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 » project in 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 and we had only information about system temperature of 150° K (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 travel down to the receiver located 15 meter down. We have set at this location a préamplificateur KU LNA 133BH with a gain of 30 dB and a noise figure of 0,7 dB at 1440 MHz in front of an SDR receiver. 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 12.7 dB 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 SKU: RAS-1420LNA-CBPF preamplifier designed for radio-astronomy with a CAVITY BAND PASS FILTER N/F of 0.29 +/- 0.15 dB, gain of 35 dB +/- 3 dB.
La Villette radiotelescope has just delivered its first image built after spectal analysis of hydrogen band radio signals. The spectrogram image represents the intensity of signals during 24 hours from july 30 to 31, 2019.
Rémi F6CNB/N5CNB computed the spectral density of radio signals every minute during 24 hours between 1419,50 and 1421,50 MHz frequencies. Every image pixel represents integrated signal power density over a 3906 Hz bandwidth during 60 secondes. Time is along vertical axis and frequencies are on horizontal axis. Pixel colors represent the spectral density. Calibration is not yet performed.
As the radiotelescope is blocked in vertical position aiming at zenith, the Earth rotation induces a 360° per 24 hours sky sweep corresponding to an angle of 0,25 degrees per minute. Thus, the image vertical axis also represents 360° and each pixel 0.25 degrees. The antenna aperture angle, related to its 10 metre diameter, is close to 1 degree at 1420,4 MHz. Consequently, verticaly four image pixels cover globally the same 1 degree sky area during four minutes.
Dimension Parabole project team will report the progress in radiotelescope observations when the 33 years old preamplifier located at antenna dipolar source is replaced by a one with better quality noise figure