AM TRANSMITTER

-
Image
AM TRANSMITTER In an  AM  ( amplitude modulation )  transmitter  the amplitude (strength) of the carrier wave is varied in proportion to the modulation signal. In an FM (frequency modulation)  transmitter  the frequency of the carrier is varied by the modulation signal. There are two basic configuration for transmitters. High level modulation low level modulation  High level modulation In high power modulation signal,the carrier voltage is modulated at highest power level.the require power level is obtained by class c power amplifier.The block diagram of high level modulation as shown in fig(a). low level modulation In the low level modulation system, the carrier is modulated at low power level and the carrier power is subsequently raised to the desire level in the class B amplifier . transmitters using high power level are widely use at present .The block diagram of high level modulation as shown in fig(b). advantage AM sign
Post a Comment

LOG PERIODIC ANTENNA

-
LOG -PERIODIC ANTENNA

The log periodic antenna show in fig 1.is a multiple - element antenna the uses an entirely different principle than that of the yagi antenna.It provides good gain and wide bandwidth ,although the achievable gain is not as high as a yagi can provide for the same as antenna.The log periodic antenna consists of an array of dipoles extended along a horizontal axis. The length of each dipole is shorter than the dipole preceding it.All dipoles are connected and transmission line is connected to the shortest dipole.Maximum radiation is from the small end.



ADVANTAGE

-wide bandwidth

-same back to front ratio.

-It is design to work across wide range frequency.

DISADVANTAGE

-The VSWR performance not so good.

-low gain

APPLICATION 

-It is use in television

-It is use to measure EMC (electromagnetic compatibility) 

VIDEO OF LOG PERIODIC ANTENNA



Comments

Post a Comment

Popular posts from this blog

Psk modulation block diagram .

-
Image
Phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave) any digital modulation scheme uses a finite number of distinct signals to represent digital data. PSK uses a finite number of phases, each assigned a unique pattern of binary digits. Usually, each phase encodes an equal number of bits. Each pattern of bits forms the symbol that is represented by the particular phase. BLOCK DIAGRAM                                                                                                                                                                 FIG.1                      APPLICATION It is use in bluetooth communications It is widely  use in wirless LANs. it us use in bio-metric system. ADVANTAGE It is more power efficient modulation techniques. high data transmission. psk is less susceptible to error than ASK,while it requires/occupies same bandwi
Read more

Frequency division multiplexing (fdm)

-
Image
Frequency-division multiplexing (FDM) is a scheme in which numerous signals are combined for transmission on a single communications line or channel. Each signal is assigned a different frequency within the main channel. Transmitter Receiver       Advantage •           It does not need synchronization between its transmitter and receiver. •          Frequency division  multiplexing is simpler and easy demodulation.. •          It is used for analog signals. •          A large number of signals (channels) can be transmitted simultaneously Disadvantage   It is suffers problem of cross-talk.   It is used only when a few low speed channels are desired.   Intermodulation distortion takes place.     Application •        It is used to public telephones and in cable TV systems. •       It is used in broad casting. •       It is used in AM and FM broadcasting. Video
Read more

YAGI ANTENNA

-
Image
  YAGI ANTENNA  The location  and the length of the director and reflector element are critical, and therefore there can be more than one of each. in practice , adding more reflectors has little benefit ,so  nearly all   arrays have only one reflector element. the Yagi Uda array or simply the Yagi antenna has a single    driven element usually a ƛ/2 Dipole  or folded dipole as show in figure. the reflector is 5% longer than the driven element and space between 0.15 to 0.20 ƛ  Behind the driven element. S ingle director element, 5% shorter than the driven element is space the same distance on the other side to complete the basic Yagi antenna.Due to the relatively large physical dimensions of that elements and their spacing, the Yagi antenna is rarely used for the frequency below the VHF band.     fig (1) basic four element YAGI design fig 2 radiation pattern  Advantage -High gain -High front to back ratio - high Directivity    Disadvantage -Gain is
Read more