Do you remember
In June of 1993, the FCC issued a Notice of Inquiry (NOI) into the
rules regarding AM directional antenna performance and specifications.
This NOI was meant to provide guidance in the new world of
computer-operated systems and, in many cases, non-human supervised
systems of the time.
The original rules and the long-gone Standards of Good
Engineering Practice (that are now incorporated into the FCC's
rules) were products of the 1930s, and the rules concerning directional
antenna systems had been written mostly in 1939. Many of the DAs
designed and installed from 1939 through 1965 were located in wide-open
spaces, far from towns and other developed areas. This posed a problem
for engineers. This resulted in rules that worked, but failed to
provide the technical guidance and regulation that was required.
Therefore, in the early 1990s, the FCC adopted sweeping changes in
the AM rules. These were designed to facilitate the introduction of the
extra 100kHz at the top of the broadcast band (the so-called expanded
band), and to reduce co-channel and adjacent-channel interference. The
new rule changes reduced the amount of interference allowed. At the
time, almost every RF engineer knew of at least one case where a
directional pattern was designed to provide interference-free service,
but that satisfactory operation was hard to obtain. The new NPRM was
expected to seek a method of anticipating some of these problems, and
also trying to find better ways of calculating directional
That was then
In the early 1940s, Gates introduced the model 1D broadcast
transmitter, which a promotional flyer touted as “a moderately
priced, high-quality transmitting piece of equipment.” It
featured two doors near the top of the front panel that exposed
practically every component in the top part of the transmitter. The
full-size door provided easy access to the back.
Frequency control for the 1D was obtained from the 25-A Frequency
Control Unit, which included the oscillator and two buffer stages and
power supply with provision for operating two crystals, one being
connected for heating only.
The 1D produced 1,000W, but could be reduced to 500W or 250W for
nighttime operations. The transmitter consumed about 5.5kW or power and
responded to frequency within 1½dB from 30Hz to 10kHz. The 1D had
less than 3 percent distortion at 95 percent modulation.
It was designed to operate with a 60 to 300 ohm load and "coupled
into concentric or unbalanced low impedance transmission lines and into
most standard antennae with external matching units."
Sample and Hold
Report on the future of radio
What will be the likely impact of the new ownership rules on the
Source: Pew Research Center, July 2003 Media Update Survey
The oldest transmitter
Last year, Radio magazine asked you to help us find the
oldest transmitter that was in working condition. We located a Western
Electric transmitter in Sharon, PA, that was installed in 1940. That
transmitter is still used as a backup transmitter today. Now we want to
find the oldest transmitter in use as a main transmitter; that is, a
transmitter that is used everyday. Do you have it? Send a note to firstname.lastname@example.org and let us know. We'll
share the entries in our December issue.