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What is the need for antennas what are transmitting antennas what are receiving antennas?
Wiki User
∙ 13y ago
Antennas transfer energy from a cable into the airwaves efficiently. Any transmit antenna can also be a receive antenna and viceversa. If you wish to transmit high power from an antenna, usually heat generation or high voltage is a concern that can destroy the antenna. To prevent problems, high power antennas require thicker wires and sometimes insulators to prevent overheating/burning and arcing. Many antennas can simply be made of wire of a simple length and they'll be very efficient. The length of an antenna changes it's efficiency to the cable. If you want the antenna to be efficient, you must size it to match the cable impedance. Usually the length of a single wire exiting above a metal plate is one quarter wavelength or 1/4 x 11,803/frequency in megahertz. For FM radio on an automobile, some antennas have motors that extend out of the body of the car. The height (inches) should be 1/4 x 11,803/100 megahertz or just under 30 inches. TV antennas above a house are most often a set of half wavelength wires, so change the 1/4 to 1/2 in the formula above. They use many different wire lengths to cover all the frequencies in the television band, which extends from about 50 megahertz to around 600 megahertz. Cell phone frequencies were picked partly to make the antennas small and partly so that cell phone reception can enter buildings with rebar reinforcement. Cell phone frequencies are roughly 800 megahertz and 1800 megahertz.
Receiver antennas are often made smaller than either transmit or transceiver antennas. If you open up the back of an older transistor radio, you are likely to find a bar made of ferrite material with an insulator and wire wrapped around that. The wire is wrapped a number of turns to match the impedance required by the circuit. The ferrite bar is able to focus signals to itself which in turn induces a current in the coil.
While impedance is an important issue, simple dipole antennas can be sized by the 468/Frequency in mHz formula. It will give the the length of an antenna in feet. You divide the outcome by 2 to find out what each side length should be. The impedance of an antenna can ofter be adjusted by its shape. The 90 degree V shape yields a near perfect 50 ohms impedance which is commonly used for transmitters and transceivers where as the flat top diode has a higher impedance.
The ARRL has good books on antennas. You might want to go to the library and look at a few of them.
Wiki User
∙ 13y ago
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Suppose that at the receiving node a frame's FCS doesn't match the FCS is was issued at the transmitting node what happens as a result?
The receiving nodes data link layer requests a retransmission.
What combines individual SONET signals on the transmitting end and another multiplexer separates combines signals on the receiving end?
Multiplexor
Why are audio frequencies difficult to radiate?
In order to radiate and intercept energy efficiently, the physical size of the transmitting and receiving antennas must be an appreciable portion of the E & M wavelength.An electromagnetic wave at an audio-frequency ... let's say 1 KHz ... has a wavelength of( c / 1,000 ) = ( 3 x 108 / 103 ) = 3 x 105 = 300 kilometers = about 186.4 milesEven at the nominal limit of the frequency range of hearing ... say 20 KHz ... the wavelength is( 3 x 108 / 2 x 104 ) = 15 kilometers = 9.3 miles.In order to have a fighting chance of successful radio communication at audio frequencies, over reasonable distances using reasonable transmit-power, the parties at each end of the link need antennas measured in miles.There are plenty of other great reasons that we don't use radio at the physical baseband frequencies; but even of there were no others, this reason alone is a pretty potent show-stopper.
Why collision detection is not possible in wireless network?
two reasons 1. In wireless each station has one antenna for both sending and receiving. hence we cant use the same antenna for both transmitting and at the same time detecting collisions. Further even if we have two antennas, it will be difficult to detect collision. because the transmitting signal power will be much higher than the incoming signal. hence if the sender senses signals it will fairly get a net result (an addition) of its transmitted signal and any other signal transmitted by others. it may be that its own signal is so much powerful than others that it will not recognize any collision. 2. In wireless, only the receiver is in problem. not the transmitter. so detecting for collisions at the senders end does not really make sense. we need to detect collision at the receivers end. the sender is not able to tell it whether there is a collision in receivers end. sukarna_barua@yahoo.com
Why aircraft vhf antennas are polatised vertically?
Aircraft can approach an antenna from any direction, so antennas need to be omni ("all") directional in the horizontal plane. Early on, the easiest way to get omnidirectionality was to use vertical polarisation, and it's also the simplest kind of antenna - a simple rod or wire (of the right length) works just fine. Subsequent antenna design has produced omnidirectional antennas with horizontal polarisation, but there are no significant advantages, and the design/construction is more complex than a vertical equivalent.
What acts like antennas receiving messages from as many as 10000 other cells and transmitting these messages toward the cell body?
Receptors on cell surface. Dendrites
What is fresnel zone in telecom?
Frensel Zone: Pronounced "fraynel zone." The pattern of electromagnetic radiation that is created by a transmitting station from its antenna to receiving antennas. It is in the shape of an ellipsoid, or 3D ellipse, which looks like an elongated football.
What is the use of antennas?
an antenna is used for transmitting and receiving signals with the use of electro magnetic waves. without the antenna there will not be any communication between one end and the other end. so, antennas play an important role using the EM waves. these em waves take energy from conducting electrons and transmits the information to the other end.
What is the name of the gap between the transmitting and receiving neurons?
the gooch
What is the difference between transmitting and receiving antenna?
There is no difference between the two.
What is the foreign plural of antenna?
The Latin and traditional plural is antennae. (used for insect antennae, or feelers)The common English variant is antennas. (used for radio and television antennas)
Who were The American Indians who used their native languages for transmitting and receiving messages during world war 2 were called?
it was the Comanche tribe who were used to use their native languages for transmitting and receiving messages during WWII.
Is the transmitting and receiving of data over telephone lines with the use of a modem?
fax
What is the space between the transmitting axon and the receiving dendrite or cell body?
Synapse
What must the FHSS transmitting and receiving units know to communicate?
The hopping sequence.
What is spatial multiplexing in MIMO?
MIMO is generally used for enhancing data transmission capacity, where multiple antennas are used to send the data and the more antennas means the more data transfer speed. Suppose, you have 5 antennas in the transmitting side an 5 antennas in the receiving side and you have a data stream of 100 bits for transmission. If you use each antenna to send 20 bits each then it would take five times less to send all the data if you only used a single antenna. By the use of MIMO increasing the data transmission speed is known as spatial multiplexing.
What is radiation pattern for an antenna?
Radiation pattern is just a map of how the strength of the signal varies around (transmitting) antennas. For some, like a simple whip antenna, the patttern too is quite simple. For directional antennas they can be quite complicated.
