All RF devices and equipment should carefully observe and control their transmit power to obey with wireless communication standards and reduce RF interference with other radio devices. Power of RF signals in transmit/receive chains in wireless communication systems is measured by RF power detectors.

RF detectors are used to measure and control RF power in wireless systems. RF power detector generates DC output voltage proportional to the RF signal power at the input of detector.RF power, instead of voltage, is the primary measure of a wireless signal. In a receiver, signal strength is a critical role in maintaining reliable communications. The quantity of power transmitted is critical because of regulatory guidelines in the transmitter. Maintaining the range and quality of the radio link is also much important.

Unit of measurement of power

The unit of power is the watt. It is common in most RF and wireless applications to express power with regarding to dBm or decibels related to 1 mW

dBm = 10log [power(mW) / 1 mW]

Types pf RF detector

There are two types of RF detectors: The logarithmic type and the RMS type.

Logarithmic type

The log type produces output in terms of decibels which is a dc voltage proportional to log of input.

RMS type

The RMS detector produces a DC output proportional to the RMS value of the signal.

Application of RF detectors

It is the primarily used for transmitter output power measurement. It is necessary to know the RF output power because the application specifies it in most cases, and certain maximum values should not exceed according to Federal Communications Commission regulations. The transmitter power is controlled automatically.

As a result, power can be altered as required by comparing the calculated output power to a set point level in a feedback control circuit. In receivers, power measurement is usually defined as the Received Signal Strength Indicator (RSSI).

To control the gain of the RF/IF signal chain can be controlled and maintained a constant signal level suitable for analog-to-digital conversion and demodulation by the RSSI signal with an automatic gain control (AGC) or automatic level control (ALC).

Circuit diagram of RF power detectors