August 1962 Electronics World
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
Electronics World, published May 1959
- December 1971. All copyrights hereby acknowledged.
August 1962 was a good month
for lovers of nomographs and infographics. Electronics World magazine published
three articles feeding the mania, including this one,
| Audio | Music Infographic, and
All make good printed references to keep on-hand. One nomograph converts the ratio
of two power levels (in watts, milliwatts, etc.) to equivalent decibels of gain.
It can also be used to find the unknown power level if one is known and the gain
in dB is known. The other nomograph facilitates graphically calculating voltage
or power based on the source resistance (assumed to have only real components; i.e.,
no complex values). If you are not sure how to keep units constant for voltage,
power, and resistance (milli, micro, etc.), calculate using the base units and then
Versatile Voltage, Power, and Decibel Nomograms
By Jim Kyle
Chart 1 - Voltage to power conversion nomograph.
Two useful charts that enable the audio technician to find amplifier gains and
losses even when voltage measurements are taken across different impedances.
Calculations of power levels and decibel ratios from voltage readings often lead
to confusion for both experienced technicians and beginners, since the conventional
formula for determining decibel ratio from voltage readings assumes that each reading
is taken at the same impedance level.
Many charts, tables, and graphs have been published to aid in solving such problems.
However, the charts shown here offer features not to be found in such previous aids.
With them, power corresponding to any voltage reading can be determined if resistance
is known, voltage can be determined if power is known, and the gain or loss in decibels
of any equipment can be determined if input and output voltages and resistance can
Chart 2 - Power (watts) ratio to decibels conversion nomograph.
Chart 1 is used for voltage-power-resistance calculations. Chart 2 converts power
levels directly to decibels gain or loss.
The voltage and resistance scales of Chart 1 bear two sets of graduations, labeled
E1 and R1 and E2 and R2 respectively. Scales bearing the same suffix number are
For example, suppose an amplifier is under test. A 10-volt signal applied to
the 500-ohm input produces an output measured at 5 volts across 8 ohms.
First, determine input power from Chart 1. The line connecting 10 volts (E2 scale)
and 500 ohms (R2 scale) passes through 0.2 watt. Output power is next. This time,
the E1 and R1 scales of Chart 1 are used, yielding an answer of 3.1 watts.
Now we turn to Chart 2. Connecting the 3.1-watt output (PI scale) and the 0.2-watt
input (P2 scale) gives a total amplifier gain of just under 12 decibels.
Nomographs / Nomograms Available on RF Cafe:
Symmetrical T and H Attenuator Nomograph
Amplifier Gain Nomograph
Voltage and Power Level Nomograph
Voltage, Current, Resistance, and Power Nomograph
Resistor Selection Nomogram
Resistance and Capacitance Nomograph
Voltage, Power, and Decibel Nomograph
Coil Inductance Nomograph
Antenna Gain Nomograph
Resistance and Reactance Nomograph
Frequency / Reactance Nomograph
Posted June 21, 2021