Technology Corner: Randy Hoffner
Remembering the World Trade Center
Reading the recent World Trade Center remembrances
from my colleague on these pages, Peter Prunty, brought to mind
my own memories of One World Trade Center – the North Tower.
Many who have worked in television in New York have spent time at
the Trade Center and your writer is one of those, having been involved
in early experimentation with –and implementation of –
the BTSC TV multichannel sound system at the flagship station of
another network (hint: feathers).
That station went on the air from the World Trade
Center in the latter half of 1983, the last station to make the
move from the Empire State Building. The move happily coincided
with the desire to experiment with that new technology: BTSC multichannel
television sound.
The station's Empire State Building transmitters
were too old to optimally broadcast multichannnel sound. Its incidental
carrier phase modulation (ICPM) specification – a parameter
that was little known or regarded before the TV multichannel sound
era dawned – was too high.
The World Trade Center installation featured two brand-new
pairs of RCA G-line low-band VHF transmitters and – although
there was, as yet, no interface for wideband BTSC signals on their
exciters – the transmitters were ready for BTSC with respect
to performance parameters.
There was some ongoing dispute with RCA over warranties,
so your writer was not permitted to so much as drill a hole in a
chassis, let alone add a wideband input to one of the G-line aural
exciters to add multichannel signals to the aural carrier. We were,
however, permitted to plug an FM radio exciter that we had on-hand
into the transmitters.
FREQUENT EXERCISING
The FM broadcast band is 88-108 MHz; the aural IF
frequency of the transmitter was 41.25 MHz. The exercise of adapting
the exciter to run at about half its lowest design frequency was
a real challenge. A custom crystal had to be ground, of course,
but a number of other components had to be changed as well.
It was relatively easy to persuade the frequency-modulated
oscillator to idle at the 41.25 MHz center frequency with a few
component changes, but the crystal-reference oscillator absolutely
refused to run with the custom crystal!
The solution was to tack in another – very simple
– crystal oscillator built around a single transistor. This
worked nicely. The exciter's modified output filter –
with its complement of capacitor/resistor network – was a mess
to gaze upon when its modifications were complete, but it made the
signal legal!
In addition to the FM exciter, an FM stereo encoder
was modified – the crystal in its 19 kHz oscillator was replaced
with a function generator that was locked to horizontal sync. This
made the encoder generate a pilot and stereo subcarrier at the appropriate
frequencies. The encoder was of the "switching" type,
which afforded no direct access to the L+R and L-R sum and difference
signals themselves.
The BTSC system required the difference signal to
be doubled in amplitude for transmission to improve its signal-to-noise
ratio. Further, the difference signal had to pass through a rather
sophisticated, sharp cutoff filter to protect the pilot. In order
to preserve stereo separation, the sum signal had to be passed through
an identical filter.
All this conditioning was applied using an external
box that matrixed left and right channel signals into sum and difference
signals, doubled the amplitude of the difference signal, passed
the signals through a pair of appropriate filters, de-matrixed the
result into left and right channels again and, finally, passed them
along to the stereo encoder itself.
A second audio program (SAP) encoder was made from
a modified FM subcarrier generator whose reference oscillator was
also locked to horizontal sync using a function generator; a professional
channel generator was made from yet another FM subcarrier generator.
Amazingly enough, all this homemade stuff worked (can you imagine
that in the digital age?) and the stereo separation that was achieved
was really quite respectable.
WAIT YOUR TURN
A request for special temporary authority to test
this TV stereo system on the air was made in 1983 – before
the BTSC system was officially approved – but the FCC required
us to wait until its rulemaking was issued. When this happened in
early 1984, we were ready to begin on-air experimentation.
Commercial BTSC encoders were not available until
early 1985 – the homemade system was used to generate all the
transmitted audio signals of a major television station in the country's
biggest market for a period of about one year. It only took a few
months for your author to stop waking up in the middle of the night
in a cold sweat, worrying about failures!
In addition to ongoing experimentation, it was used
to broadcast the first real commercial program with BTSC stereo
in the summer of 1984 (a story in its own right) and one or two
other special programs, as well as all the station's regular
audio programming. Unless someone threw it out at some point, all
that hardware used in the experimental BTSC system got crushed in
the rubble on Sept. 11, along with the transmitters themselves.
During the course of the year that the experimental
BTSC stereo system was on the air – as well as the period preceding
that when dummy-load testing was done – your writer spent at
least one overnight a week on the 104th floor of One World Trade
Center. This was frequently supplemented by trips to the World Trade
Center during the day. It was an inspiring experience to watch the
sun come up over the Brooklyn Bridge and the East River far below
– an experience that was repeated many times.
Thoughts of that very interesting period, somewhat
forgotten over the intervening years, have arisen many times since
Sept. 11. It deepened friendships with a number of TV engineers
who played parts in the ongoing story – and particularly with
Bill Steckman, an engineer who was lost on that horrible day.
In recent years, my travels seldom took me to the
World Trade Center. It did happen, however, that on Aug. 10 –
just a month before that tragic day – I took the subway to
World Trade Center where I boarded a water taxi to a marina in New
Jersey, and returned at the end of the day.
As I walked through the lobby of One World Trade Center
and through the rest of the complex, over the West Side Highway
and through the lobby of the World Financial Center to the boat,
I thought about the fact that it had been a long time since I had,
with regularity, walked through the Trade Center complex.
Little did I then know that it would be the last time
I would do so. I have not returned to the World Trade Center area
since, because somehow I can't bear the thought of seeing it
in its present state. I will never forget.
Randy Hoffner is manager of technology and strategic
planning at ABC. The views expressed in his column are his own and
not necessarily those of ABC. Write to him c/o TV Technology.
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