Analog Communications (SSB) Dr. M. Venu Gopala Rao A.M.I.E.T.E, M.Tech, Ph.D(Engg) Cert. in R.S.T ( City & Guild’s London Institute, London) F.I.E.T.E, L.M.I.S.T.E, I.S.O.I., S.S.I., M.I.A.E. Professor, Dept. of ECE, K L University mvgr03@kluniversity.in

Limitations of AM and DSB-SC Advantages of AM: Receiver design is simplified Dis-advantages of AM: 1. Wastage of Carrier power 2. Wastage of Band width Advantages of DSB-SC : Transmission efficiency improved. Carrier power is suppressed. Dis-advantages of DSB-SC : 1. Wastage of Band width

SSB Advantages: More bandwidth efficient than DSB-SC. SSB requires bandwidth equivalent to message signal bandwidth. Carrier power and one sideband power saving. Power saving 83.33% for 100% modulation. Reduced interference of noise, because of low bandwidth.

SSB Disadvantages: Generation and reception is complicated. The SSB transmitter and receiver need to have excellent frequency stability. A slight change in frequency will distort both the transmitted and received signals. Therefore it is needed ideal filters in implementations. Cannot be used signal with DC.

Review of SS

Hilbert Transform

Hilbert Transform (Phase Shifter)

Frequency Response

Inverse Hilbert Transform:

Let a message signal m(t) is band limited to ‘w’ Hz.

Time Domain Description

Single Tone SSB Modulation Let a single tone message single be

Frequency spectrum of single Tone SSB Modulation

SSB Generation (Modulators)

Frequency Discrimination / Filter Method Two Requirements The pass band of the filter should be same as that of the desired sideband. The transition band of the filter should not exceed twice the minimum frequency component present in the baseband signal. Speech Signal 300 Hz to 3.4 kHz

Suppose we use a two stage modulation scheme in which we select first carrier frequency f1=100 kHz and the second one as f2 = 10 MHz. 600 Hz 6 % Direct 10 MHz 0.06 % cannot met 200.6 kHz 2 %

Stage 1: 100 kHz carrier Stage 2: 10M kHz carrier

Phase Discrimination Method

Detection of SSB Signals

Coherent Detection

Phase Discrepancy Assuming the local oscillator signal to be Unwanted component which cannot be removed by filtering This distortion is not usually very serious for voice communi-cation because human ear is relatively very insensitive to phase changes. However in transmission of music or video signals, this distortion may not always acceptable.

Frequency Discrepancy Let the local oscillator is Although is very small compared to the carrier frequency, the value of is not negligible in comparison with the frequency of the base band signal.

Advantages and Disadvantages More bandwidth efficient than DSB-SC. Carrier power and one sideband power saving. Power saving 83.33% for 100% modulation. Reduced interference of noise, because of low bandwidth. Disadvantages: Generation and reception is complicated. The SSB transmitter and receiver need to have excellent frequency stability. It is needed ideal filters in implementations. Cannot be used signal with DC.

Applications SSB used in applications where the power saving and low bandwidth requirements are important. Widely used in point to point communications. Land or Air Mobile Communications, Telemetry, Military, Navigation and Amateur Radio.