign on the building reading "WTBU 640 AM 89.3 FM."

Those big brass letters threw me for a loop the first time I saw them as
well -- you'd think they were running a "real" station out of that building!

>Which makes me think that WTBU still transmits on carrier current.  But
>what's this 89.3 FM?  A low power transmitter?

Well of course there's always a transmitter; the question is what the
transmitter is feeding it's RF into and where & what the signal is being
radiated from.  I'm not close enough to anything going on at BU to know the
intimate details, but to my knowledge both the AM and FM WTBU systems come
under the generic heading of "carrier current".  The (I'm sure older) AM
system probably uses the conventional approach of a coupler atached to the
building's AC wiring, but I suspect the FM side of things uses one of the
newer "leaky" coaxial cable systems such as the type sold and installed by
LPB Inc. these days.  LPB may use a diffrent name for this type of system
but I've heard a lot of people still refer to it as "carrier current" as the
end result is more or less the same; the main diffrence is with the old
system you're dealing with the wiring already installed in the building for
another purpose while the new system uses wires installed for the sole
purpose of radiating a radio signal.