Antenna Tunner.

Antenna is basically the reciever that recieves the frequency signal.

An antenna tuner, transmatch or antenna tuning unit (ATU) is a device connected between a radio transmiter or receiver and its antenna to improve the efficiency of the power transfer between them by matching the impedence of the equipment to the antenna. An antenna tuner matches a transceiver with a fixed impedence (typically 50 ohms for modern transceivers) to a load (feed line and antenna) impedance which is unknown, complex or otherwise does not match. An ATU allows the use of one antenna for a broad range of frequencies. An antenna plus matcher is never as efficient as a naturally resonant antenna due to additional induced losses on the feed line due to the SWR (multiple reflections), and losses in the ATU itself, although issues of pattern and capture area may outweigh this in practice. An ATU is actually an antenna matching unit, as it is unable to change the resonant frequency of the aerial. Note that similar matching networks are used in other types of equipment, such as linear amplifier to match impedence
There are two types of band design in which this works.




WIDE-BAND DESIGNS:-
                                           For such wide band design we work over wide range frequency, for that purpose we need power amplifier to work over 1MHz to 30MHz. This design has a advantage of not requiring any tunning when the operating frequency is changed. This design is also used to match antenna to the transmission line.
    In the solid state RF amp design these networks because they are useful to because MOSFETs and bipolar transister are designed to operate with low resistance loads valve RF amplifier are very different because the load resistance which a valve is designed to operate with is normally much greater, hence for power designs the circuit designs are often very different.
NARROW-BAND DESIGNS:-
                                                    Devices based upon both lumped components and transmissionlines can be purchased or constructed. The most simple example of a transmission line based system is the transformer formed by a quarter wave lenght of mismatched transmission line. For example if a quarter wavelength of 75 Ω coaxial cable is linked to a 50 Ω load then the SWR in the 75 Ω quarter wavelength of line can be calculated to be 75 Ω / 50 Ω = 1.5, the quarter wavelength of line transforms this mismatched impedance to 112.5 Ω (75 Ω x 1.5 = 112.5 Ω). For more details please see the Smith chart.