A radio-telescope measures the power, frequency spectrum and polarization of celestial sources in the radio-frequency range. In the radio-frequency range the signals from celestial sources are weaker than in the visible light.
The large wavelength of radio waves requires a large radio-telescope for a
comparable spatial resolution.
With a careful design and manufacturing of a low-noise amplifier, a band-
pass filter and a parabolic-dish primary feed we obtained a radio-telescope
with a system noise temperature of 60K in the 1.42GHz frequency range. In
the radio-telescope we employed an inexpensive commercial parabolic mirror of 3m diameter intended for satellite TV reception and corresponding
azimuth-elevation antenna positioner. We processed the signals with an
inexpensive DVB-T receiver (USB dongle) and free software running on a
portable personal computer.
With inexpensive electronics and a small antenna we observed the radia-
tion of neutral hydrogen in our galaxy Milky way. From our measurements
it is evident that Milky way has several spiral arms.
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