Radio-frequency transducers
The term radio-frequency (RF) transducer is a fancy name for the antenna. Antennas are so common that you probably do not think about them often. Your car radio has one. The portable headphone radio, which you may use while jogging on a track, employs one. Cellular /cordless telephones, portable television receivers, and handheld radio transceivers use antennas. Hundreds of books have been written on this subject.
There are 2 basic types of RF transducer:
-Receiving antenna
-Ttransmitting antenna.
A receiving antenna converts electromagnetic (EM) fields, in RF range from around 9 kHz to several hundred gigahertz, into alternating current signals that are amplified by receiving apparatus. A transmitting antenna converts powerful alternating currents into EM fields, which propagate through the space.
There are a few significant differences between receiving antennas and transmitting antennas designed for the specific radio frequency. The efficiency of an antenna is significant in transmitting applications, but not so significant in reception. Efficiency is percentage of power going into a transducer which is converted into desired form. If input power to a transducer is P in watts and output power is P out watts, efficiency of it in percent, Eff , can be found by using the following % equation:
Eff % = 100 Pout /Pin
Problem:
In the transmitting antenna, 75 W of RF power are delivered to transducer, and 62 W are radiated as an EM field. What is the efficiency of transducer?To solve this problem, plug numbers into formula. In this particular case, Pin=75 and Pout=62. Thus,
Solution:-
Eff%=100X62/75=100X0.83=83 percent
The other difference between transmitting and receiving antennas is the fact that, for any given frequency, transmitting antennas are larger than the receiving antennas. Transmitting antennas are more critical as to their location. Whereas a small loop or whip antenna may work well indoors in the portable radio receiver for frequency modulation (FM) broadcast band, same antenna would not function well at broadcasting station for use with transmitter.
Still another difference between transmitting and receiving antennas involves power-handling capability. Apparently, very little power strikes the antenna in a wireless receiver; it can be measured in fractions of a microwatt. But, a transmitter might produce kilowatts or even megawatts of output power. A small loop antenna, for example, would get hot if it were supplied with 1 kW of RF power; if it were forced to deal with the 100 kW, it would melt probably.