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RF Power Measurements In The Field

Source: Bird

By Lynn Strube, Bird

Introduction

There are many valid reasons to make RF power measurements in a field environment. It may be difficult to actually select the top reasons but I feel reasonably comfortable in selecting some important reasons to make a field power measurement.

Validation of Manufacturer

Any transmitter manufacturer producing a high quality product goes to great extremes and expense to ensure that their product meets the RF power output that it was designed and marketed for. In other words a customer expects a transmitter designed and manufactured to produce a reliable 5kW signal to meet published specifications. Transmitter manufactures use a variety of methods when calibrating RF power in their factory settings, depending on the ratings and purpose of their product. If the transmitter is a vehicle radio capable of producing 50 watts then a relative small test load can be used to terminate the output power and an inline directional wattmeter can be used to calibrate the power output. Some manufacturers also choose to use a directional coupler, terminating sensor and a display meter to set RF power. A high power transmitter capable of 50kW will, more than likely, be using a water cooled load and to set the power a calorimetric calculation will be used. These are naturally pristine environments where the highest quality standards are met and the use of lab quality instruments is expected and utilized on a daily basis. Many manufactures also adhere to ISO test, manufacturing, and quality standards. That would require all of their test equipment to be calibrated on a specified time cycle and the data is recorded thus ensuring all of their equipment in use meets published quality standards.

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