The Radioman's Manual of RF Devices, Principles and Practices
Dealing with the RF aspects of radio communication, this is an indispensable book for anyone involved in land mobile radio, ham radio, marine radio or aviation radio.
TABLE OF CONTENTS The Radioman's Manual of RF Devices, Principles and Practices
Chapter 5: Test and Measurement Accessories
There are numerous test and measurement accessories that you will need when performing various RF test and measurement techniques. Most of these devices are passive in nature. However, in order to properly use these RF test accessories, it is important to understand just how these devices operate. This chapter explains how to use test accessories and, where appropriate, a detailed description on how to check test devices is included.
5.1 Dummy Loads
When testing a transmitter, it is important to direct the power output into a 50-ohm dummy load instead of an antenna. The dummy load must be capable of dissipating the rated power of the transmitter and should allow little radiation beyond the immediate test area. A typical dummy load is shown in Photo 5 1. This is a dry dummy load, which is capable of dissipating up to 200 watts. Dry dummy loads have large radiating fins to radiate the heat. Dry loads can be operated in any position and are easier to transport since there is nothing to leak.
Photo 5 1: This dry dummy load is capable of dissipating 200 watts of power. It can be operated in any position. (Courtesy Coaxial Dynamics, Inc.)
Some dummy loads use oil to keep the resistive element cool. Oil-filled dummy loads are usually rated at higher power dissipation than the dry loads. The obvious disadvantage is that they can leak oil if allowed to turn over. Photo 5 2 shows an oil-filled dummy load.
Photo 5 2: This oil-filled dummy load can dissipate...
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