Antenna – Preamplifier Kits

Antenna – Preamplifier Kits

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The Antenna – PreAmplifer Kits are designed to allow for easy product selection to compare side-by-side solutions of commonly paired products. Preamplifiers are used to increase the sensitivity of the measurement. They raise the measured signal by the gain. The gain of the amplifier is subtracted from the antenna factor or subtracted from the final measurement. Not all preamplifiers are designed or intended for EMC use. Absolute EMC offers units built for this purpose, making selection easier. One only needs to be concerned with a few parameters. Key specifications of Preamps are frequency range, gain, and Noise Figure (N.F.). Other specifications may be of concern, too, depending on the application.

Frequency Range – the usable operating range of the amplifier, the amplifier can not be connected inline for use outside of its operating range; signals will not bypass the amplifier when turned off or not powered up.

Gain -  the Signal gain of the amplifier will be different across the frequency range. A calibration table is provided for each amplifier to be imported into the measurement device or software.

Noise Figure - is a normalized ratio in dB of the broadband noise the amplifier will produce when on. A lower value is better.

Maximum input power – this is the power level where the total power can not exceed the input before damage

1dB compression – this is presented in graphical or table form across the frequency range and is the input level where the amplifier is saturated with 1dB of compression. At this power level and higher levels, the amplifier is considered to be in compression, producing spurious (unwanted) signals that will appear as harmonics, and interharmonics if multiple signals are present. Input signals should not exceed this level in reducing spurious signals.

The placement of the preamplifier is an open debate. Some feel that it needs to be attached to the antenna and others feel that being outside the chamber is just as acceptable. The coax cable running from the antenna to the receiver (or measurement device) will pick up and generate noise throughout its length. This noise is low and minimal, but it does happen. If the preamplifier is placed at the end of the coax, it will amplify this noise increasing the noise floor. If the preamplifier is placed at the antenna, it has no chance to amplify this noise. The justification for attaching the preamplifier to the antenna is a valid argument. Sometimes ease of setup can overrule this benefit. At higher frequencies, where losses can be extreme, every dB counts, and moving the preamplifier to the antenna becomes more desirable.

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