SBE Certification Handbook for Radio Operators by Bartlebaugh Ron

Author:Bartlebaugh, Ron [Bartlebaugh, Ron]
Language: eng
Format: epub
Publisher: Society of Broadcast Engineers, Inc.
Published: 2015-02-14T16:00:00+00:00

Figure 4-37a A plate voltage meter reading 3 kilovolts.

Figure 4-37b A plate current ammeter reading 3 amperes.

Performing the math of multiplying 3000 volts times 3 amperes renders a transmitter power input calculation of 9,000 watts or 9 kilowatts (kW). Every transmitter manufacturer publishes an efficiency factor in terms of percentage for each of its transmitters. For study purposes, let’s assume that a particular transmitter’s efficiency factor is 81%. The efficiency factor means that a transmitter will output 81% of its power input whereas the remaining amount of power will be lost in dissipated heat. To calculate the transmitter’s power output using the indirect method one would multiply the voltage times the current times the efficiency factor.

Therefore, when we multiply the transmitter’s 9kW of input power as calculated above by 0.81 (the efficiency factor) we learn that the transmitter’s indirectly calculated power output would be 7,290 watts or 7.29 kilowatts.

Many newer transmitters are solid-state designs and use transistors in their final RF amplifier stage rather than tubes. Instead of a plate element like a tube has, transistors have an element termed a collector. On a solid-state transmitter there will be a collector voltage indicator and a collector current indicator. Solid-state transmitters also have some loss due to heat dissipation, therefore they also have a published efficiency factor.

The method of calculation of indirect power for a solid-state transmitter is to multiply its collector voltage times its collector current times its efficiency factor. For example, if a solid-state transmitter has a collector voltage of 100 volts, a collector current of 40 amperes, and an efficiency factor of 87%, its indirect power output calculation would be 3,480 watts or 3.48 kilowatts (100 x 40 x 0.87). The formula for calculating indirect power for a transmitter is shown in Figure 4-38 below.

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