RADIO RECIEVERS

CONTENTS Introduction Tuned radio frequency receivers. Superheterodyne receivers. *block diagram *sections Rake receiver Conclusion Reference

INTRODUCTION Two basic type of radio receivers are coherent and non-coherent. In coherent the receiver must have some means of recovering received carrier and its synchronization. In non-coherent the frequencies used for demodulation are independent of transmitter’s and carrier frequencies. Two basic classification include tuned radio frequency reciever and superheterodyne receivers.

TUNED RADIO FREQUENCY RECEIVERS Earliest type It has an RF stage,detector stage,audio stage. Single channel,low frequency applications. Primary disadvantage is that their bandwidth is inconsistent and varies with centre frequency.(skin effect). 2nd disadvantage is instability due to large number of RF amplifiers. 3rd disadvantage is that their gains are not uniform.

BLOCK DIAGRAM OF TRF RECIEVER

SUPERHETERODYNE RECEIVER Non uniform selectivity of TRF led to this. Gain,selectivity,sensitivity are superior. Heterodyne means to mix two frequencies together in a nonlinear device.

Block diagram

DIFFERENT SECTIONS R-F SECTION MIXER/CONVERTER SECTION IF SECTION DETECTOR SECTION AUDIO AMPLIFIER SECTION

R F SECTION

R-F SECTION It has an amplifier and pre selector which is single or combined. Preselector is a bandpass filter with adjustable centre frequency. It provides enough band limiting to give image frequency. It is a predominant factor in determining noise figure.

Advantages of RF amplifier Greater gain, sensitivity. Improved image frequency rejection. Better signal to noise ratio. Better selectivity,

MIXER/CONVERTER Has a radio frequency oscillator stage and a mixer. Mixer converts radio frequencies to intermediate frequencies. Mixing takes place here. Original information is retained. Bandwidth is unchanged. Most common frequency is 455kHz.

I F SECTION

IF SECTION Has IF amplifiers and band pass filters. Gain and selectivity is achieved in IF section. IF centre frequency and bandwidth are constant for all stations. IF is always lower in frequency than RF and oscillations are less.

DETECTOR SECTION Converts the IF signals back to the source information. Also called as audio detector Can be either simple as a single diode.

AUDIO AMPLIFIER SECTION Has several cascaded audio amplifiers and one or more speakers. Number of amplifiers used depend on the audio signal power desired.

Rake receiver Rake receiver used specially in cdma cellular system can combained multipath component To improve the signal to noise ratio at the receiver Provide a separate correlation receiver for each of multipath signals

Multipath channel

Multipath channel Due to reflection from obstacles a radio channel can consist of many copies of originally transmitted signal Uses a multipath diversity principle it rakes the energy from the multipath propagated signal controlled

CONCLUSION Disadvantages of TRF has led to superheterodyne receivers. It is developing day by day but with no modification of basic circuit. Used for radio communication services.

REFERENCE Electronic communication system by Wayne Tomasi. http://en.wikipedia.org/wiki/radio receiver http://en.wikipedia.org/wiki/rake receiver