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![Vout = V1 2[1-Cos2ω1t]/2 + V1V2[Cos(ω2-ω1)t – Cos(ω2+ω1)t +
V2 2[1-cos2ω2t]/2
Vout = V1 2 /2 - V1 2 Cos2ω1t/2 + V1V2Cos(ω2-ω1)t
- V1V2 Cos(ω2+ω1)t
+ V2 2 /2 - V2 2 Cos2ω2t/2----2
So mixer o/p is consist of SUM & Difference (ω2+ω1) & (ω2+ω1)
Frequency component. Thus square law device acts as Mixer.](https://image.slidesharecdn.com/am-radioreceiver-130313231409-phpapp01-140920115950-phpapp01/75/AM-RadioReceiver-19-2048.jpg)
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AM RadioReceiver
- 1.
- 2. AM-RADIO RECEIVER Radioreceiver is an electronic equipment which picks up the desired signal, reject the unwanted signal and demodulate the carrier signal to get back the original modulating signal.
- 3. Function of Radio-receiver • Select desired signal and reject unwanted signal • Amplify the R.F. signal • Demodulate the selected signal
- 4. Classification of radioreceivers Radio receivers are classified according to the type of traffic they are designed to handle. • A.M. broadcast receivers • F.M. broadcast receivers • T.V. receivers • Radar receivers
- 5. Types of AM-Receiver 1.TRF-Receiver 2.Superhetrodyne AM-Receiver TRF (Tuned Radio frequency) receiver
- 6. Drawbacks of TRFReceiver • TRF receivers are simple to design and allow the broadcast frequency 535 KHz to 1640 KHz. But at the higher frequency, it produces difficulty in design. • Problem of instability. • It has poor audio quality. • B.W vary with tuning.
- 7. Super heterodyne RadioReceiver A super heterodyne receiver converts all incoming radio frequency (RF) signals to a lower frequency known as an intermediate frequency (IF).
- 8. Super heterodyne Radioreceiver with waveform at various points
- 9. SHRR with centerfreq.& B.W of each block
- 10. Advantages of SHRR No variation in bandwidth. It remains constant over the entire frequency range. High selectivity & sensitivity High adjacent channel rejection
- 11. Receiver characteristics ofthe radio 1.Selectivity : Radio receiver should have good selectivity and selectivity of radio receiver is its ability to reject unwanted signals.
- 12. 2.Sensitivity Ability toamplify weak signals. Broadcast receivers/ radio receivers should have reasonably high sensitivity so that it may have good response to the desired signal.
- 13. 3.Fidelity The fidelityis the ability of receiver to reproduce all modulating frequency equally. 1. Radio receiver should have high fidelity or accuracy without introducing any distortion. 2. Eg. In an A.M. broadcast the maximum audio frequency is 5 KHz hence receiver with good fidelity must produce entire frequency up to 5KHz.
- 14. 4.B.W.Improvement To reducethe effect of thermal noise in the performance of the receiver, it is necessary to reduce the B.W because noise is proportional to square root of B.W. Noise reduction ratio is achieved by reduction in B.W is known as the B.W. improvement B.W improv (B.I) =RF.B.W/IF.B.W Noise figure improvement = 10Log10 B.I
- 15. 6.Insertion loss •The insertion loss is the ratio of o/p power of filter (Pout) to the i/p power (Pin) for signal freq.lying within pass band of filter. • Insertion loss (I.L) = 10Log10 (Pout/Pin) 7.Dynamic Range Dynamic range is the I/P Power range over which the receiver is useful. It is in decibel. Highest range is about 100 dB
- 16. Advantages of RF-Amplifier 1.Greater gain i.e better sensitivity. 2.Improved signal to noise ratio. 3.Improved rejection of adjacent unwanted channel.i.e better sensitivity. 4.Better coupling to antenna/Good impedance matching
- 17. 2.MIXER or FREQ.CHANGER The mixer is basically a nonlinear device with two set of inputs at different frequency & one set of o/p.
- 18. In square lawmixer, square law device is used. as mixer. It is device having squared relation between i/p & o/p. Let two i/p applied to square law device are Vi = V1Sinω1t & Vosc = V2Sin ω2t --------------------1 O/P of mixer is square of sum of two i/p .i.e Vout = (Vi +Vosc )2 = Vi 2 +Vosc 2 +2 Vi.Vosc Put the value of Vi & Vso in above eqn. Vout = V1 2 Sin 2 ω1t + V2 2 Sin 2 ω2t + 2 V1V2Sinω1t . V2Sin ω2t . We know Sin 2ω1t =1-Cos2ω1t/2 & 2Sinω1t.Sin ω2t =Cos(ω2-ω1)t – Cos(ω2+ω1)t
- 19. Vout = V12[1-Cos2ω1t]/2 + V1V2[Cos(ω2-ω1)t – Cos(ω2+ω1)t + V2 2[1-cos2ω2t]/2 Vout = V1 2 /2 - V1 2 Cos2ω1t/2 + V1V2Cos(ω2-ω1)t - V1V2 Cos(ω2+ω1)t + V2 2 /2 - V2 2 Cos2ω2t/2----2 So mixer o/p is consist of SUM & Difference (ω2+ω1) & (ω2+ω1) Frequency component. Thus square law device acts as Mixer.
- 20. IF & IF-Amplifiers • Intermediate Frequency – Sum or difference in the output of a mixer that enters the IF stage. • IF amplifiers – One or more stage(s). – Provide most gain and selectivity. – IF is much lower than RF easier to design and good sensitivity is easier to obtain with tuned circuit. – IF amplifier will decide sensitivity, selectivity of the receiver. Suitable IF range is 438-465 khz. with 455khz best.
- 21. AM DETECTOR/ENVELOPE DETECTOR It produces an O/P signal that follows the envelope of the I/P AM Signal exactly. It is used in all commercial AM Radio receivers.
- 22. Automatic Gain Control If the receiver gain is const. then receiver o/p will fluctuate according to the strength of i/p signal.& this is not desirable . AGC is used to adjust the receiver gain automatically so as to keep the receiver O/P constant irrespective of the strength of I/P Signal.
- 23.