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- 2. Noise Suppression Effects of FM ● Noise from lightning, motors, and any power line switching that produces transient signals. ● Noise is typically narrow spikes of voltage with very high frequencies. ● FM radio has a special limiter circuit that cuts off these spikes. ● The important information in FM radio is carried by changes in frequency, not by the signal strength. ● So, cutting off the spikes (amplitude variations) doesn't affect the information. ● This is why FM radio is better than AM radio at handling noise - it cuts out the noise without losing the signal.
- 3. Noise Suppression Effects of FM ● Noise from lightning, motors, and any power line switching that produces transient signals. ● Noise is typically narrow spikes of voltage with very high frequencies. ● FM radio has a special limiter circuit that cuts off these spikes. ● The important information in FM radio is carried by changes in frequency, not by the signal strength. ● So, cutting off the spikes (amplitude variations) doesn't affect the information. ● This is why FM radio is better than AM radio at handling noise - it cuts out the noise without losing the signal.
- 4. Noise Suppression Effects of FM ● Noise from lightning, motors, and any power line switching that produces transient signals. ● Noise is typically narrow spikes of voltage with very high frequencies. ● FM radio has a special limiter circuit that cuts off these spikes. ● The important information in FM radio is carried by changes in frequency, not by the signal strength. ● So, cutting off the spikes (amplitude variations) doesn't affect the information. ● This is why FM radio is better than AM radio at handling noise - it cuts out the noise without losing the signal.
- 5. Noise Suppression Effects of FM ● Noise from lightning, motors, and any power line switching that produces transient signals. ● Noise is typically narrow spikes of voltage with very high frequencies. ● FM radio has a special limiter circuit that cuts off these spikes. ● The important information in FM radio is carried by changes in frequency, not by the signal strength. ● So, cutting off the spikes (amplitude variations) doesn't affect the information. ● This is why FM radio is better than AM radio at handling noise - it cuts out the noise without losing the signal.
- 6. Noise Phase Shift ● Noise can cause small wobbles in the FM signal, even though FM is good at rejecting noise. ● Imagine the signal and noise as arrows. The size of the arrow represents strength, and the direction represents its effect. ● Normally, noise is like a bunch of small arrows spinning in different directions. ● But to simplify things, we can imagine noise as just one strong, spinning arrow. ● The combined effect of signal and noise creates a new, bigger arrow that wobbles slightly. ● The maximum wobble happens when the noise arrow is perpendicular to the signal arrow.
- 7. Noise Phase Shift ● Noise can cause small wobbles in the FM signal, even though FM is good at rejecting noise. ● Imagine the signal and noise as arrows. The size of the arrow represents strength, and the direction represents its effect. ● Normally, noise is like a bunch of small arrows spinning in different directions. ● But to simplify things, we can imagine noise as just one strong, spinning arrow. ● The combined effect of signal and noise creates a new, bigger arrow that wobbles slightly. ● The maximum wobble happens when the noise arrow is perpendicular to the signal arrow.
- 8. Noise Phase Shift ● Noise can cause small wobbles in the FM signal, even though FM is good at rejecting noise. ● Imagine the signal and noise as arrows. The size of the arrow represents strength, and the direction represents its effect. ● Normally, noise is like a bunch of small arrows spinning in different directions. ● But to simplify things, we can imagine noise as just one strong, spinning arrow. ● The combined effect of signal and noise creates a new, bigger arrow that wobbles slightly. ● The maximum wobble happens when the noise arrow is perpendicular to the signal arrow.
- 9. The amount of signal distortion caused by noise depends on a few things. • Higher frequencies are more affected: The higher the frequency of the information being carried by the FM signal, the worse the wobble caused by noise will be. • Severity depends on allowed frequency range: FM signals can change frequency within a certain limit. If this allowed range is large (high modulation index), even a wobble caused by noise might be too small to matter. But if the allowed range is small (low modulation index), noise can cause a bigger wobble and potentially distort the signal more. • Noise is usually brief: The good news is that noise spikes are usually very short-lived. So, even if they cause a wobble, it's usually just for a moment. • Impact on intelligibility: In most cases, even with heavy noise, the wobble won't be bad enough to completely garble your speech. It might sound a little
- 11. Preemphasis • Noise messes with FM, especially high frequencies: Noise spikes have a lot of high-frequency content which can overpower the actual high-frequency parts of the signal you want to transmit (like high- pitched sounds or musical instruments). This distortion can make the signal unintelligible. doesn't need much high frequency: Most of what we say in speech is at lower frequencies. So, for voice calls, FM can handle noise pretty well even without needing all the high frequencies. frequencies for quality: Instruments use high frequencies to create their unique sounds. To transmit high-fidelity music, you need a wider range of frequencies, including those high frequencies. But these high frequencies are also weak, and noise can easily wipe them out.
- 12. Preemphasis De-emphasis at transmitter ● A de-emphasis circuit is used at the receiver to return the frequency response to normal. ● It's a simple low-pass filter with the same time constant (75 μs) as the pre-emphasis circuit. ● This results in a cutoff frequency of 2123 Hz for the de-emphasis circuit. ● Frequencies above this cutoff are attenuated at 6 dB per octave. ● The de-emphasis effectively cancels out the pre-emphasis, providing a flat frequency response overall.
- 13. Preemphasis ● Pre-emphasis boosts high frequencies before sending: To combat this, FM radio uses a trick called pre-emphasis. It boosts the high frequencies of the signal a bit before sending it out. This way, even if noise messes with them, they're still strong enough to be received clearly. ● De-emphasis weakens high frequencies at receiver: There's a matching process at the receiver called de-emphasis. It weakens the high frequencies a bit to bring them back to their normal level and prevent them from overpowering the lower frequencies
- 14. Preemphasis Pre-emphasis at transmitter ● This circuit boosts high frequencies before sending the signal. ● This is achieved using a simple RC high- pass filter with a time constant (τ) of 75 μs. ● The chosen time constant results in a cutoff frequency (fL) of approximately 2123 Hz. ● Frequencies above fL are boosted at a rate of 6 dB per octave. ● Strengthens high frequencies in the signal
- 15. Preemphasis Pre-emphasis at transmitter ● This circuit boosts high frequencies before sending the signal. ● This is achieved using a simple RC high- pass filter with a time constant (τ) of 75 μs. ● The chosen time constant results in a cutoff frequency (fL) of approximately 2123 Hz. ● Frequencies above fL are boosted at a rate of 6 dB per octave. ● Strengthens high frequencies in the signal
- 16. Preemphasis Pre-emphasis at transmitter ● This circuit boosts high frequencies before sending the signal. ● This is achieved using a simple RC high- pass filter with a time constant (τ) of 75 μs. ● The chosen time constant results in a cutoff frequency (fL) of approximately 2123 Hz. ● Frequencies above fL are boosted at a rate of 6 dB per octave. ● Strengthens high frequencies in the signal
- 17. Preemphasis Pre-emphasis at transmitter ● This circuit boosts high frequencies before sending the signal. ● This is achieved using a simple RC high- pass filter with a time constant (τ) of 75 μs. ● The chosen time constant results in a cutoff frequency (fL) of approximately 2123 Hz. ● Frequencies above fL are boosted at a rate of 6 dB per octave. ● Strengthens high frequencies in the signal
- 18. Preemphasis De-emphasis at transmitter ● A de-emphasis circuit is used at the receiver to return the frequency response to normal. ● It's a simple low-pass filter with the same time constant (75 μs) as the pre-emphasis circuit. ● This results in a cutoff frequency of 2123 Hz for the de-emphasis circuit. ● Frequencies above this cutoff are attenuated at 6 dB per octave. ● The de-emphasis effectively cancels out the pre-emphasis, providing a flat frequency response overall.
- 19. Preemphasis De-emphasis at transmitter ● A de-emphasis circuit is used at the receiver to return the frequency response to normal. ● It's a simple low-pass filter with the same time constant (75 μs) as the pre-emphasis circuit. ● This results in a cutoff frequency of 2123 Hz for the de-emphasis circuit. ● Frequencies above this cutoff are attenuated at 6 dB per octave. ● The de-emphasis effectively cancels out the pre-emphasis, providing a flat frequency response overall.
- 20. Preemphasis Overall Effect of Preemphasis and Deemphasis ● The pre-emphasis circuit amplifies high- frequency components of the signal more than low-frequency components, and the de-emphasis circuit attenuates high- frequency components. The ideal outcome is that these opposing effects cancel each other out, resulting in a flat frequency response.
- 22. • Superior Noise Immunity: FM signals are much less susceptible to noise compared to AM signals. This is because FM uses a clipper limiter circuit that removes noise variations, resulting in a constant-amplitude signal. • Capture Effect: In situations with two FM signals on the same frequency, the stronger signal "captures" the channel, eliminating the weaker one entirely. This prevents interference from weaker stations. AM signals, on the other hand, can mix and create an unintelligible mess. • Higher Efficiency: FM transmitters use class C amplifiers which are more efficient than the linear amplifiers required for AM. This allows FM to achieve higher power levels with less wasted energy. Advantages of FM over AM radio
- 23. Excessive Spectrum Usage: • FM signals require a much wider band of frequencies (bandwidth) compared to AM for similar information. This is because FM encodes information by varying the carrier wave's frequency. • Reducing the bandwidth (modulation index) to save spectrum space also reduces FM's key benefit - noise immunity. • FM is typically used at higher frequencies (VHF, UHF, microwave) where wider bandwidth is available. Circuit Complexity (Historical Disadvantage): • In the past, FM equipment required complex circuits for modulation and demodulation compared to simpler AM circuits. • This disadvantage is no longer significant due to the widespread use of integrated circuits (ICs). While FM ICs are intricate, they are affordable and easy to use. Disadvantages of FM over AM radio
- 24. Preemphasis Pre-emphasis and de-emphasis work together to: ● Strengthen high frequencies during transmission. ● Reduce the impact of noise on those frequencies. ● Result in a clearer and more enjoyable listening experience, especially for music.