Preamplification

A preamplifier, located at the base of the tower, employs a small, high dynamic range, monolithic amplifier with a noise figure of 3.6 db. This wide-band (1-1000 MHz) device is protected with filters to restrict its bandwidth to 3 to 45 MHz. Its gain is kept low (13 db) to avoid any possibility of overloading on strong interference. However, the gain is sufficient to overcome line losses between the antenna and the laboratory.

Before preamplification the antenna signals pass through a 10 db directional coupler for injection of calibrations. After preamplification the signals are transmitted to the laboratory through 125m of buried coaxial cable. In the laboratory a slope filter attenuates the signals below 18 MHz by 20 db. This avoids any possibility of overloading by strong, low frequency interference while the noise generated by the galactic background radiation still dominates the system noise. After 25 db of amplification in a high power amplifier, the signals are presented to a spectrum analyzer.

© Copyright Astronomical Society of Australia 1997