Quote:
Originally Posted by Celt
The older sets had wider bandwidth because the AM band wasn't as crowded when they were made. As the band filled up with more and more stations, manufacturers had to narrow the bandwith and increase selectivity to seperate closely spaced stations, thus reducing overall fidelity. A few sets have selectable bandwidth to take advantage of better fidelity, but usually only can be used for strong local stations or clear channel stations, which there are few of these days.
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A point of interest: The days of clear channels, where only one or, at most, two stations occupied the frequency after local sunset, are a thing of the past. There are no more "clear channel" AM stations these days, due to an FCC ruling about 20 years ago which abolished that classification. Today, these former "clear" channels (a few of which are 700-760, 800, 1100, 1110-1130, 1160, 1190, et al.) are used by former daytime-only stations, which operate at lower nighttime power and often with directional signal patterns. The change was made so that the small towns/rural/suburban areas served by these stations would have local radio 24/7, rather than the local station (which in many very small towns and rural areas miles away from any large city may well be the area's only strong radio signal) signing off at sundown.
However, selectable bandwidth on some older radios could and often does improve the fidelity of local signals, as you noted. Many communications receivers designed for amateur radio have crystal filters with selectable bandwidths; the receiver (Hallicrafters SX-101A) in my first amateur radio station had a switchable crystal filter which could, at its narrowest setting, reduce the audio bandwidth to as little as 500 hertz. This is considered an optimal bandwidth for CW (Morse code) reception in the high-frequency (HF) amateur bands. My current HF amateur radio transceiver (Icom IC-725) has a fixed plug-in optional CW crystal filter, also 500 Hz if I remember correctly.