1. Comparison between AM and FM.

S.NO AMPLITUDE MODULATION FREQUENCY MODULATION

1. Amplitude of the carrier is varied according to amplitude of modulating signal.

Frequency of the carrier is varied according to amplitude of the modulating signal.

2. AM has poor fidelity due to narrow bandwidth.

Since the bandwidth is large, fidelity is better.

3. Most of the power is in carrier hence less efficient.

All the transmitted power is useful.

4. Noise interference is more. Noise interference is minimum.

5. Adjacent channel interference is present. Adjacent channel interference is avoided.

6. AM broadcast operates in MF and HF range.

FM broadcast operates in VHF and UHF range.

7. In AM only carrier and two sidebands are present.

Infinite numbers of sidebands are present.

8. The transmission equipment is simple. The transmission equipment is complex.

9. Transmitted power varies according to modulation index.

Transmitted power remains constant irrespective of modulation index.

10. Depth of modulation have limitation .It cannot be increased above 1.

Depth of modulation has no limitation. It can be increased by increasing frequency deviation.

2. Comparison between WBFM and NBFM.

S.NO WBFM NBFM

1. Modulation index is greater than 1. Modulation index is less than 1.

2. Frequency deviation = 75 khz. Frequency deviation is 5 khz.

3. Modulating frequency range from 30Hz-15 Khz.

Modulating frequency=3 Khz.

4. Bandwidth is 15 times NBFM. Bandwidth = 2fm.

5. Noise is more suppressed. Less suppressing of noise.

6. Use: Entertainment and broadcasting Use: Mobile communication

3. Difference between FM and PM

S.NO FREQUENCY MODULATION

PHASE MODULATION

1. The maximum frequency deviation depends upon amplitude of modulating voltage.

The maximum phase deviation depends only upon the amplitude of modulating voltage.

2. Frequency of the carrier is modulated by modulating signal.

Phase of the carrier is modulated by modulating signal.

3. Modulation index is increased as modulation frequency is reduced and vice versa.

Modulation index remains same if modulating frequency is changed.

4. Comparison of AM & ASK

SI.NO PARAMETER AM ASK

1. Nature of modulating signal. Modulating signal is analog.

Modulating signal is digital.

2. Variation in the carrier amplitude.

Carrier variation is according to the amplitude of modulating signal.

Carrier ON or OFF depends on 1 or 0 is to be transmitted.

3. Bandwidth 2fm (1+r)R

4. Noise immunity Poor Poor

5. Application Radio broadcasting Data transmission at low bit rate.

6. Variable characteristics of the carrier.

Amplitude Amplitude

7. Detection method Envelope Envelope

8. Number of sidebands produced Two Two

5. Comparison of Digital Modulation Systems

SI.NO PARAMETER BINARY ASK

BINARY FSK

BINARY PSK

1. Variable Characteristic Amplitude Frequency Phase

2. Noise Immunity Low High High3. Error Probability High Low Low

4. Complexity Simple Moderately complex

High complexity

5. Detection method Envelope Envelope Coherent

6. Bit rate Suitable upto 100 bits/sec

Suitable upto 1200 bits/sec

Suitable higher than 1800 bits/sec

7. Performance in presence of noise.

Poor Better than ASK

Better than FSK

6. Comparison of BPSK and DPSK

SI.NO Parameters BPSK DPSK1. Variable characteristics Phase Phase

2. Error probability Low Higher than BPSK

3. Complexity Lower than DPSK Higher than BPSk

4. Bandwidth fb fb

5. Necessity of synchronization carrier

Necessary Not Necessary

6. Detection method Synchronous Synchronous

7. Noise immunity Low Higher than BPSK

8. Bit determination at the receiver. Based on single bit interval

Based on signal received in two successive bit intervals.

7. Comparison of BPSK and QPSK

SI.NO Parameters BPSK QPSK

1. Type of modulation Two level Four level

2. Bit rate Bit rate = baud rate Bit rate = 2 baud rate

3. Complexity Complex Very complex

4. Noise immunity Same as QPSK Same as BPSK

5. Bandwidth utilization Low when compared to QPSK

Better than BPSK

6. Variable characteristics of the carrier

Phase Phase

7. Applications High speed applications

Very high speed applications.

8. Comparison of QAM and QPSK

SI.NO Parameter QPSK QAM

1. Type of modulation Quadrature phase modulation

Quadrature amplitude and phase modulation.

2. Noise immunity Better than QASK Poorer than QPSK

3. Probability of error Less than QASK More than QPSK

4. Type of Demodulation Synchronous Synchronous

5. Complexity Less complex than QASK

More complex than QPSK

9. Comparison of PAM, PWM and PPM Systems

SI.NO Parameter PAM PWM PPM

1. Variable characteristic of the pulsed carrier

Amplitude Width Position

2. Bandwidth requirement Low High High

3. Noise immunity Low High High

4. Information is contained in.

Amplitude variations

Width variations

Position variation

5. Necessary of synchronization pulses.

Not necessary Not necessary Necessary

6. Complexity in detection and generation

High Low High

7. Transmitted power Varies with amplitude of pulses

Varies with variation in width

Constant

8. Similarly with other modulation system

AM FM PM

10. Comparison of FDMA,TDMA and CDMA.

SI.NO FDMA TDMA CDMA1. Bandwidth sharing among many

users.Time sharing among many users.

Sharing of bandwidth and time both takes place

2. Synchronization is not necessary. Synchronization is essential.

Synchronization is not necessary.

3. Code word is not used. Code word is not used.

Code words are used.

4. No soft capacity limit. No soft capacity limit.

Soft capacity limit is there.

5. No frequency reuse Frequency reuse is used.

Frequency reuse is efficiently implemented.

6. It has higher cell size system cost. Low cell site system cost when compared to FDMA.

Low cell site cost when compared to other systems.

7. Guard bands between adjacent channels are necessary.

Guard times between adjacent time slots are necessary.

Guard bands and times both are necessary.

8. Continuous transmission scheme. Discontinuous transmission scheme.

Both continuous and discontinuous transmission scheme.