Ham Radio General Class Practice Test

What type of instrument can be used to accurately measure an RF field?

1. A receiver with an S meter

2. A calibrated field-strength meter with a calibrated antenna

3. A betascope with a dummy antenna calibrated at 50 ohms

4. An oscilloscope with a high-stability crystal marker generator

The correct answer is: A calibrated field-strength meter with a calibrated antenna

A calibrated field-strength meter with a calibrated antenna is specifically designed to accurately measure radio frequency (RF) fields. This type of instrument measures the strength of the electromagnetic field in decibels relative to a specific reference level. The calibration ensures that the readings are accurate and can be trusted for both practical applications and regulatory purposes. The use of a calibrated antenna is crucial because the antenna must be properly matched and calibrated to ensure that it accurately picks up the RF signals in the environment. By knowing the characteristics of both the meter and the antenna, you can obtain precise measurements of the field strength at a specific point in space. In contrast, a receiver with an S meter may provide some indication of signal strength, but it is not a dedicated measurement tool for RF fields. A betascope, while useful in other contexts, is not designed for RF field strength measurements. Likewise, an oscilloscope typically displays waveforms and does not directly measure field strength, even if it can analyze signals in terms of voltage or time. Thus, the combination of a calibrated field-strength meter and a calibrated antenna provides the correct means for accurately measuring RF fields.