SSB Modulator and Demodulator Operating Manual Ver.1.1 An ISO 9001 : 2000 company 94-101, Electronic Complex Pardesipura, Indore- 452010, India Tel : 91-731- 2570301/02, 4211100 Fax: 91-731- 2555643 e mail : info@scientech.bz Website : www.scientech.bz Toll free : 1800-103-5050
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SSB Modulator & Demodulator AB102 Table of Contents 1. Introduction 4 2. Theory 6 3. Experiments Experiment 1 9 To study single sideband AM modulation Experiment 2 11 To study single sideband AM demodulation 4. Warranty 13 5. List of Accessories 13 RoHS Compliance Scientech Products are RoHS Complied. RoHS Directive concerns with the restrictive use of Hazardous substances (Pb, Cd, Cr, Hg, Br compounds) in electric and electronic equipments. Scientech products are Lead Free and Environment Friendly. It is mandatory that service engineers use lead free solder wire and use the soldering irons upto (25 W) that reach a temperature of 450 C at the tip as the melting temperature of the unleaded solder is higher than the leaded solder. Scientech Technologies Pvt. Ltd. 3
Introduction AB102 is a compact, ready to use SSB Modulator & Demodulator Experiment board. This is useful for students to understand functionality of single sideband modulation and demodulation. It can be used with SCIENTECH Analog Lab ST2612 which has built in DC power supply, AC power supply, function generator, modulation generator, continuity tester, toggle switches, and potentiometer. List of Boards : Model Name AB01 Diode characteristics (Si, Zener, LED) AB02 Transistor characteristics (CB NPN) AB03 Transistor characteristics (CB PNP) AB04 Transistor characteristics (CE NPN) AB05 Transistor characteristics (CE PNP) AB06 Transistor characteristics (CC NPN) AB07 Transistor characteristics (CC PNP) AB08 FET characteristics AB09 Rectifier Circuits AB10 Wheatstone Bridge AB11 Maxwell s Bridge AB12 De Sauty s Bridge AB13 Schering Bridge AB15 Common Emitter Amplifier AB14 Darlington Pair AB16 Common Collector Amplifier AB17 Common Base Amplifier AB18 Cascode Amplifier AB19 RC-Coupled Amplifier AB20 Direct Coupled Amplifier AB21 Class A Amplifier AB22 Class B Amplifier (push pull emitter follower) AB23 Class C Tuned Amplifier AB25 Phase Locked Loop (FM Demodulator & Frequency Divider / Multiplier) AB28 Multivibrator ( Mono stable / Astable) AB29 F-V and V-F Converter AB30 V-I and I-V Converter AB31 Zener Voltage Regulator AB32 Transistor Series Voltage Regulator AB33 Transistor Shunt Voltage Regulator AB35 DC Ammeter AB39 Instrumentation Amplifier AB41 Differential Amplifier (Transistorized) AB42 Operational Amplifier (Inverting / Non-inverting / Differentiator) Scientech Technologies Pvt. Ltd. 4
AB43 AB44 AB45 AB49 AB51 AB52 AB54 AB56 AB57 AB58 AB59 AB64 AB65 AB66 AB67 AB68 AB80 AB82 AB83 AB84 AB85 AB88 AB89 AB90 AB91 AB92 AB93 AB96 AB97 AB101 AB106 Operational Amplifier (Adder/Scalar) Operational Amplifier (Integrator/ Differentiator) Schmitt Trigger and Comparator K Derived Filter Active filters (Low Pass and High Pass) Active Band Pass Filter Tschebyscheff Filter Fiber Optic Analog Link Owen s Bridge Anderson s Bridge Maxwell s Inductance Bridge RC Coupled Amplifier with Feedback Phase Shift Oscillator Wien Bridge Oscillators Colpitt Oscillator Hartley Oscillator RLC Series and RLC Parallel Resonance Thevenin s and Maximum power Transfer Theorem Reciprocity and Superposition Theorem Tellegen s Theorem Norton s theorem Diode Clipper Diode Clampers Two port network parameter Optical Transducer (Photovoltaic cell) Optical Transducer (Photoconductive cell/ldr) Optical Transducer (Phototransistor) Temperature Transducer (RTD & IC335) Temperature Transducer (Thermocouple) DSB Modulator and Demodulator FM Modulator and Demodulator and many more Scientech Technologies Pvt. Ltd. 5
Signal Side Band Transmission (SSB) : Theory Single sideband (SSB) AM is a radio communication technique in which the transmitter suppresses one sideband and therefore transmits only a single sideband. Or we can say that it is a refinement of the technique of amplitude modulation designed to be more efficient in its use of electrical power and bandwidth. Amplitude modulation typically produces a modulated output signal that has twice the bandwidth of the modulating signal, with a significant power component at the center carrier frequency. Single sideband modulation improves this.in single sideband; carrier is not transmitted so there is a reduction by 50% of the transmitted power i.e. - 3dBm. Because of SSB, only one sideband is transmitted, so there is a further reduction by 50% in transmitted power i.e. -3dBm (+) -3dBm = -6dBm. Finally, because only one sideband is received, the receiver s bandwidth is reduced by one half. Thus effectively reducing the required power by the Modulator is- 50% (-3dBm (+) -3dBm (+) -3dBm = -9dBm). If a demodulator bandwidth can be reduced by 50%: the needed transmitter power is also reduced by 50%, i.e., the demodulator Signal to Noise Ratio (SNR) is improved as the demodulator bandwidth is reduced. In SSB we transmit only one sideband as shown in figure 1. Figure 1 The bandwidth of an SSB system is equal to the range of frequencies present in the information waveform where as a DSB signal has a bandwidth twice as wide as the highest frequency component in the information signal. This also means a greatly reduced bandwidth for the system. In figures 1 we are transmitting just a single frequency. The SSB Modulator : The design of the SSB modulator is accomplished in two stages. First we generate a DSBSC signal and then remove the lower sideband to achieve the final SSB result. Scientech Technologies Pvt. Ltd. 6
Generating the DSBSC Signal : To do this, we use a balanced modulator. The principle of this circuit is shown in figure 2. Figure 2 Internally, the balanced modulator generates the AM waveform, which includes the carrier and both sidebands. It then offers the facility to feed a variable amount of the carrier back into the modulator in anti-phase to cancel the carrier output. In this way we can balance out the carrier to suppress it completely leaving just the required DSBSC waveform same as shown in fig 3. From DSBSC to SSB : Figure 3 The DSBSC signal consists of the two sidebands, one of which can be removed by passing them through a band pass filter. On the modulator this is achieved as shown in figure 4. Figure 4 Scientech Technologies Pvt. Ltd. 7
The inputs to the balanced modulator comprise the modulating signal, which extend from 300Hz to 3.4 KHz, and the carrier signal of frequency 450KHZ. A ceramic band pass filter (455KHZ) passes only a narrow range of frequencies with a sharp cut-off outside of its pass band. SSB Demodulator : We are using product detector to demodulate the single sideband modulated wave. Product Detector : A product detector is a demodulator which accepts a modulated wave and a carrier wave. The simplest form of product detector multiplies an incoming signal by its carrier with the same frequency and phase as the carrier of the incoming signal. This mixing process results in the generation of two new frequency components. 1. A component whose frequency is the sum of the two input frequencies : 2. A component whose frequency is the difference between the two input frequencies. A low-pass filter at the output of the product detector rejects all frequencies except the difference frequency. Consequently, any slight difference in frequency between the modulator output and carrier frequency will results audio frequency at the product detector's output. Advantages of product detector : 1. The product detector can decode over modulated AM, AM with suppressed carrier, and SSB in addition to regular AM. 2. A signal demodulated with a product detector will have a higher signal to noise ratio than the same signal demodulated with an envelope detector. Scientech Technologies Pvt. Ltd. 8
Objective : Experiment 1 To study Signal Sideband AM Generation. Apparatus required : 1. Analog board AB102. 2. DC power supplies +12V and -12V from external source or ST2612 Analog Lab. 3. Oscilloscope 4. Function generator (ST4063) 5. 2 mm patch cords Circuit diagram : Circuit used to study single sideband modulation is shown in Fig 5. Procedure : Figure 5 Connect +12V and -12V dc power supplies at their indicated position from external source or ST2612 Analog Lab. 1. Apply sine wave of 450KHZ frequency and amplitude 600mV or 0.6Vpp approx at carrier signal socket. This is the carrier input to our balanced modulator. Check the carrier signal frequency (450KHZ) by frequency counter. Scientech Technologies Pvt. Ltd. 9
2. Apply sine wave of frequency ranging to 300 Hz to 3.4 KHz and amplitude 2V pp approx to modulating signal socket. This is the audio frequency sine wave, which will be as our modulating signal. 3. Monitor, in turn, the two inputs to the balanced modulator block, at tp1 and tp2. 4. Next, examine the output of the balanced modulator block at tp3. 5. Turn the balance pot P1, on the board. It is this block that we will use to perform double-side band amplitude modulation. Check that the waveform at tp3 as shown in fig 6. Figure 6 Note that it may be necessary to adjust the balanced modulator block's balance pot, in order to ensure that the peaks of TP.3 waveform envelope (labeled A, B, C etc. in the above diagram) all have equal amplitude. 6. The DSBSC output from the balanced modulator block is next passed on to the ceramic filter block. Observe the output of the ceramic band pass filter block at tp4 together with the audio modulating signal at TP.2. Note that the envelope of the signal at TP. 4 now has fairly constant amplitude, as shown in figure 7. Figure 7 7. Next, vary the amplitude (0V to 2.4V) and frequency (300HZ to 3.4KHZ) of modulating signal throughout its range, and observe the output at tp 4. Observe this change also on frequency counter. This highlights one of the main advantages of SSB amplitude modulation if there is no modulating signal, and then the amplitude of the SSB waveform drops to zero, so that no power is wasted. 8. Return the amplitude pot to its original position. Scientech Technologies Pvt. Ltd. 10
Objective : Experiment 2 To study Single Sideband AM Reception. Apparatus required : 1. Analog board AB102. 2. DC power supplies +12V and -12V from external source or ST2612 Analog Lab. 3. Oscilloscope 4. Function generator (ST4063) 5. 2 mm patch cords Circuit diagram : Circuit used to investigate demodulation of the single sideband amplitude modulated waveform is shown in Fig 8. Figure 8 Scientech Technologies Pvt. Ltd. 11
Procedure : Connect +12V and -12V dc power supplies at their indicated position from external source or ST2612 Analog Lab. 1. Examine the Modulator output signal at TP 4, is a SSB waveform, by checking that the signal is a reasonably good sine wave. 2. Apply carrier signal to the product detector block by connecting 2 mm patch between carrier signal of modulator and demodulator block. 3. Connect 2 mm patch cord between SSB output and SSB Input socket. 4. Monitor, in turn the two inputs of product detector block, at tp5 and tp6. 5. Set 3.4KHZ modulating frequency by function generator. 6. Next, examine the output of product detector block, at SSB demodulated output socket. 7. Vary the amplitude of output wave by varying potentiometer P2 and P3. Potentiometer P2 is used to set magnitude of carrier wave and potentiometer P3 is used to set magnitude of SSB wave. Now, vary the amplitude (0V to 2.4V) and frequency (300HZ to 3.4KHZ) of modulating signal throughout its range, and observe the output at tp7. Note that the frequency of the modulating signal changes, the output from the product detector should follow it. Scientech Technologies Pvt. Ltd. 12
Warranty 1. We guarantee the product against all manufacturing defects for 24 months from the date of sale by us or through our dealers. Consumables like dry cell etc. are not covered under warranty. 2. The guarantee will become void, if a) The product is not operated as per the instruction given in the operating manual. b) The agreed payment terms and other conditions of sale are not followed. c) The customer resells the instrument to another party. d) Any attempt is made to service and modify the instrument. 3. The non-working of the product is to be communicated to us immediately giving full details of the complaints and defects noticed specifically mentioning the type, serial number of the product and date of purchase etc. 4. The repair work will be carried out, provided the product is dispatched securely packed and insured. The transportation charges shall be borne by the customer. For any Technical Problem Please Contact us at service@scientech.bz List of Accessories 1. 2mm Patch cord (Red) 16...2 Nos. 2. 2mm Patch cord (Black) 16...4 Nos. 3. 2mm Patch cord (Blue) 16...5 Nos. 4. E-manual...1 No. Updated 26-06-2009 Scientech Technologies Pvt. Ltd. 13