A radio-telescope for the 21cm neutral-hydrogen spectral line

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 radiation
of neutral hydrogen in our galaxy Milky way. From our measurements it is
evident that Milky way has several spiral arms.