To understand what radio astronomy is, we need to know what electromagnetic spectrum is. We detect the World with our eyes which can only work with visible light(radiation). Moreover, visible lights is only one small part of electromagnetic spectrum. . It consists of Radio waves, microwaves, infrared, visible, ultraviolet,x-rays and gamma rays. Actually, you do not have much chance to discover something in universe with visible light. Each part of it corresponds to certain frequencies. Thus, we can explain the electromagnetic spectrum as that it is the combination of all frequencies of electromagnetic radiation. Radio astronomy is a kind of sub-branch of astrophysics which studies stellar objects with radio frequency. These objects consist of galaxies,stars,quasars,masers and pulsars.
In 1860, theoretically , Maxwell’s equations show that the electromagnetic radiation is bound with magnetism and electricity. Moreover, it could be with any wavelength. In experimentally the first discovery of radio waves source is made by Karl Jansky, who worked in Bell Telephone Laboratories as an engineer, in 1930. He worked on interfered with short wave transatlantic voice transmissions with large antenna. He realised that his analog pen-paper system recorded a repeated signal of indistinct origin. He also realised that the signal peaked about per 24 hours. Thus, he thought that it could be sun. However there was a problem that the signal repeating cycle is 23 hours 56 minutes. At this point his friend, Albert Melvin Skellet, disclosed that this cycle was the certain lenght of the sideral day. So they decided that if the source was astronomical, it should be passing in front of the antenna once every Earth rotation. Then, Jansky found that rediation peaked whenever the antenna was aimed to the densest part of the Milky Way. The source was assigned Saggitarius A. He pronounce the discovery in 1933 and wanted to work on Milky Way in detail. However, Bell Labs take him to other Project. After Jansky, Grote Reber built a parabolic radio telescope in 1937 and observed the same things with Jansky. Moreoever, he conducted the first research in the radio astronomy. In 1942, British Army officer, J. S. Hey, announced his detection of Sun’s radio waves.
EM consist of all types of radiation. We can explain the radiation as a energy that moves and spreads out like a light come from lamp. EM can be shown in terms of wavelenght(m), energy(Ev) or frequency(Hz).
Radio Waves : The frequencies are between 3 THz and 3KHz .In daily life, they are generally used for communication, radar, broadcasting, navigation systems etc.
Microwaves : The frequencies are between 300 GHz to 300 MHz. They are used for communication, navigation, radar, radio astronomy, heating and power application, spectroscopy etc.
Infrared: The frequencies are between 430 THz to 300 GHz. They are used for thermography, meteorology, health hazard, night vision, biological systems, tracking etc.
Visible: The frequencies are between 430 THz and 470 THz. They consist of 6 main color which have different frequencies.
Ultraviolet: The frequencies are between 750 THz and 30 PHz. They are used for photography, chemistry, air purification, herpetology, electric and electronic industry etc.
X-Rays: The frequencies are between 30 PHz and 30 EHz. They are used for radiographs, computed tomography, radiotherapy, security, x-ray crystallography etc.
Gama Rays : Their frequencies are typically over 10 EHz.
Radio telescopes are constructed to receive radio waves from space. In the basic form, it needs three components. There can be any number of ANTENNAS to collect the datas(radio signals). Many of them are parabolic dishes to reflect the signals to a receiver. A RECEIVER and AMPLIFIER to increase the weak radio signals to a suitable level. A RECORDER saves a signals to be analysed by physicist. In complex form, it needs ;
The antenna is the main part of a radio telescope. Most of them are quite large for resolving power. Larger ones can better focus the energy from a smaller region on the space. Most used antenna is the parabolic dish antenna but also many other types are used. For example,large arrays of dipole antennas are used to search pulsars. Moreover antennas have dish. The size of it is important because the dish determines the amount of collected radiation. If the collecting area becomes larger, the weaker source can be detected.
The signals which are came from space are often very weak. To analyse them, we need to amplify signals by milions of times. So, we can define the role of pre-amplifier as to increase this signals many times with adding little noise. The pre-amplifier is usually called LNA(low noise amplifier).
The main role of the mixer is to decrease the frequency of the coming signal from the pre-amplifier. It is did for some reasons. First of all, it is hard to make well amplifiers, filters and some equipments for high frequency. Secondly, ıf amplifying process is done with frequency which we are receiving, the amplified signal can escape back into our antenna and create feedback. The mixer take the signals from oscillator and the signal from pre-amplifier to create two additional outputs. One of them is at the input signal frequency minus oscillator frequency. The other one is at the sum of input signal and oscillator.
The role of the local oscillator is