What are the limitations of TRF receiver, how these are avoided by super hetrodyne receiver?
1 Answer

- Limitations of TRF receiver:

1] TRF receiver suffers from variations in BW over the tuning range ( s 40 - 1650 KHz)

2] The gain of TRF $RX^r$ is not uniform over the tuning range.

3] The TRF is unstable at high frequency.

4] Gang tuning of more number of capacitors simultaneously is difficult.

Super hetrodyne Receiver :

  • The features of hetrodyne $RX^r$ is that all incoming radio frequency s/gs are converted into intermediate frequency, If of 455KHz usually.

  • The received s/g frequency fs, is mixed with local oscillator frequency, fo, to extract only the difference.

If = fo - fs = 455 KHz.

  • This AM wave with 455 KHz is then amplified & then fed to detector to give AF information.

  • The AF info is then amplified by v/g & power amplifier to drive the load.

SHR can overcome limitations of TRF due to the following reasons:

  • Since majority of amplification is done by IF amplifiers which are tuned by IF amplifiers which are tuned to IF, BW remains constant & therefore better selectivity can be obtained.

  • If amplifiers that provide max. gain, are tuned to IF have fixed BW $\therefore$ Gain provided is also constant over the AM tuning range.

  • The neutralization capacitor can be easily tuned to IF that is fixed $\therefore$ unwanted feedback can be eliminated and hence removes the possibility of instability at high frequency.

  • Number of capacitors which are to be tuned simultaneously are less.

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