PASSIVE ATTENUATORS Analog Lab Experiment Board Ver. 1.0 QUALITY POLICY To be a Global Provider of Innovative and Affordable Electronic Equipments for Technology Training by enhancing Customer Satisfaction based on Research, Modern manufacturing techniques and continuous improvement in Quality of the products and Services with active participation of employees. An ISO 9001: 2000 company 94-101, Electronic Complex, Pardesipura INDORE-452010, India. Tel.: 91-731-2570301 Fax: 91-731-2555643
Email: info@scientech.bz Web: www.scientech.bz Scientech Technologies Pvt. Ltd. 2
Scientech Technologies Pvt. Ltd. 3
Scientech Technologies Pvt. Ltd. 4
PASSIVE ATTENUATORS AB50 TABLE OF CONTENTS 1.Introduction 4 2. Theory 6 3.Experiments a. Experiment 1 To study the response of Passive T-Attenuator. 12 b. Experiment 2 To study the response of Passive п -Attenuator. 15 c. Experiment 3 To study the response of Passive Bridge T - Attenuator 18 4.Warranty 21 5.List of Service Centers 22 6.List of Accessories with AB50 23 7. Notes 24 Scientech Technologies Pvt. Ltd. 5
INTRODUCTION AB50 is a compact, ready to use PASSIVE ATTENUATORS experiment board. It incorporates T Attenuator pad, п Attenuator pad and Bridge-T Attenuator pad on a single board and illustrates the functionality of passive attenuator at different attenuation ratio. It can be used as stand alone unit with function generator ST4060 and Oscilloscope. List of boards : Model AB01 AB02 AB03 AB04 AB05 AB06 AB07 AB08 AB09 AB10 AB11 AB12 AB13 AB14 AB15 AB16 AB17 AB18 AB19 AB20 AB21 AB22 AB23 AB25 AB28 AB29 AB30 AB31 AB32 Name Diode characteristics (Si, Zener, LED) Transistor characteristics (CB NPN) Transistor characteristics (CB PNP) Transistor characteristics (CE NPN) Transistor characteristics (CE PNP) Transistor characteristics (CC NPN) Transistor characteristics (CC PNP) FET characteristics Rectifier Circuits Wheatstone Bridge Maxwell s Bridge De Sauty s Bridge Schering Bridge Darlington Pair Common Emitter Amplifier Common Collector Amplifier Common Base Amplifier Cascade Amplifier RC-Coupled Amplifier Direct Coupled Amplifier Class A Amplifier Class B Amplifier (push pull emitter follower) Class C Tuned Amplifier Phase Locked Loop (FM Demodulator & Frequency Divider / Multiplier) Multivibrator ( Mono stable / Astable) F-V and V-F Converter V-I and I-V Converter Zener Voltage Regulator Transistor Series Voltage Regulator Scientech Technologies Pvt. Ltd. 6
AB33 Transistor Shunt Voltage Regulator AB39 Instrumentation Amplifier AB41 Differential Amplifier (Transistorized) AB42 Operational Amplifier (Inverting / Non-inverting / Differentiator) AB43 Operational Amplifier (Adder/Scalar) AB44 Operational Amplifier (Integrator/ Differentiator) AB45 Schmitt Trigger and Comparator AB51 Active filters (Low Pass and High Pass) AB52 Active Band Pass Filter AB53 Notch Filter AB54 Tschebyscheff Filter AB56 Fiber Optic Analog Link AB64 RC Coupled Amplifier with Feedback AB65 Phase Shift Oscillator AB66 Wien Bridge Oscillators AB67 Colpitt Oscillator AB68 Hartley Oscillator AB80 RLC Series and RLC Parallel Resonance AB81 Kirchoff s Laws (Kirchoff s Current Law & Kirchoff s Voltage Law) AB82 Thevenin s and Maximum power Transfer Theorem AB83 Reciprocity and Superposition Theorem AB84 Tellegen s Theorem AB85 Norton s theorem AB88 Diode Clipper AB89 Diode Clampers AB90 Two port network parameter AB91 Optical Transducer (Photovoltaic cell) AB92 Optical Transducer (Photoconductive cell/ldr) AB93 Optical Transducer (Phototransistor) AB96 Temperature Transducer (RTD & IC335) AB97 Temperature Transducer (Thermocouple) AB101 DSB Modulator and Demodulator AB102 SSB Modulator and Demodulator AB106 FM Modulator and Demodulator and many more Scientech Technologies Pvt. Ltd. 7
THEORY A Passive Attenuator is a resistive network that is used to introduce a fixed amount of attenuation between source and load, this device creates loss (attenuation) in transmission line. Attenuator reduces or lowers the amplitude or power of the signal without distorting its waveform. Fixed attenuators are often called pads, especially in telephony. Attenuator pads can be designed with many different attributes: matched impedances, unmatched impedances. The amount of power reduction produced by attenuator is measured in decibels while its overall ability depends on the type of attenuator is being used. The concept is that maximum power transfer occurs when the load impedance matches the source impedance. Today, most audio systems operate on the voltage transmission model. Sources have low impedances, and loads are many times this impedance so that total voltage can transfer. Attenuator can model the connection of source and load as a voltage divider, so that majority of the source voltage appears across the load, and only a small fraction is lost in the resistance representing the source impedance. Any application that requires a reduction in power output may require the installation of attenuators. Passive Attenuator pads are used in amplifier, detectors, match circuits, laboratory application and balance transmission lines. Fig.1 shows the network with and without attenuator. Network (a) without attenuator pad (b) with attenuator pad Fig. 1 Scientech Technologies Pvt. Ltd. 8
In addition to providing attenuation of the signal, the pad usually provide input and output matching, hence R IN must be equal to the source resistance R S and output resistance R OUT must be equal to load resistance R L. If the reference loads current of the network without attenuator is I LO, I LO = E / (R S + R L ) and I L is the reference load current of the attenuation pad (the value of I L is depend on the total resistance of network, which differs according to the resistance arrangement in the network), then the insertion loss (IL) or attenuation due to attenuator pad is, IL = I L / I LO (1) The insertion loss IL is usually quoted in decibels. This will denote by IL db, which by definition is IL db = -20 log [I L / I LO ] (2) The negative sign is to show that attenuation occurs and the insertion loss will be come out as a positive number of decibels. Passive Attenuator has been classified according to the arrangement of resistor in network. Commonly employed attenuator networks are : 1. T attenuator, 2. п attenuator, 3. Bridge-T attenuator. T Attenuator : The name T-attenuator arises due to circuit configured like the letter T of English and is consist of one resistance in each arm. Fig.2 shows the passive T attenuator s circuit diagram. T-attenuator Fig. 2 Scientech Technologies Pvt. Ltd. 9
Applying the Kirchhoff s voltage law to loop consisting of source and R 1 and R 2. Applying the Kirchhoff s voltage law to loop consisting of R 2, R L and R 3. Thus, Put the value of I L in Eq.1 for insertion loss. Thus, For the value of input resistance, the source is removed and the load left connected. The input resistance is that seen looking to the right into the network. For the output resistance, the load is removed and the source left connected (with source emf. at zero). The output resistance is that seen looking to the left into the network. It causes problem in designing an attenuator to meet specified values of input resistance, output resistance and insertion loss. Above equations can be solved for R 1, R 2 and R 3 but to obtain this resistor s value a complex numerical method is to be employed. Furthermore, not all the combinations of input resistance, output resistance met in given attenuation design, and where the design fails, some of the resistor value come out negative; which shows that the attenuator is physically unrealizable. Scientech Technologies Pvt. Ltd. 10
Although the attenuator design is best achieved by computational methods, but when an attenuator has to provide a specific attenuation between a matched source and load, an analytical solution can be used. If, R IN = R OUT = R O and, R 1 = R 2 = R, Then, п-attenuator : The name п-attenuator is arises due to circuit configured like the Greek letter п. Fig.3 shows the п-attenuator. п-attenuator Fig. 3 The input resistance output resistance and insertion loss can be solved in terms of network resistor. Though, the equation can be easily solved in terms of conduction (reciprocal of resistance). Alternatively, these equations transformed through duality to give, for the п-attenuator. Although the equations are most easily solved in terms of conduction, resistor values will usually be specified. Scientech Technologies Pvt. Ltd. 11
The computations therefore require extra steps of converting source resistance and load resistance into conductance and, once the network conduction is found, converting these back into resistor values. Alternatively, a T-attenuator can be design for given insertion loss and value of R 1, R 2 and R 3 can be converted in to R A, R B and R C by using Y- transformation. For the specific case of equal input and output resistance, these equations can be simplified. Where, R A = R B = R, Then, R IN = R OUT = R O Scientech Technologies Pvt. Ltd. 12
Bridge T-Attenuator : The Bridge-T attenuator consists of two networks into one attenuator. It is a very useful tool to reduce the level of a signal without changing the impedance of the circuit. Fig.4 shows the Bridge-T diagram. I2 E Bridge-T Attenuator Fig. 4 Taking the condition when load impedance matches the source impedance, and input resistance is equal to output resistance. The value of R 2 and R 3 is equal to the input output load Then, and, where, R 2 = R 3 = R IN = R OUT = R O IL = log -1 [IL db /-20] R 1 = R 3.(N-1) R 4 = R 3 /(N-1) N = log -1 [IL db /20] Thus N can be define as voltage ratio of attenuator. There is no particular advantage of T-Attenuator over п-attenuator or over Bridge-T Attenuator or vice versa, except then when one type is more practical then another i.e. resistance in one network are more physiable then resistance in another network. Scientech Technologies Pvt. Ltd. 13
EXPERIMENT 1 Objective : To study the attenuation response of Passive T-Attenuator. Apparatus required : 1. Analog board of AB50. 2. Function generator ST4060 3. Oscilloscope 4. Digital Multimeter 5. 2 mm patch cords. Circuit diagram : Circuit used to study the response of Passive Attenuators is in Fig 5. Fig. 5 Scientech Technologies Pvt. Ltd. 14
Procedure : Calculate the value of R 2, R 3 and R 4 for 2db attenuation (insertion loss) by equation given below. 1. Adjust the potentiometer R 2, R 3 and R 4 to set the value of resistance according the calculation. 2. Connect function generator ST4060 probes at socket p and ground for T-Attenuator. 3. Set the 1V pp, 1 KHz input sinusoidal signal of function generator and observe the input at oscilloscope CH II. 4. Observe the output waveform between output socket q and ground, on oscilloscope CH I. 5. Measure the amplitude loss on oscilloscope. 6. Increase the input voltage and measure the amplitude loss for each input voltage. 7. Calculate the value of R 2, R 3 and R 4 for 7db attenuation loss by equation given below. 8. Repeat the above step from 1 to 6. 9. Calculate the value of R 2, R 3 and R 4 for 10db attenuation by equation given below. 10. Repeat the above step from 1 to 6. Note : Any specific value of attenuation (insertion loss) can be taken instead of given values. Scientech Technologies Pvt. Ltd. 15
OBSERVATION TABLE S. No. Attenuation IL db (db) IL R 2 R 3 R 4 Input Output (calculated) Output (measured) Calculation : Measure the value of IL for a given value of IL db, IL db = IL = log -1 [IL db /-20] For a condition where input resistance is equal to output resistance If R IN = R OUT = R O = 50Ω and, R 2 = R 3 = R Then, Result : The measured output of T-Attenuator is. Scientech Technologies Pvt. Ltd. 16
EXPERIMENT 2 Objective : To study the attenuation response of Passive Π-Attenuator. Apparatus required : 1. Analog board of AB50. 2. Function generator ST4060 3. Oscilloscope 4. Digital Multimeter 5. 2 mm patch cords. Circuit diagram : Circuit used to study the response of Passive Attenuators is in fig 6. Fig. 6 Scientech Technologies Pvt. Ltd. 17
Procedure : Calculate the value of R 1, R 2 and R 3 for 2db attenuation (insertion loss) by equation given below. 1. Adjust the potentiometer R 1, R 2 and R 3 to set the value of resistance according the calculation. 2. Connect 2mm patch cord between socket b and p and between socket c and q. 3. Connect 2mm patch cord between socket r and ground, to form a п-attenuator. 4. Connect function generator ST4060 probes at socket a and ground, for п-attenuator. 5. Set the 1V pp, 1 KHz input sinusoidal signal of function generator and observe the input at oscilloscope CH II. 6. Observe the output waveform between output socket d and ground, on oscilloscope CH I. 7. Measure the amplitude loss on oscilloscope. 8. Increase the input voltage and measure the amplitude loss for each input voltage. 9. Calculate the value of R 1, R 2 and R 3 for 7db attenuation loss by equation given below. 10. Repeat the above step from 1 to 8. 11. Calculate the value of R 1, R 2 and R 3 for 10db attenuation by equation given below. 12. Repeat the above step from 1 to 8. Note : Any specific value of attenuation (insertion loss) can be taken instead of given values. Scientech Technologies Pvt. Ltd. 18
OBSERVATION TABLE S. No. Attenuation (db) IL R 1 R 2 R 3 Input Output (calculated) Output (measured) Calculation : Measure the value of IL for a given value of IL db, IL db = IL = log -1 [IL db /-20] For a condition where input resistance is equal to output resistance If R IN = R OUT = R O = 50Ω and, R 2 = R 3 = R Then, Result : The measured output of п-attenuator is. Scientech Technologies Pvt. Ltd. 19
EXPERIMENT 3 Objective : To study the attenuation response of Passive Bridge-T Attenuator. Apparatus required : 1. Analog board of AB50. 2. Function generator ST4060 3. Oscilloscope 4. Digital Multimeter 5. 2 mm patch cords. Circuit diagram : Circuit used to study the response of Passive Attenuators is in Fig 7. Fig. 7 Scientech Technologies Pvt. Ltd. 20
Procedure : Calculate the value of R 1, R 2, R 3 and R 4 for 2db attenuation (insertion loss) by equation given below. 1. Adjust the potentiometer R 1, R 2, R 3 and R 4 to set the value of resistance according the calculation. 2. Connect 2mm patch cord between socket b and p and between socket c and q. 3. Connect function generator ST4060 probes at socket a and ground for Bridge-T Attenuator. 4. Set the 1V pp, 1 KHz input sinusoidal signal of function generator and observe the input at oscilloscope CH II 5. Observe the output waveform between output socket d and ground, on oscilloscope CH I. 6. Measure the amplitude loss on oscilloscope. 7. Increase the input voltage and measure the amplitude loss for each input voltage. 8. Calculate the value of R 1, R 2, R 3 and R 4 for 7db attenuation loss by equation given below. 9. Repeat the above step from 1 to 7. 10. Calculate the value of R 1, R 2, R 3 and R 4 for 10db attenuation by equation given below. 11. Repeat the above step from 1 to 7. Note : Any specific value of attenuation (insertion loss) can be taken instead of given values. Scientech Technologies Pvt. Ltd. 21
OBSERVATION TABLE S. No. Attenuation (db) IL R 1 R 3 & R 2 R 4 Input Output (calculated) Output (measured) Calculation : Measure the value of IL for a given value of IL db, IL db = IL = log -1 [IL db /-20] For a condition where input resistance is equal to output resistance If R IN = R OUT = R O = 50Ω For a Bridge-T Attenuator the value of R 2 and R 3 is also equal to input and output resistor, Then, and, R 2 = R 3 = R O R 1 = R 3.(N-1) R 4 = R 3 /(N-1) where N = log -1 [IL db /20] Thus N can be define as voltage ratio of attenuator. Result : The measured output of Bridge-T Attenuator is. Scientech Technologies Pvt. Ltd. 22
WARRANTY 1. We guarantee the instrument against all manufacturing defects during 24 months from the date of sale by us or through our dealers. 2. The guarantee covers manufacturing defects in respect of indigenous components and material limited to the warranty extended to us by the original manufacturer, and defect will be rectified as far as lies within our control. 3. The guarantee will become INVALID. a. If the instrument is not operated as per instruction given in the instruction manual. b. If the agreed payment terms and other conditions of sale are not followed. c. If the customer resells the instrument to another party. d. Provided no attempt have been made to service and modify the instrument. 4. The non-working of the instrument is to be communicated to us immediately giving full details of the complaints and defects noticed specifically mentioning the type and sr. no. of the instrument, date of purchase etc. 5. The repair work will be carried out, provided the instrument is dispatched securely packed and insured with the railways. To and fro charges will be to the account of the customer. DISPATCH PROCEDURE FOR SERVICE Should it become necessary to send back the instrument to factory please observe the following procedure: 1. Before dispatching the instrument please write to us giving fully details of the fault noticed. 2. After receipt of your letter our repairs dept. will advise you whether it is necessary to send the instrument back to us for repairs or the adjustment is possible in your premises. Dispatch the instrument (only on the receipt of our advice) securely packed in original packing duly insured and freight paid along with accessories and a copy of the details noticed to us at our factory address. Scientech Technologies Pvt. Ltd. 23
LIST OF SERVICE CENTERS 1. Scientech Technologies Pvt. Ltd. 90, Electronic Complex Ph: (0731) 5202959 Pardesipura, Email: info@scientech.bz INDORE 452010 2. Scientech Technologies Pvt. Ltd. Ph.: (011) 26513912, 26864943 First Floor, 14, Uday Park, Fax: (011) 26864943. NEW DELHI 110049 Email: ndel@scientech.bz 3. Scientech Technologies Pvt. Ltd. New no.2, Old no.10, 4 th street Ph.: (044) 42187548, 42187549 Venkateswara nagar, Adyar Fax: (044) 42187549 CHENNAI 600025 Email: chennai@scientech.bz 4. Scientech Technologies Pvt. Ltd. 202/19, 4 th main street Ph.: (080) 51285011 Ganganagar, Fax: (080) 51285022 BANGALORE- 560032 Email: bangalore@scientech.bz 5. Scientech Technologies Pvt. Ltd. Ph.: (022) 56299457 8,1st floor, 123-Hariram Mansion, Fax: (022) 24168767 Dada Saheb Phalke road, Email: stplmum@vsnl.net Dadar (East), MUMBAI 400014 6. Scientech Technologies Pvt. Ltd. 988, Sadashiv Peth, Ph.: (020) 24461673 Gyan Prabodhini Lane, Fax: (020) 24482403 PUNE 411030 Email: pune@scientech.bz 7. Scientech Technologies Pvt. Ltd SPS Apartment, 1 st Floor Ph.: +913355266800 2, Ahmed Mamoji Street, Email: kolkata@scientech.bz Behind Jaiswal Hospital, Liluah, HOWRAH-711204 W.B. 8. Scientech Technologies Pvt. Ltd Ph.: (040) 55465643 Flat No. 205, 2 nd Floor, Email: hyd@scientech.bz Lakshminarayana Apartments C wing, Street No. 17, Himaytnagar, HYDERABAD- 500029 Scientech Technologies Pvt. Ltd. 24
LIST OF ACCESSORIES 1. 2mm Patch cord (Red)... 2 Nos. 2. 2mm Patch cord (Black)... 2 Nos. 3. 2mm Patch cord (Blue)... 3 Nos. Scientech Technologies Pvt. Ltd. 25
NOTES Scientech Technologies Pvt. Ltd. 26