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Engineering Extra
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The Reference Room
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Milestones
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| 'The Last Watch' |
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by Charles S. Fitch,
2.11.2004
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Charles S. Fitch, W2IPI, is a registered professional consultant engineer, member of the AFCCE, senior member of the SBE, lifetime CPBE with AMD, licensed electrical contractor, former station owner and former director of engineering of WTIC(TV) in Hartford, Conn., and WHSH(TV) in Marlborough, Mass.
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Heraclitus said the only constant is change.
Technical changes a-plenty have come to radio, but few have had more impact than the industry's move to remote controls for transmitters.
Prior to 1953, all transmitters had on-site operating engineers. These skilled folks were present to maintain standards, correct instabilities and repair and restore any plant component that might take the station off the air.
In the 1950s and '60s, various factors led to systems that allowed remote control of the transmitter. Among these factors were changes in FCC regulations to allow "off-site" monitoring and control; improvements in equipment reliability and the declining cost of gear, so that backups of critical systems could be kept online; and - as always - cost pressures.
Once more, people were asked to do more with less. Radio now saw the appearance of the combination air personality and licensed transmitter operator: the combo man.
A critical piece of equipment needed to accomplish this change was a cost-effective remote control system, reliable and accurate enough to be "legal." The Gates RDC-10 appeared and became almost ubiquitous.
Essentially an all-DC system, the studio and transmitter were tied together with two wire pairs, one for metering, the other for control. The control line actually consisted of two circuits, split into one wire and telco ground for each.
A fundamental FCC requirement for remote control was a fail-safe: If you lost connection or control of the transmitter, it had to fail in the Off mode. This was accomplished with a constant low-voltage DC "pilot" or "sealing" potential on the control pair. The pilot held closed a small relay, the contacts of which usually were in the interlock loop or filament On control of the transmitter. Lose the circuit and the transmitter went off.
The metering pair supplied DC analog for each reading calibrated against a stable reference voltage from the transmitter selected at the beginning of each meter-reading session. Channels were switched by pulses sent down the line rotating a telephone-type "step" relay reminiscent of dialing a number at the telco switch house.
Remote control is a standard configuration today even if the transmitter is in the next room. A sea change in the 1960s, it wiped out an entire job category in radio but liberated an army of talented people to make their mark elsewhere in the industry.
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