What is an EMC Pre-Amplifier?
An EMC Pre-amplifier is an electronic amplifier that converts a weak signal into a strong noise-tolerant output signal, which is strong enough to be sent to an EMI receiver. It is a voltage amplifier that amplifies the voltage of the input signal. This amplifier helps to detect and measure the signal that is hidden below the noise floor of the EMI receiver. If this amplifier is not used, then the signal which is hidden below the noise floor of the receiver will not be detected. Hence, it is necessary to use the EMC pre-amplifier between the measuring equipment (for example, Near-field probes) and the EMI receiver to improve the sensitivity of the measuring process.
The enhanced system sensitivity due to high gain is very helpful when conducting EMC measurements using the Near-field probes or using antennas on an Open Area Test Site (OATS). EMC pre-amplifiers also offer flat frequency responses with a minimum deviation; hence a reduction in EMC measurement errors is ensured.
The EMC pre-amplifier is primarily used for EMC radiated emission testing as per EMC standards, such as FCC, CISPR, EN, FAA, and MIL-STD.
The key parameters to evaluate when selecting an EMC Pre-Amplifier are listed below.
Frequency: Represents the useable frequency of the EMC pre-amplifier.
Max Output Power: Represents the maximum RF power output from the pre-amplifier. It is represented in dBm.
Gain: Represents the gain of the pre-amplifier in dB.
Flatness: Represents the flatness response deviation (accuracy) in ± dB.
Noise Figure: It is the measure of degradation of the signal-to-noise ratio (SNR) (caused by components in a signal chain). It is a number. A pre-amplifier with lower values of noise figure indicates better performance.
Output Impedance: Represents the output terminal impedance of the pre-amplifier. The output impedance is usually 50 ohms.
Input Impedance: Represents the input terminal impedance of the pre-amplifier. The input impedance is usually 50 ohms.
Max Input Power: Represents the maximum RF power input that can be handled by the pre-amplifier. It is represented in dBm.
Input VSWR (typical): Represents the measure of how efficiently radio-frequency power is transmitted from the measuring equipment into the input terminal of the pre-amplifier. A low input VSWR is the indication of a good preamplifier.
Output VSWR (typical): Represents the measure of how efficiently radio-frequency power is transmitted from the output terminal of the pre-amplifier into the EMI receiver/spectrum analyzer. A low input VSWR is the indication of a good preamplifier.
Intercept point IP3 (output): IP3 is the point where 3rd order products would overtake fundamentals in output power. It is represented in dBm.
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