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# Amplifier Gain NomogramAugust 1965 Electronics World

 August 1965 Electronics World   Table of Contents Wax nostalgic about and learn from the history of early electronics. See articles from Electronics World, published May 1959 - December 1971. All copyrights hereby acknowledged.

Even with the ready availability of programmable calculators and smartphone apps, there are still times when having a handy-dandy nomograph printed out and hanging on the wall for quick reference can be a great asset. This nomograph which appeared in a 1965 issue of Electronics World magazine provided ready conversion between two different (input and output) voltage and power values to equivalent decibel values. It seems strange that the watts and voltage scale is on the left and the milliwatts and millivolts scale is on the right. That might be more intuitive for a nomograph of attenuation, but not - at least to me - for positive gain as through an amplifier.

Amplifier Gain Nomogram

By Max H. Applebaum

Warwick Electronics, Inc. Pacific Mercury Div.

Power and voltage gain of amplifiers with equal input and output impedances are readily found.

To find the power gain of an amplifier, it is necessary to compute the ratio of its output to input power, take the log and multiply by 10. When the input and output resistances are equal, the voltage gain of the amplifier can be calculated by multiplying 20 times the log of the ratio of output to input voltages.

This nomogram eliminates the tedious calculations involved, and gain can be determined in a much simpler manner.

For values of 10n or 10-n times those on the E1 scale, subtract or add, respectively, n times 20 db from or to the values on the voltage-gain scale. (n times 10 db from or to the power-gain scale when the P1 scale is used.)

For values of 10n or 10-n times those on the E2 or P2 scales, add or subtract respectively n times 20 db to or from the values on the voltage-gain scale and n times 10 db to or from the values on the power-gain scale.

Example: Find the voltage gain of an amplifier whose input and output resistances are equal, when 6 volts output is measured for 200 mv. input.

Solution: Place one end of a straightedge over 6 on the left-hand scale and the other end over 200 on the right-hand scale. Find 29.6 at the point where the straightedge crosses the center scale. This is the voltage gain in db.

Posted September 12, 2022
(updated from original post on 6/4/2015)

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