We don’t know what happened to the last L in Bell’s name. That was the year Bell telephone introduced the Transmission Unit (TU) which was later (in 1928) called a bel, to honor Alexander Graham Bell (the chap on the left). There was an elaborate definition of what a standard cable was and 1 MSC was the amount of loss of a predefined signal over a mile of this cable. Originally, the unit used to measure loss in telephone and telegraph cables was “miles of standard cable” (MSC). The decibel can trace its roots back to the old phone system. This holds true whether or not those knobs go up to eleven. A linear pot would seem off because, for example, a tenth of a turn at one extreme will affect the apparent volume much more than a tenth of a turn at the other extreme. This is also why potentiometers made for volume controls have a logarithmic taper. That ratio is about 1 trillion to 1, but that’s only 120 dB. That is to say, you can hear a whisper or a space shuttle launch. Your ear, for example, has a huge dynamic range. The reason is that human ears and eyes have a logarithmic response to those quantities. It’s all about logarithms, and this ends up being extremely useful when measuring something like antenna or amplifier gain.īesides antennas, decibels are often used to measure sound and light. Doubling the number of decibels doesn’t double the ratio, as you will soon see. Sometimes in electronics, we deal with really large ratios, so the decibel is logarithmic to cope with this. If you are versed in metric, you won’t be surprised to learn a decibel is 1/10 of a bel. Actually, the real measure is a bel, but you almost never see that in practice. If you’ve hung around electronics for any length of time, you’ve surely heard of the decibel (often abbreviated dB). The decibel is a measure of a power ratio.
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