The CALLISTO spectrometer is a programmable heterodyne receiver built in the framework of IHY2007 and ISWI by former Radio and Plasma Physics Group (PI Christian Monstein) at ETH Zurich, Switzerland.

The main applications are observation of solar radio bursts and rfi-monitoring for astronomical science, education and outreach. The instrument natively operates between 45 and 870 MHz using a modern, commercially available broadband cable-TV tuner CD1316 having a frequency resolution of 62.5 KHz.

The data obtained from CALLISTO are FIT-files with up to 400 frequencies per sweep. The data are transferred via a RS-232 cable to a computer and saved locally. Time resolution is 0.25 sec at 200 channels per spectrum (800 pixels per second). The integration time is 1 msec and the radiometric bandwidth is about 300 KHz. The overall dynamic range is larger than 50 dB.

Many CALLISTO instruments have been deployed worldwide, including 5 spectrometers in India (2 in Ooty, 1 in Gauribidanur, 1 in Pune, 1 in Ahmedabad), one in Badary near Irkutsk, Russian Federation, two in South Korea, three in Australia (Perth, Melbourne and Heathcote), two in Hawaii, two in Mexico, one in Costa Rica, two in Brazil, three in Mauritius, 5 in Ireland, one in Czech Republic, two in Mongolia, four in Germany, two in Alaska, two in Kazakhstan, one in Cairo, one in Nairobi, one in Sri Lanka, three in Trieste, one in Hurbanovo/Slovakia, two in Belgium, two in Finland, 8 in Switzerland, one in Sardinia, 4 in Spain, 5 in Malaysia, 3 in Indonesia, one in Scotland/UK one in Roztoky/Slovakia, one in Peru, one in Rwanda, one in Pakistan, 2 in Denmark, one in Japan, one in South Africa, two in Greenland, two in Austria and one in Uruguay.

Through the IHY/UNBSSI and ISWI instrument deployment program, CALLISTO is able to continuously observe the solar radio spectrum for 24h per day through all the year. All Callisto spectrometers together form the e-Callisto network. Callisto in addition is dedicated to do radio-monitoring within its frequency range with 13’200 channels per spectrum. The frequency range can be expanded to any range by switching-in a heterodyne up- or a down-converter.
Instrument deployment including education and training of observers was financially supported by SNF, SSAA, NASA, Institute for Astronomy and North-South Center of ETH Zurich and a few private sponsors.