T.O. 33B-1-15-265.2.1.4.3 ReceiverGainControl.NOTEThe decibel is to express the relationship between two signal amplitudes: Number ofdB = 20log10(A2/A1) where A2 and A1 are the two amplitudes that are beingcompared. Thus, dB is proportional to the logarithm (base 10) of the ratio of thetwo amplitudes. Figure 5-27 shows the relationship of dB to the amplitude ratio. Forevery 6 dB increase in Gain, the amplitude of a signal doubles. Thus, with an 18dB increase, a signal would have eight times the original amplitude. Conversely,the signal amplitude is cut in half with a decrease in Gain of 6 dB.The Gain control is used to adjust the amplitude (height) of signals on the waveform display. Normally a positiveincrease in the Gain control will increase the amplitude of the signals. However, on a few instruments the control isactually an Attenuation control, with which a positive adjustment will decrease the amplitude of the signals. Someinstruments will have both Gain and Attenuation controls. On most instruments the Gain control is calibrated in termsof the decibel (dB). Where it is not, uncalibrated slide switches or rotary knobs may be used.Figure 5-27. Decibel-to-Amplitude-RatioConversion Chart.
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