With a 10 m large diameter the parabolic antenna reflector gives a theoretical gain of 40 dB on 1,4 GHz band. The parabola focus is located 5 metre distant from the source cavity handled by the mast boom and holding a dipole that is the receiving part of the antenna. Signals captured by the dipole are conducted to an SDR receiver via a coaxial cable. Despite this cable is a low loss one, a certain level of signals is lost and some noise added due to the length of the cable. The best strategy is thus to amplify the signal by inserting a preamplifier as close as possible to the receiving dipole.
Temporarily two amplifiers have been installed at a few metres from the source. The first is a KU LNA 133BH. Its characteristics are displayed on next figure.
Intrinsic preamplifier noise factor, important for overall radiotelescope receiving performances is displayed on the left scale. Gain is given on the right scale.
Second preamplifier is behind the first one just after a 1350-1450 MHz band pass filter.
It is providing a significant improvement in receiving performances, on dongle SDR key receiving performance at 1240 MHz.
Preamplifier will be soon replaced by an even better one dedicated to radioastronomy.