WMBR and stereo (was Re: WHIL/WWEL)

[Shawn Mamros <mamros@MIT.EDU>]

Rob wrote:
>On Mon, 23 Nov 1998, Shawn Mamros wrote:
>> I could tell a lot of stories about that (expletive deleted) Cetec, none
>> of them good ones.  Fortunately, we ditched it in favor of a Broadcast
>> Electronics exciter/transmitter around 1990 that's proven far more reliable
>> (aside from the occasional blown fuse caused by a lousy electrical supply).
>
>As I recall this was when WMBR went stereo. I always thought it ironic
>that one of the last Boston FM's to go stereo should be MIT's.

Ironic indeed...  Actually, stereo came to WMBR a few years earlier, in
1987.  (And I got to flip the switch! :-)  The transmitter room had actually
been stereo-capable since 1979 - an Optimod 8000A stereo generator had
been purchased around the same time as the Cetec.  Problem was, the studios
were still using the early 60's vintage broadcast consoles and Master Control,
which were only wired for mono.  It wasn't until the mid-to-late 80's that
we could finally afford to replace the consoles and rewire/rebuild Master
Control for stereo - and it wouldn't have been possible without our
fundraising drives, which had become a regular annual event only a couple
years earlier.  As with many things in radio, it was solely a matter of
money (or lack of same...).

I keep wondering whether the MIT students that first built the Walker
Memorial studios, including the broadcast consoles, knew that FM stereo
would soon be coming into being or not.  After all, the FCC authorized
FM stereo in the same year that WTBS-FM signed on, and WCRB at least was
using it by the end of the year.  The consoles had two mono channels and
a cue channel - in theory, at least, one could've combined both mono
channels into a stereo channel.  For a while after we went stereo, we
actually did try to use one of the old boards on an occasional basis.
Doing a stereo show was possible, but extremely awkward, and most people
of course preferred the brand-new board with the built-in stereo faders.

There's actually a story to tell about the conversion to stereo that possibly
only techies can relate to...  Up until the switch to stereo, the Optimod had
been in the airchain for many years, used solely as a limiter.  A few days
before we had scheduled "the big switch", after we had completed all the
necessary connections, we finally got around to testing it all out - late
at night, after the regular programming signed off.  We signed back on
with the standard spiel about "conducting testing", then flipped the stereo
switch on the Optimod.  The stereo light on the receiver came on - and with
it a quite audible and annoying high-frequency tone.  Flipped back to mono
- - tone went away.  It took literally all night to figure out the problem,
and it wasn't until we had figured out that the tone was out of phase that
it dawned on us - there was a faulty capacitor in the Optimod that created
an oscillation in the 25-to-32 kHz range.  Inaudible in the L+R audio (which
only goes up to 15 kHz in FM), undetectable in mono mode without a spectrum
analyzer (which we didn't have) or somesuch, yet loud and clear once we
turned the stereo pilot on, since it was smack dab in the middle of the
L-R signal!  Definitely one of those experiences one can now look back and
laugh at, but it was sure frustrating that night...

- -Shawn Mamros
E-mail to: mamros@mit.edu

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