About my radiotelescope:
Specifications:

Diameter: 3m
Frequency: 1420MHz
Beam width: 4.9 degrees
Gain: 32dB
F number: 0.4

Goals

The goal of building this radio telescope is to observe the 1420MHz radiation from space , hydrogen line. Radiation of this frequency is produced in the interstellar coulds of hydrogen gas when an electron in a neutral hydrogen atom changes its spin. There is a difference in energy for an electron with spin "up" state, and spin "down" state. Energy difference when an electron changes its state is radiated in a form of electromagnetic radiation at a frequency of 1420MHz.

Exact frequency of the radiation is 1420.406 MHz for stationary observer. For non stationary observer there will be apparent frequency shift. Frequency will shift towards higher frequency if the observer is moving towards the radiation source, and it will shift towards lower frequency if the observer if moving away from the source. The name for this effect is Relativistic Doppler effect. By calculating Doppler effect from various parts of our galaxy it's possible to calculate rotational speed.

Rotational speed of the galaxy should be inversly proportional to distance from the center of the galaxy. But measurements show that it isn't. It appears there is a lot more mass in the galaxy that we can't see. That mass is called Dark matter. By observing and calculating rotational speed of our galaxy, we can indirectly detect dark matter.