Orban Optimod-AM 9400, Operating Manual

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INTRODUCTION ORBAN MODEL 9400
vents simultaneous remote and local control.
See Security and Passcode Programming (starting on page 2-43) for more detail.
Why the North American NRSC Standard?
Over the years, as the North American airwaves have become more crowded, inter-
ference from first and second adjacent stations has become more and more of a
problem. Receiver manufacturers responded by producing receivers with decreased
audio bandwidth so that an adjacent station's modulation extremes would not be
audible as interference. This cutting of the bandwidth had the effect of reducing
the receiver's high-frequency response, but it was felt that lower fidelity would be
less obnoxious than interference. As long ago as 1978, Orban proposed and imple-
mented pre-emphasis and low-pass filtering for AM broadcast to provide brighter
sound at the receiver while minimizing interference. This approach has become
widely accepted. The NRSC-formalized standard is acceptable to all industry seg-
ments, and when implemented, can result in a vast improvement in AM radio.
AM Stereo Introduces a Pre-emphasis Dilemma
Certain AM receivers manufactured since 1984 for sale in North America, particularly
those designed for domestic AM stereo reception, have a frequency response that is
substantially wider than that of the typical mono AM receiver. The frequency re-
sponse was widened largely to enhance the sales potential of AM stereo by present-
ing a dramatic, audible improvement in fidelity in the showroom. As these new re-
ceivers became more prevalent, broadcasters had to choose whether the station's
pre-emphasis would be optimized for the new AM stereo receivers or for the exist-
ing conventional receivers that form the vast majority of the market. If the choice
was for conventional receivers (which implies a relatively extreme pre-emphasis), the
newer receivers might sound strident or exceptionally bright. If the choice favored
the newer receivers (less pre-emphasis and probably less processing), the majority of
Audio Frequency (kHz)
10 11 12 13 14 15
Relative Amplitude (dB)
-50
-40
-30
-20
-10
0
Stopband Area
Modulation
10.5
1%
3.2%
0.32%
10%
31.6%
100%
Figure 1-3: NRSC Lowpass Filter