|Paul Riemers, Ronald Halfwerk
| In most of our systems, we are pretty allergic to noise. During the development of our receivers, much effort is put in keeping the noise level as low as possible, in order to gain sensitivity. But occasionally noise might be beneficial to your system, and in this case we deliberately will add some noise at a substantial level.
This noise source was built for the focal plane array antennas of APERTIF in the Westerbork telescopes. It will be placed on the reflector surface, together with control circuitry, a thermostat and an antenna. In this way a calibration signal will be transmitted towards the receiver elements. The source will deliver -65 dBm onto the antenna over a usable band between 500 MHz - 2 GHz. Special care has been taken to maintain the stability of the output level.
Beam forming with phased array antennas only will become efficient if the gain en phase of each signal path is well known. In the case of APERTIF's Vivaldi array, we're dealing with 121 elements! Periodically the receiver will refer to this stable source, so compensation for gain and phase drift can be performed. Needless to say this noise source can be silenced to become invisible during normal use.
Btw, 'In Visible Silence' is referring to an album of the British band Art of Noise: groundbreaking sampling sound pioneers knowing the formula of exploiting randomly selected samples, used partly to set up a rhythmic groove, partly to pepper it with oink-oinks to keep the listener intrigued. History of radio astronomy already did convince people that a particular collocation of different samples might be considered also as 'art' (of noise or whatever else).
|fotos: ASTRON - P. Riemers, R. Halfwerk