In Paris La Villette parc, the radiotelescope has been activated Sunday July 21, 2019, thirty years after it was built.
While the radio-telescope was settled in Paris La Villette Parc 33 years ago it had never been used and all its electronic parts dismantled and electric main power removed soon after. Read the full story about the « Stars song » projecton the introduction page of this site describing the effort of rehabilitation accomplished by Dimension Parabole association since 2018. Based on our recent knowledge of the existence of a transistor MOS-FET preamplifier located near the antenna dipolar source, we tentatively applied a 10-15 Volts continuous voltage to the coaxial cable descending from the source cavity in order to power it. In the 80’s a MOS-FET transistor preamplifier was the most performing device available. We did not have informations about its gain performance. We only had an information about its 1.5 dB noise figure.
We happily observed that an electronic device was indeed connected to the coaxial cable 7 metres above the insertion point when reading that a 100 mA current was delivered by the power supply as soon as applying more than 10 V DC (10-18 V).
Then Rémi F6CNB/N5CNB used a 500 KHz-1,6 GHz spectrum analyzer connected to the antenna in order to measure the signal power received by the dipole antenna through the coaxial cable. A test pulse signal was sent at the same time by the analyzer through a second coaxial cable to a dipole located at the center of the parabolic dish reflector. This dipole had been designed for receiving calibration purpose.
The following picture displays the level of received signal while the remote preamplifier was not powered by a continuous voltage.
Power supply voltage was then injected into the coaxial cable through a special device for applying the voltage to the remote MOS-FET preamplifier and at the same time let the radio signal go down to the receiver located 15 meter down. We have set at this location an SDR receiver behind a second preamplifier with a gain of 25 dB and a better low noise figure. Resulting signal level measured by SDR was -77,3 dB as shown on next picture when remote MOS-FET preamplifier was not powered.
Alternately, when DC voltage was applied to remote preamplifier, received signal raised to a level of -64,6 dB. The difference (77,3 – 64,6) translates the remaining gain of 12,7 dB due to conducting loss into the 15 m coaxial cable. This loss is probably greater than 12 dB for if we do not insert the supplementary local preamplifier, we do not observe any change in the signal level measured by SDR receiver while remote preamplifier was powered. There is no doubt that a better result will be achieved when the second preamplifier is installed closer to receiving dipole. Lately the MOS-FET preamplifier will also be replaced by a one designed for radio-astronomy with a better noise figure.
We will report our progress in reception performance and results when preamplifiers are set closer to source antenna.