HP 333A User's Manual
Contents
1. 1 3 Distortion levels of 0 1 to 100 full scale are measured in seven ranges for any fundamental frequen cy of 5 Hz to 600 KHz Harmonics are indicated upto 3 MHz The high sensitivity of these instruments re quires only 0 3V rms for the 100 set level reference The distortion characteristics can be monitored atthe OUTPUT connectors with an oscilloscope a true rms voltmeter a wave analyzer The instruments are capable of an isolation voltage of 400 volts above chassis ground 1 4 The voltmeter can be used separately for general purpose voltage and gain measurements It has a frequency range of b Hz to 3 MHz 20 Hz to 500 kHz for 300 uV range and voltage range of 300uV to 300 V rms full scale 1 5 The AM detector included in the Model 334A is a broadband restoring peak detector consisting of semiconductor diode and filter circuit AM distor tion levels as low as 0 3 can be measured on a 3 V to8 V rms carrier modulated 30 in the standard broadcast band Distortion less than 1 can be measured at the same level of the carrier up to 65 Mc Table 1 1 MODEL 333A DISTORTION MEASUREMENT RANGE Any fundamental frequency 5 Hz to 600 kHz Distortion levels of 0 1964 1009 are measured full scale in 7 ranges DISTORTION MEASUREMENT ACCURACY Harmonic measurement accuracy full scale Fundamental Input Less Than 30 V 100 0 3 0 1 1 6 ACCESSORY FEATURES 1 7 The accessory available with th2. OPERATING AND SERVICE MANUAL MODEL 333A 334A DISTORTION ANALYZER Serial Numbers 333A 1137 03146 and greater 334A 1140 05641 and greater Appendix Manual Backdating Changes adapts this manual to lower serial numbers WARNING To help minimize the possibility of electrical fire or shock hazards do not expose this instrument to rain or excess moisture Manual Part No 00333 90008 Microfiche Part No 00333 90058 Copyright Hewlett Packard Company 19 66 P O Box 301 Loveland Colorado 80537 U S A Printed October 1975 HEWLETT PACKARD CERTIFICATION Hewlett Packard Company certifies that this instrument met its published specifications at the time of shipment from the factory Hewlett Packard Company further certifies that its calibration measurements are traceable to the United States National Bureau of Standards to the extent allowed by the Bureau s calibration facility and to the calibration facilities of other International Standards Organization members WARRANTY AND ASSISTANCE This Hewlett Packard product is warranted against defects in materials and workmanship for a period of one year from the date of shipment except that in the case of certain components if any listed in Section I of this operating manual the warranty shall be for the specified period Hewlett Packard will at its option repair or replace products which prove to be defective during the warranty period provided they are r
3. it 4 Observe distortion either in percentage or VOLTAGES LISTED ON REAR PANEL dB as indicated by meter deflection and METER RANGE switch setting For example if meter indicates 0 4 and METER RANGE a Turn instrument on and mechanically zero setting is 1 distortion measured is 0 4 meter according to procedure in Paragraphs of fundamental Similarly if meter indi 3 15 and 3 16 cates 6 dB and METER RANGE setting is 40 dB distortion measured is 46 dB from b Set NORM R F DET switch to R F DET fundamental c Connect input signalto R INPUT terminal on rear panel SUUS d Refer to Paragraph 3 19 for manual distort In MANUAL mode the accuracy ion measurement refer to Paragraph 3 20 of distortion measurements is for automatic distortion measurement affected by frequency stability of the input signal An inaccuracy NOTE in distortion indications occurs when the frequency drift of the If no meter deflection can be input signal exceeds the bandwidth obtained with an RF input diode ACRI should be checked spare diode is located on the outside of the A4 shield of the rejection curve If desired rms voltage of input signal can be measured by setting FUNCTION switch to 3 22 VOLTAGE MEASUREMENT VOLTMETER and setting METER RANGE switch to obtain an on scale indication a Turn instrument on and mechanically zero meteraccordingto procedure in Paragraphs 3 15 and 3 16 3 20 AUTOMATIC MODE
4. meter indication is 10 dB greater than when power dBm measurements are being made 3 26 In short when distortion and voltage measure ments are being made utilizethe instrument METER RANGE and meter scale as they exist For absolute power measurements in dBm simply subtract 10 dB from the METER RANGE setting 3 27 USE OF OUTPUT TERMINALS 3 28 In VOLTMETER and SET LEVEL functions the 333A 334A can be used as a low distortion wide band amplifier portion of the meter input 0 1 V rms open circuit forfullscale meter deflection is provided at the OUTPUT terminals 3 29 In DISTORTION function the distortion 0 1 V rms open circuit forfull scale deflection is provided atthe OUTPUT terminals for monitoring purposes NOTE The INPUT Y terminal and the OUTPUT d terminal shouldnot be connected directly together when making low level measurements These terminals are isolated from each other by 1 ohm which reduces the effects of common mode voltages Model 333A 334 3 30 333A 334A WITH OPTION 01 3 31 Operating procedures for the 333A 334A with OptionOlarethe same asforthe standard instrument The only difference between the standard and optional instrument is that the Option 01 has a special meter and meter amplifier whichis compensated to respond to VU volume unit characteristics 3 32 MANUAL NULLING 3 33 Since the frequency and balance controls are rather sensitive in the MANUAL mode the following
5. Ce d Et Perform steps athroughlof Paragraph 3 19 b Set NORM R F DET switch to NORM i Adjust frequency dial vernier and BALANCE c Set FUNCTION switch to VOLTMETER COARSE and FINE controls for minimum d Set METER RANGE switch to a range meter indication exceeding amplitude of signal to be mea sured When meter indication is less than 10 of SET LEVEL indication set MODE switch to Connect signal to be measured to INPUT AUTOMATIC fundamental cannot be terminals manually nulled below 10 of SET LEVEL indication automatic mode cannot be used f Set METER RANGE switch to give a reading as close to full scale as possible and 00 Set METER RANGE switch down scale to serve meter indication obtain on scale meter indication g The dB scale of the 333A 334A is calibrated Observe distortion either in percentage or in dBm such that 0 dBm 1 milliwatt dissi dB as indicated by meter deflection and pated by 600 ohms Therefore a dBm mea METER RANGE switch setting For example surement must be made across 600 ohms if meter indicates 0 4 and METER RANGE However dB measurements across other setting is 10 distortion measured is 0 4 impedances can be converted to dBm by use of fundamental Similarly if meter indicates of the Impedance Correction Graph of Fig 6 dB and METER RANGE setting is 40 dB ure 3 3 For example to convert a 30 dB distortion measured is 46 dB from funda reading across 200 ohm
6. information is suppliedto simplify nulling the 333A 334A the MANUAL mode When nulling the 3334 3344 in the MANUAL mode connect the equip ment as shown below and adjust the 333A 334A fre quency and balance controls for the waveform shown in step a below Additional waveforms are provided to simplify nulling www No harmonic distortion Frequency and balance adjustment correct b 7 Frequency and balance control im properly adjusted Frequency approximately correct balance incorrect d CLLD Balance approximately correct fre quency incorrect e COX 2 Second harmonie predominant fre quency and balance adjusted f 77 Second harmonie predominant fre quency and balance adjusted phase changed ge 7 Second harmonic predominant fre quency and balance adjusted phase changed CXX Third harmonic predominant i n 2 pee incorrect meter reading off Scale h P AE Frequency incorrect meter reading off scale Model 333 334 TEST OSCILLATOR BISA METER CORRECTION DBM Se Se 2 28 FM vem PPAR ae a RICOTTA NLL mnm ttbi KG rA Figure 8 3 OSCILLOSCOPE DISTORTION ANALYZER hp 3338A 3344 Lir MIN Saat E manent EHI m de Impedance Corr ction Graph Breseseacee Section TIT VES Mod
7. is not con stant Typically the second harmonic is attenuated several dB more than the third harmonic andthethird more than the fourth The result of the negative feed back is illustrated by the rejection characteristic Shown in dashed lines on the attenuation and phase characteristic of Figure 4 3 Figure 4 6 shows a simplified block diagram of the rejection amplifier with the typical frequency rejection characteristic Refer to Figure 4 7 Bandwidth Versus Null Depth for further detail on the rejection characteristic 4 39 HIGH PASS FILTER Refer to Figure 7 3 4 40 The HIGH PASS FILTER is normally used when the fundamental of the input signal is greater than 1 kHz In the voltmeter mode of operation the filter is not used In SET LEVEL and DISTORTION func tions the filter presents 40 dB attenuation to 50 or 60 Hz hum components but offers no attenuation to frequencies over 1 kHz The filter assembly consists of A7C1 2 711 The filter can be inserted or bypassed by the HIGH PASS FILTER switch S9 4 41 METER AMPLIFIER Refer to Figure 7 4 4 42 The meter amplifier consists of the post atten uator the meter amplifier circuit and the meter rectifier circuit 4 43 POST ATTENUATOR 4 44 The post attenuator S3R1 through S3R11 is a resistive network which attenuates the input signal in 10 dB steps The attenuator is usedin conjunction with either the input sensitivity attenuator or the 1
8. of the metering circuit which contains the fundamental frequency if either leg of the bridge is untuned is applied to the buffer amplifier A5Q1 It is amplified by A5Q2 and A5Q3 and coupled to the detector 504 4 30 RefertoFigure 4 4 partial schematic for detector operation The discussion is applicable to both resistive and reactive detector circuits 4 31 The signals from the error amplifier A5Q2 and A5Q3 will be equal and of opposite phase and will cancel out each other when the detector A5Q4 is off However when the positive half of the reference square wave gates A5Q4 on the signal from the coll ector of A5Q3 will be shorted to ground Thus the signal from the collector of A5Q2 will be coupled through the filter network to the base of A5Q5 If the signal from A5Q2 is in phase with the reference the positive half of the signal will be passed and if it is out of phase the negative half will be passed 4 32 The normal working voltage at ASTP3 is be tween 0 1volt The de output of the filter network causes the voltage at ASTP3 to go in a positive direc tion toward zero for in phase error signals and in a negative direction toward 1 V for out of phase error signals The change in base voltage is then amplified by A5Q5 and lamp driver 566 This will change the brilliance of lamp 6051 which will vary the resist ance of A6V1 inthe direction necessary to balance the resistive leg of the bridge COLL
9. the meter circuit in the overall feedback loop 4 49 POWER SUPPLY CIRCUIT Refer to Figure 7 6 4 50 The power supply circuit consists of a 25 volt series regulated supply anda 25 volt series regulated supply which is the reference supply for the 25 volt supply 4 51 The 25 volt regulated supply is ofthe conven tional seriesregulator type The amplifier A1Q5 is used to increase the loop gain of the circuit thus im proving voltage regulation The positive feedback applied to the junction of A1R11 and A1R12 is used to further improve the line frequency suppression of the circuit 4 52 The 25 volt regulated supply is of the conven tional series regulator type and operates the same as the 25 volt regulated supply 4 53 RF DETECTOR CIRCUIT 334A only Refer to Figure 7 2 4 54 The RF detector circuit consists of a rectifier 1 and filter circuit The RF signal is applied to the circuit through the RF INPUT connector onthe rear panel The rectifier diode A4CR1 recovers the modulating signal from the RF carrier and the fiiter circuit removes any RF components before the signal is applied to the impedance converter circuit through the NORM RF DET switch 87 3334 3344 AO Simplified Metering Circuit 4 7
10. 000 1 attenuator to limit the signal level to the meter amplifier to 1 mV for full scale deflection on all ranges from 1 mV to 300 V full scale The meter circuit sensitivity is increased to 300 for full scale deflection on the 0003V range by switching resistors A2R29 and A2R30 into the calibration net work Resistor A2R41 and capacitor A2C29 are also Switched into the calibration network on the 0003V range to extend the passband of the amplifier 4 45 METER AMPLIFIER CIRCUIT 4 46 The meter amplifier circuit consists of a five stage amplifier circuit A2Q5 through A2Q9 which develops the current for full scale meter deflection Negative dc feedback from the emitter circuit of A2Q8 is applied to the base of 205 to stabilize the dc operating point of the meter amplifier circuit and to minimize the tendency for de drift due to ambient temperature changes A2R51 and A2CR8 are electric ally in the circuit only whenthe meter amplifier is over loaded When the voltage on the emitter of A2Q9 4 5 Section IV Model 333A 334A 00 9095 eS EE 80 poU ay 70 ee 60 A SSE ee LENSES Dei ay DEDERE TEE iets Gad Gite IRR 50 See EE 40 Z SAO EROT TER E 1 eee eee eee eee 30 RENE CINES e NEM EN NEN o RE RSEN See 20 p
11. 2 18 if it is not If you have any questions con tact your local hp Sales and Service Office See Appendix B for office locations NOTE the instrument is to be shipped to Hewlett Packardfor service or repair attachatag to the instrument identify ing the owner and indicate the service orrepairto be accomplished Include the model number and full serial num ber of the instrument In any corres pondence identify the instrument by model number serial number and serial number prefix 2 17 If original container is to be used proceed as follows Place instrument in original container if avail able original container is not available a suitable one can be purchased from your nearest hp Sales and Service Office b Ensurethat container is well sealed with strong or metal bands 2 18 If original container is not to be used proceed as follows a Wrap instrument in heavy paper or plastic be fore placing in an inner container b Place packing material around all sides of in strument and protect panelface with cardboard strips c Place instrument and inner container in a heavy carton or wooden box and seal with strong tape or metal bands d Mark shipping container with DELICATE INSTRUMENT FRAGILE etc 2 1 Section RE DETECTOR MAX INPUT VOLTAGE 40 VOLT P P AC OR 40 VOLT PEAK TRARSENT 333A 2544 C Q3854 j 334A ONLY LINE switch turns instrument
12. ECTOR COLLECTOR OF Q3 OF Q2 6 TP2 RIO RII COLLECTOR CIRCUIT Q9 3334 3344 ROR Auto Control Loop Detector Figure 4 4 4 3 Section IV 4 33 Refer to Figure 4 5 for the phase relationship of the bridge error signal andreference voltage at the base of 594 The shaded portions of the error sig nals b and c indicate that part of the error signal which contributes to the dc lamp control voltage indicatedind any error signal that is 90 out of phase with the reference does not affect the dc lamp control voltage because equal amounts of the positive and negative portions are passed 4 34 The operation of the reactive branch control loop is similar to that of the resistive branch The Ref signalforResistive Detector A5Q4 Resistive Error signal in phase with reference at bridge Resistive Error signal 180 out of phase Reactive Error signal 90 out of phase Results in no output from Re sistive Detector Error signal reactive leg detuned resistive leg unbalanced 333A 334A RO Model 333A 334A phase delay circuit A5Q15 A5Q16 S4AF and S4C1 through S4C5 shifts the reference voltage 909 as shown in Figure 4 5f This makes the detector A5Q12 sensitive to components of the bridge error signal that are 909 out of phase g and h The output of the lamp driver A5Q14 controls the brilliance of A6DS2 which varies the resistance of A6V2 through A6V5 to tun
13. GE switch t SET LEVEL and set BALANCE COARSE and FINE con trols to center position Connect signal to be measuredto 333A 334A INPUT terminals WARNING REMOVE SHORTING STRAP BETWEEN FRAME GROUND 4 AND CHASSIS GROUND TERMINALS ON FRONT PANEL INPUT TERMINALS WHEN MEASURING DISTORTION BETWEEN TWO POINTS WHICH ARE DC OF FSET FROM GROUND POTENTIAL Set SENSITIVITY selector to obtain meter indication greater than 1 3 full scale Adjust SENSITIVITY VERNIER for full scale meter indication if making distortion measure ment in percent if making distortion measure ment in dB adjust SENSITIVITY VERNIER for 0 dB meter indication NOTE If unable to adjust for full scale or 0dB indication which indicates input signal is below 0 3 volts set METER RANGE selector down scale Use this new setting as the 1000 0dB SET LEVEL position thus making the next range 3090 or 10 dB etc Set FREQUENCY RANGE switch and frequency dial to fundamental frequency of input signal Set FUNCTION switch to DISTORTION Adjust frequency dial vernier and BALANCE COARSE and FINE controls for minimum Model 333A 334A Section III n p meter indication Set METERRANGE switch 3 21 DISTORTION MEASUREMENT OF RF down scale as necessary to keep meter in CARRIERS 334A only dication on scale rV Repeat step m until no further reduction in meter indication can be obtained DO NOT EXCEED MAXIMUM INPUT
14. ac power on Pilot lamp glows when instrument is turned ON 2 Meter indicates distortion or voltage level of input 3 switch selects MANUAL or AUTOMATIC bridge tuning operation 4 FREQUENCY RANGE switch selects frequency range which corresponds to fundamental of input signal 5 COARSE BALANCE control provides coarse ad justment for balancing the Wien bridge circuit 6 FINE BALANCE control provides a vernier ad justment for balancing the Wien bridge circuit 1 Frequency dial tunes the Wien bridge circuit to fundamental of input signal 8 HIGH PASS FILTER switch inserts or bypasses HIGH PASS FILTER in SET LEVEL and DIS TORTION function When inserted filter pro vides gt 40 dB attenuation to 50 60 Hz hum components but no attenuation to frequencies over 1 kHz OUTPUT connectors provide means of monitor ing output of meter circuit 10 Frequency vernier provides fine adjustment of frequency dial METER RANGE switch selects full scale range of meter in percent dB and rms volts Model 333A 334A METERS JANGE 547 LEVES CAUTION 12 sENSITIVITY selector provides 0 50 dB attenu ation of input signal in 10 dB steps in SET LEVEL and DISTORTION functions IS SENSITIVITY VERNIER control provides fine adjustment of sensitivity setting Mechanical zero adjust provides mechanical zero adjustment of meter FUNCTION switch selects type of operation of instrument 16 short
15. dB 20 Hz to 20 kHz better than 0 6 dB 20 kHz to 100 kHz better than 1 dB 100 kHz to 300 kHz better than 2 dB 300 kHz to 600 kHz better than 3 dB 1 1 Section I Model 333A 334A Table 1 1 Specifications Cont d Distortion Introduced by Instrument gt 70 from 5 Hz to 200 kHz gt 64 dB from 200 kHz to 600 kHz Meter indication is proportional to the aver age value of a waveform FREQUENCY CALIBRATION ACCURACY Better than 5 from 5 Hz to 300 kHz Better than 1096 from 300 kHz to 600 kHz INPUT IMPEDANCE Distortion Mode 1 5 shunted by 70 pF Voltmeter Mode 1 5 shunted by 30 pF 333A only 1 MQ 5 shunted by 35 pF 334A only 1 to 300 V ranges 1 5 shunted by 70 pF 300 u V to 0 3 V ranges INPUT LEVEL FOR DISTORTION MEASUREMENTS 0 3 V rms for 100 set level up to 300 V may be attenuated to set level reference The minimum measurable distortion for floating operation on the X1 frequency range is 50dB below the fundamental DC ISOLATION Signal ground may be 400 Vdc from external chassis VOLTMETER RANGE 300 to 300 V rms full scale 13 ranges 10 dB per range VOLTMETER FREQUENCY RANGE 5 Hz to 3 MHz 300 uV range 20 Hz 500 kHz VOLTMETER ACCURACY 20 Hz 500 kHz 5 Hz 3 MHz 5 Hz 500 kHz 30 Hz 300 kHz lmV 30V 1 10 Hz i MHz 100 V 300 V 10 Hz 300 kHz 300 MODEL 334A Same as Model 333A except as indicated below AM DETECTOR High im
16. e 333A and334A Distortion Analyzers is a voltage divider probe hp Model 10001A The features of the probe are a 10 megohms shunted by 10 pF giving 10 1 attenuation b DC to 30 MHz bandwidth 2 division accuracy d 600 V peak input e 5 ns rise time 1 8 OPTION 1 9 Option 01 standard hp Model 333A or 334A with a special meter and meter amplifier compen sated to permit response to VU volume units characteristics 1 10 INSTRUMENT IDENTICATION 1 11 Hewlett Packard uses a two section serial number The first section prefix identifies a series of instruments The last section suffix identifies a particular instrument within the series letter is included with the serial number it identifies the coun try in which the instrument was manufactured the Serial prefix of your instrument differs from the one on the title page of this manual a change sheet will be supplied to make this manual compatable with new er instruments or the backdating information in dix C will adapt this manual to earlier instruments All correspondence with Hewlett Packard should in clude the complete serial number Specifications Fundamental Input Greater Than 30 V 100 0 3 10 300 30 Hz 300 10 Hz 3 MHz 10 Hz 1 2 MHz 0 1 Elimination Characteristics Fundamental Rejection gt 80 dB Second Harmonic Accuracy for a fundamental of 5 Hz to 20 Hz better than 1
17. e the branches of the reactive leg Deck AR of the FREQUENCY RANGE switch S4 switches 5 56 in parallel with A5R55 on the top three fre quency ranges 6052 willbecome brighter andlower the resistance of A6V2 through A6V5 making variation o 3 5 360 Lr 1 1809 Ref signal for Reactive Detector A5Q12 Reactive Error signal in phase with reference at bridge Reactive Error signal out of phase Resistive Error signal 90 out of phase Results in no output from Re active Detector Error signal Reactive leg detuned Resistive leg unbalanced Figure 4 5 Reference and Error Phase Relationship Model 333A 334A BRIDGE AMPLIFIER 394 A3Q6 WEIN BRIDGE NEGATIVE FEEDBACK 3334 334A RO Section 5 50 500 5000 50K 600K AMPLIFIER GAIN db FREQUENCY Figure 4 6 Rejection Amplifier Block Diagram and Typical Frequency Rejection Characteristic in resistance less than on the two lower ranges How ever less variation in resistance is needed to tune the leg because the impedance in the reactive leg becomes progressively less as the higher frequency ranges are selected 4 35 Any error signal that is not an integral multiple of 90 is the result of the reactive leg of the bridge being detuned andthe resistive leg being unbalanced For example an error signal that is 45 out of phase Figure 4 5e and j will resul
18. ee dc Ce FRANK es 0295 eS ee Ep iraq ol vcr Ot SO SE EE EE EE SL CE OA NT ART SARA SUO NENA 008 panman Sissi O ae a ee 007 EA ea TE O eS ae eee ee a Ses 006 BEEN eee ae a ee ee SGA ERGO Ee A ee doe Slo ee ee TL CTE ESET 004 eae Deere BERE i H Aa BAINS NEUEN alqm DRIN qun mmi SC Cpe ERR l a ds pou qp pec esee Lr calescere is a 30 40 50 60 TO Af DEPTH OF NULL DB APPROXIMATE PERCENT BANDWIOTH p X 100 o 333A 334A RO 1 Figure 4 7 Bandwidth Versus Null Depth 4 6 Model 333 334 becomes abnormally large during anoverload A2CR8 breaks down and provides a lower resistance charg ing path for 2 15 which reduces the transient re covery time ofthe meter amplifier Negative ac feed back is applied from the collector circuit of A2Q9 to the emitter circuit of A2Q5 This feedback is used to ensure flat frequency response to improve linear ity and to reduce the effect of variationoftran
19. el 333A 334A Section IV UIBISCIC YOO I p mee tte HA REEO 9 YHES TEES 339 Q3Xxia TVnNVW 130 T aSvHd es dWvi Be ER 39V LIOA EAN Q3xi3 Nas 2 Tw i 70 S 3vnNvw 44 N O SNINAL C E 85 cL a H3l JI dy 602v Sb2v 3901 48 U3IJITdWV 3Hd YILIN i HESS gt gt z UOLT Liv 32v80334 1SOd EN etter strani NOLLO3P 3H 1 ALIALLISN S 9425 4 19 WHO 93W hy ALIALLISNSS AINO Vee 139 NV NOLLYOLSIC O J33A31 138 eiues ziues POZY OZY OO Y3LHJANOD SUI IS O d Ei YSLAWLIOA HIS O d 48 ANON ricco Yen gh E s Nor1oNna 39NVH FILIN 4 0 Model 333A 334A SECTION THEORY OF 4 1 OVERALL DESCRIPTION 4 2 Models 333A and 334A Distortion Analyzers in clude an impedance converter a rejection amplifier a metering circuit and a power supply The Model 334A also contains an AM detector The impedance converter provides a low noise input circuit with a high input impedance independent of source impedance placed at the INPUT terminals The rejection ampli
20. ens DEN E eee ENT ENS DO A a SE SE 9 8 9 6 17 SS e E NN 5 eS DOE SEND AE Se erent oo EE TEREA TA EEN 4 MASE EE RR SE RIS i e Te RT ucro E o d qum D pl E eec 39 Rss HRS ER SEED o LN T MM ROME Ld 2 pt red 1 9 8 7 ST CT MESSEN ENZEILUS CANT RT ESER AT CCA NARS LANL CNA ERT 7 aR ENEMY PSN 6 RR SR ae a semet a INNEN 5 SERE ers aa le oe EAA pee 4 A A a SE ST CAS CT URGE ORCL AACA MEL EN NN 1 Ee 3 COGS PE RM ORME RS CREE as Pe CS VE 2 08 09 pepe ud eI DEPT ae A a ji 07 DE SONSGEEE 106 e eB 05 ee ee ee ee ee eee 04 LE NY TS ey Ree ees ears SE AT S 03 Ae Sees Gee Ge
21. esponding meter is sufficiently close to the rms value to be satisfactory for most applications 3 12 OUTPUT TERMINALS 3 13 The OUTPUT terminals provide a 0 1 V rms open circuit output for full scale meter deflection These terminals can be used to monitor the output signal with an oscilloscope a true rms voltmeter or a wave analyzer The combination of the distortion meter and oscilloscope provides more significant in 3 1 Section formation about the device under test than the expression of distortion magnitude alone Information obtained from the oscilloscope pattern is specific and reveals the nature of distortion which sometimes occurs at such low levels that it is difficult to detect in the presence of hum and noise The impedance at the OUTPUT terminals is 2000 ohms therefore ca pacitive loads greater than 50 pF should be avoided to maintain the accuracy of meter readings 3 14 OPERATING PROCEDURES 3 15 INSTRUMENT TURN ON a Setthe 115 230 VAC switch to coincide with the line voltage in use Turn switch to ON position Pilot lamp willglow indicating application of primary power 3 16 ADJUSTMENT OF METER MECHANICAL ZERO 3 17 The meter is properly zero set when the pointer rests over the zero calibration mark and the instrument is in its normal operating enivronment and is turned off Zero set the meter as follows to obtain maximum accuracy and mechanical stability a Turn instrument on and allow it t
22. eturned to Hewlett Packard and provided the proper preventive maintenance procedures as listed in this manual are followed Repairs necessitated by misuse of the product are not covered by this warranty NO OTHER WARRANTIES ARE EXPRESSED OR IMPLIED INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE HEWLETT PACKARD IS NOT LIABLE FOR CONSEQUENTIAL DAMAGES If this product is sold as part of a Hewlett Packard integrated instrument system the above warranty shall not be applicable and this product shall be covered only by the system warranty Service contracts or customer assistance agreements are available for Hewlett Packard products For any assistance contact your nearest Hewlett Packard Sales and Service Office Addresses are provided at the back of this manual Model 333A 334A Section I SECTION GENERAL INFORMATION 1 1 DESCRIPTION 1 2 The Hewlett Packard Models 333A and 334A Distortion Analyzers are solid state instruments for measuring distortion on ac voltages The Models 333A and 334A include two control loops that auto matically tune both legs of a bridge circuit which re jects the fundamental when the rejection circuit is initially set within the range of the loops The 334A has a high impedance detector which operates from 550 kHz to greater than 65 MHz and provides the ca pability of monitoring the distortion of the amplitude modulation on an rf carrier
23. fier rejects the fundamental frequency of the input signal and passes the remaining frequency components on to the metering circuit for measuring distortion The metering circuit provides visual indications of distortion and voltage levels on the front panel meter M1 The AM detector Model 334A only detects the modulating signal from the RF carrier and filters all RF components from the modulating signal before it is applied to the impedance converter circuit 4 3 BLOCK DIAGRAM DESCRIPTION Refer to Figure 4 1 4 4 DISTORTION MEASURING OPERATION 4 5 For distortion measurement the input signalis applied to the impedance converter Assembly 2 through the FUNCTION selector S1 and the one megohm attenuator The one megohm attenuator is a voltage divider network which provides 50 dB atten uation in 10 dB steps The desired level of attenuation is selected by the SENSITIVITY selector 62 The impedance converter provides impedance matching and unity gain between the INPUT terminals and the input of the rejection amplifier 4 6 Therejectionamplifier consists of a preamplifier a Wien bridge andabridge amplifier The SENSITIVITY VERNIER control at the input of the preamplifier provides a set level signal to obtain a full scale read ing on the meter for any voltage level at the input of the instrument With the FUNCTION switch inthe SET LEVEL position a ground is applied to the Wien bridge circuit to allow a signal reference le
24. he preamplifier A3Q1 thru A3Q3 the Wien bridge resistive leg and auto control loop 501 thru A5Q9 with associated lamp and photocell the reactiveleg and auto control loop A5Q10 thru A5Q18 with associ ated lamp and photocell and the bridge amplifier A3Q4 thru A3Q6 4 19 PREAMPLIFIER CIRCUIT 4 20 The signal from the impedance converter is applied to the preamplifier which is used during SET LEVEL and DISTORTION measuring operations Negative feedback from the junction of 10 and 1 is applied to the junction of A3R2 and to establish the operating point for A3Ql Negative feedback from the emitter of A3Q3 is applied to the emitter of A3Q1 to stabilize the preamplifier The preamplifier like the impedance converter is designed for high open loop gain and low closed loop gain to minimize instrument induced distortion 4 21 WIEN BRIDGE CIRCUIT 4 22 Inthe distortion measuring operationthe Wien bridge circuit is used as a rejection filter for the fundamental frequency of the input signal With the FUNCTION selector S1 inthe DISTORTION position the Wien bridge is connected as an interstage coupling network between the preamplifier circuit and the bridge amplifier circuit The bridge is tuned to the fundamental frequency of the input signal by setting the FREQUENCY RANGE selector S4 for the appli cable frequency range andtuning the capacitors C4A through C4D The bridge circuit is balanced by ad justi
25. iers The input signal is applied to the in put of the AM detector circuit where the modulating signal is recovered from the RF carrier The signal is then applied to the impedance converter circuit through the one megohm attenuator and then through the same circuits previously described in the distor tion measuring mode operation 4 10 VOLTMETER OPERATION 4 11 Inthe voltmeter mode of operation the input signal is applied to the impedance converter circuit through the 1 1 and 1000 1 attenuator The 1 1 atten uation ratio is used onthe 0 0003 100 3 VOLTS ranges and the 1000 1 attenuation ratio is used in the 1 to 300 VOLTS ranges With the FUNCTION switch in the VOLTMETER position the output of the impedance converter bypasses the rejection amplifier and is applied to the metering circuit through the post attenuator METER RANGE switch Metering circuit sensitivity is increased from 1 mV for full scale deflection to 300 u V on the 0003V range as it was in the distortion measuring operation The function of the post attenuator and metering circuit is the same for voltmeter operation as for the distortion measuring operation 4 12 DETAILED CIRCUIT DESCRIPTION 4 13 IMPEDANCE CONVERTER CIRCUIT Refer to Figure 7 2 4 14 The input signal is applied to the impedance converter circuit through the 1 1 and 1000 1 attenuator S3R12 in voltmeter operation and through the one megohm attenuator S2R1 through S2R6 in distorti
26. iers modulated 30 NOTE Distortion measurement at carrier levels as low as i volt may be made with reduced accuracy OPTION 01 Indicating meter has VU characteristics con forming to FCC Requirements for AM FM and TV broadcasting Model 333 334 Section SECTION INSTALLATION 2 1 INTRODUCTION 2 2 This section contains information and instruc tions necessary forthe installation and shipping of the Models 333A 334A Distortion Analyzers Included are initial inspection procedures power and grounding requirements installation information and instruc tions for repackaging for shipment 2 3 INSPECTION 2 4 This instrument was carefully inspected both mechanically and electrically before shipment It shouldbe physically free of mars or scratches and in perfect electrical order upon receipt To confirm this the instrument should be inspected for physical damage intransit Also checkfor supplied accessories and test the electrical performance of the instrument using the procedure outlined in Paragraph 5 5 If there is damage or deficiency see the warranty on the inside front cover of this manual 2 5 POWER REQUIREMENTS 2 6 The Model 333A 334A can be operated from any ac source of 100 V 120 V 220 V 240 V 5 10 48 66 Hz With the instrument disconnected from the ac power source move the slide located on the rear panel until the desired line voltage appears Power dissipation is approxi
27. ing bar connects circuit ground to chassis ground INPUT terminals provide connections for input signal 18 NORM RF DET Model 334A only selects front panel INPUT or rear panel RF INPUT connector 9 RF INPUT connector Model 334A only provides input connection for AM RF carrier input signal FUSE provides current overload protection for instrument circuits 21 Line voltage switch sets instrument to operate from 100 V 120 V 220 V 240 V 22 Ac power connector provides input connection for ac power Figure 3 1 Front and Rear Panel Description 3 0 Model 333A 334A Section SECTION OPERATING 3 1 INTRODUCTION 3 2 The Models 333A and 334A Distortion Analyzers measure total harmonic distortion of fundamental fre quencies from 5 Hz to 600 kHz harmonics upto 3 MHz are included The sharp elimination characteristics gt 80 dB the low level of instrument induced distor tion and the meter accuracy of these instruments re sult in highly accurate measurement of low level har monic distortion 3 3 Anrms calibrated voltmeter is inherent in the 333A and 334A The voltmeter provides a full scale sensitivity of 300 volts rms residual noise 254 volts The voltmeter frequency range is from 5 Hz to 3 MHz except on the 0 0003 volt range which is from 20 Hz to 500 kHz 3 4 CONTROLS AND INDICATORS 8 5 Figure 3 1 illustrates and describes the function of all front and rear panel control
28. mately 4 watts 2 7 THREE CONDUCTOR POWER CABLE 2 8 protect operating personnel the National Electrical Manufacturers Association NEMA recom that the instrument panel and cabinet be grounded Hewlett Packard instruments are equipped with a three conductor power cable which when plugged in toanappropriate receptacle grounds the instrument The offset pin on the power cable three prong connec tor is the ground wire 2 9 INSTALLATION 2 10 The Model 333A 334A is fully transistorized therefore no special cooling is required However the instrument should not be gperated where the am bient temperature exceeds 55 C 131 2 11 BENCH INSTALLATION 2 12 The Model 333A 334A is shipped with plastic feet and tilt stand in place ready for use as a bench instrument 2 13 RACK INSTALLATION 2 14 The Model 333A 334A may be rack mounted by using the 5 RackMount Kit hp Part No 5060 0775 Instructions for the conversion are included with the kit The rack mount for the Model 333A 334A is an EIA standard width of 19 inches When mounted in rack using the rack mount kit additional support at the rear of the instrument should be provided if vibra tion or similar stress is likely 2 15 REPACKAGING FOR SHIPMENT 2 16 The following paragraphs contain a general guide for repackaging of the instrument for shipment Refer to Paragraph 2 17 if the original container is to be used
29. n of the meter indication of a sine wave partly distorted by harmonics in dicated in the table harmonic content of less than 10 results in very small errors INSTRUCTIONS Table 3 1 Effect of Harmonics on Voltage Measurements True Meter RMS Value Indication Fundamental 100 100 Fundamental 10 100 2nd harmonic Fundamental 20 2nd harmonic Fundamental 50 2nd harmonic Fundamental 10 8rd harmonic Input Voltage Characteristics 100 102 100 110 96 104 Fundamental 20 3rd harmonic 94 108 Fundamental 50 3rd harmonic 90 116 l NOTE This chart is universal in application since these errors are inherent in all average responding voltage measuring instruments 3 11 When making distortion measurements where the fundamental frequency is suppressed and the re mainder of the signal is measured the reading ob tained on an average responding meter may deviate irom the true total rms value When the residual wave contains many inharmonically related sinusoids the maximum error in the distortion reading is about 11 11 of the measured distortion low for dis tortion levels below 10 EXAMPLE Measured Maximum Error Total Distortion In Meter Indication Distortion 2 5 0 11x0 025 0 025 0 0027 0 00027 0 0277 or 2 8 This example representsthe maximum possible error and in most cases the error is less In distortion measurements the reading of an average r
30. ng the COARSE balance control R4 andthe FINE balance control R5 In the AUTOMATIC MODE fine tuning and balancing are accomplished by photoelectric cells which are in the resistive and reactive legs of the Wien bridge The error signals for driving the photocells are derived by detecting the bridge output using the input signal as a reference 4 23 When the Wien bridge is not tuned exactly to the frequency tobe nulled a portion of the fundamental 4 2 Model 333A 334A iNPUT TO BRIDGE A OUTPUT OF BRIDGE iF RESISTIVE LEG B 15 UNBALANCED OUTPUT OF BRIDGE IF REACTIVE LEG 15 DETUNED 8 1464 Figure 4 2 Bridge Waveforms frequency will appear at the bridge output The phase of this signal depends on which leg of the bridge is not tuned or on the relative errors in tuning if neither is set correctly The magnitude of the signal is propor tional to the magnitude of the tuning error of either or both legs of the bridge l 4 24 Figure 4 2a shows a sinusoid input tothe Wien bridge If the resistive leg of the bridge is slightly unbalanced the output of the bridge is very small but has the waveform shown in Figure 4 2b and is in phase with the input As the resistive leg is tuned the signal approaches zero amplitude at null and then becomes larger but 180 out of phase if the null position is passed Whenthe resistive leg is correctly tuned and the reactive leg is tuned through null a Similar waveform is prod
31. o operate for at least 20 minutes to let meter move ment reach normal operating temperature b Turn instrument off and allow 30 seconds for all capacitors to discharge c Rotate zero adjustment screw clockwise un ti pointer isleft of Zero and moving upscale d Continue rotating screw clockwise stop when pointer is exactly at zero e When pointer is exactly over zero rotate adjustment screw slightly counterclockwise to relieve tension on pointer suspension 1f pointer moves offzero repeat steps c through but make counterclockwise rotation less 3 18 DISTORTION MEASUREMENT CAUTION DO NOT EXCEED THE INPUT VOLT AGES LISTED BELOW TO PREVENT DAMAGING COMPONENTS ON 2 BOARD VOLTMETER FUNCTION 1V RANGE AND BELOW AND DISTORTION ANALYZER 575 FUNCTION MAXIMUM SENSITIVITY 1 800 V ABOVE 100 Hz 2 50 V ABOVE 1 kHz 3 19 MANUAL MODE a Turn instrument on and mechanically zero meter according to procedure in Paragraphs 3 15 and 3 16 3 2 Model 333A 334A Set NORM R F DET switch to NORM Set FUNCTION switch to LEVEL Set MODE switch to MANUAL If fundamental frequency is 1kHz or greater set HIGH PASS FILTER switch to IN Set SENSITIVITY selector to MIN position and rotate VERNIER control maximum counterclockwise NOTE The bandwidth of the SENSI TIVITY selector is reduced in the two extreme CCW positions positions used with an input signal greater than 30 V Set METER RAN
32. on operation Capacitive dividers S2C1 through 52 10 in the attenuator keep the frequency response flat The impedance converter is a low distortion high input impedance amplifier circuit with gain indepen dent of the source impedance placed at the INPUT terminals 4 15 Instrument induced distortion of the signal being measured is minimized by keeping the input impedance and the gain of the impedance converter 4 1 Section IV linear The input impedance is kept linear by use of local positive feedback from the source of A2Q1 to the gate of 201 and to the protective diodes A2CR2 and A2CR3 Thus signals with a large source imped ance can be measured accurately Overall induced distortion is further minimized by high open loop gain and 100 negative feedback The high open loop gain is achieved by local positive feedback from the emitter of A2Q3 to the collector of A2Q2 Overall negative feedback from the emitter circuit of A2Q4 to the source of A2Q1 results in unity gain from the impedance converter 4 16 Thebias points of thetransistors in the imped ance converter are selected to minimize instrument induced distortion A2Q1 an extremely low noise high impedance field effect transistor is the major component that makes linearity of the impedance con verter independent of the signal source impedance 4 17 REJECTION AMPLIFIER CIRCUIT Refer to Figures 7 3 and 7 5 4 18 The rejection amplifier circuit consists of t
33. pedance dc restoring peak detector with semi conductor diode operates from 550kHz to greater than 65 MHz Broadband input Maximum input 40 V p p ac or 40 V peak transient CARRIER FREQUENCY 550kHzto 1 6 MHz Distortion introduced by detector is 0 3 for 3 to 8 volt carriers modulated 30 i 2 NOISE MEASUREMENTS Voltmeter residual noise on the 300 pV range 25 u V rms terminated in shielded 6000 30 u V rms terminated in shielded 100 OUTPUT For input frequencies from 20 Hz to 600 kHz 0 1 V rms 0 01 V open circuit for full scale meter deflection 0 05 V rms 0 005 V into 2 for full scale meter deflection AUTOMATIC NULLING MODE Set Level At least 0 2 V rms Frequency Ranges X1 manual null tuned to less than 3 of set level total frequency hold in 0 5 about true manual null X10 through manual null tuned to less than 1090 of set level totalfrequency hold in 1 about true manual null AUTOMATIC NULL ACCURACY 5 Hz to 100 Hz Meter reading within 0 to 3 dB of manual null 100 Hz to 600 kHz Meter reading within 0 to 1 5 dB of manual null HIGH PASS FILTER 3 dB point at 400 Hz with 18 dB per octave roli off 60 Hz rejection gt 40 dB Normally used only with fundamental frequencies greater than 1 kHz POWER SUPPLY 100 v 120 V 220 V 240 V 5 10 48 66 Hz approximately 4 watts 1 6 MHz to 65 MHz Distortion introduced by detector is lt 1 for 3 to 8 volts rms carr
34. resistance changes in photocells that form part of the Wien bridge 4 28 When the bridge circuit is tuned and balanced the voltage and phase of the fundamental which appears at junction of the series reactive leg S4R1 3 5 7 or 9 and C4A B and the shunt reactive leg SAR11 13 15 17 or 19 and C4C D is the same as at the midpoint of the resistive leg A3R12 and A3R14 When these two voltages are equal and in phase the fundamental frequency will not appear at the drain of the field effect transistor A3Q4 For frequencies other than the fundamental the reactive leg of the Wien bridge offers various degrees of attenuation and phase shift which cause a voltage at the output points of the bridge This difference volt agebetweenthe reactive leg and resistive leg is amp lified by A3Q4 A3Q5 and A3Q6 Figure 4 3 illus trates a typical Wien bridge circuit and the rejection characteristics for it 4 29 The Wien bridge circuit is designed to cover a continuous frequency range of over a decade for each position of the FREQUENCY RANGE selector 54 54 provides coarse tuning of the reactive leg by changing the bridge circuit constants in five steps at 1 decade per step For the automatic control loop the refer ence voltage is taken from R6 at the input to the re jection amplifier and applied to the buffer amplifier 597 The reference voltage is amplified and clipped by A5Q8 and 509 and coupled to the detector A5Q4 The output
35. s connectors and indicators The description of each component is keyed to the drawing included within the figure 3 6 GENERAL OPERATING INFORMATION 3 7 INPUT CONNECTIONS 3 8 The input signal can be connected to the 333A and 334A through twisted pair leads or a shielded cable with banana plug connectors Keep all test leads as short as possible to avoid extraneous pickup from stray ac fields When measuring Low level signals ground loops may occur causing erroneous readings Ground loops may be avoided by connecting the 333A 334A Distortion Analyzer to an appropriate isolation transformer to break the chassis ground from power supply ground Connect all other instruments to one power strip with the three prong connectors as close as possible 3 9 VOLTMETER CHARACTERISTICS 3 10 The RMS VOLTS markings on the meter face are basedonthe ratio betweenthe average and effective rms values of a pure sine wave The ratio of average to effective values in a true sine wave is approximately 0 9to 1 Whenthe meter is used to measure complex waves the voltage indicated may not be the rms value of the signal applied This deviation of meter indica tion exists because the ratios of average to effective values are usually not the same in a complex wave as wave The amount of deviation depends on the magnitude and phase relation betweenthe harmonics and fundamental frequency of the signal applied Table 3 1 lists the deviatio
36. s to dBm locate the mental 200 ohm impedance line at the bottom of the graph Follow the impedance line to the If desired rms voltage of input signal can be heavy black line and read the meter correc measured by setting FUNCTION switch to tion at that point The correction for 200 VOLTMETER and setting METER RANGE ohms is 5 dBm thus the corrected reading switch to obtain an on scale indication is 25 dBm 3 3 Section 3 23 METER INDICATION 3 24 The 333A 334A meter is calibrated to indicate in both dB and volts It is interesting to notethat the METER RANGE markings differ from most ac volt meter range markings On most ac voltmeters 600 ohms 0 dB corresponds to the 1 volt range This is not true inthe case of the 333A 334A Since the instru ment is primarily a distortion analyzer measurements are in dB relative measurement rather than in dBm absolute measurement Zero dB the 333A 334A corresponds to 0 3 volt range rather than the 1 volt range This allows 210 dB greater dynamic range of distortion measurements 3 25 If measurements are to be made in dBm 10 dB must be subtracted from the METER RANGE setting Thus 0 dB becomes the 10 dBm range for absolute power measurements Zero dBm is equal to 1 milli watt dissipated by any impedance andinthis particular case is 600 ohms The 10 DECIBELS marking on the meter face indicates that when voltmeter measurements are being made the indication METER RANGE plus
37. sistor parameters with environmental changes In this manner the calibration of the instrument is made dependent on high quality passive components 4 47 METER RECTIFIER CIRCUIT 4 48 The meter rectifier is connected in a bridge type configuration with a diode in each upper branch and a dc milliammeter connected across the midpoints of the bridge The simplified meter rectifier is illus trated in Figure 4 8 The generator represented by A2Q5 through A2Q9 with the internal impedance Ro provides the meter M1 with current for full scale deflection and develops a voltage across the calibra tion network which closes the ac feedback loop Capacitors A2C27 and A2C28 are used as coupling capacitors for the ac feedback loop output signal to the OUTPUT connector and the bridge error signal to the input of the automatic fine tuning loops The mechanical inertia of the meter and A2C26 prevents the meter from responding to individual current pulses Therefore the meter indication corresponds to the average value of the current pulses rather than the peak value The meter is calibrated to indicate the rms value of a sine wave Resistor A2R45 im presses a fixed bias across diodes A2CR6 and A2CR7 biasing them close to the barrier voltage to make the meter amplifier response linear to large variations LonceoccuJ A2R34 Figure 4 8 Section IV in signal amplitude The linearity of this type of cir cuit is also increased by including
38. t in outputs from both resistive and reactive detectors to tune the bridge and reject the fundamental 4 36 When the FUNCTION selector is set to the VOLTMETER or SET LEVEL position the junction of the series and shunt reactive branches ofthe Wien bridge is connected to circuit groundthrough A3R19 by SIBF which disables the frequency rejection characteristic of the bridge circuit With the bridge circuit disabled the rejection amplifier circuit pro vides one dB of gain for the fundamental frequency and the harmonics In the SET LEVEL operation this signal is used to establish the SET LEVEL refer ence 4 37 BRIDGE AMPLIFTER CIRCUIT 4 38 The bridge amplifier circuit consists of three stages of amplification A3Q4 through A3Q6 The first stage of amplification A3Q4 is a field effect transistor which amplifies the difference signal between the gate andthe source The field effect transistor is selected for minimum noise performance with the high impedances of the Wien bridge circuit The signal from the drain is applied to the two stage feedback amplifier A3Q5 and A3Q6 The output of A3Q6 is coupled to the meter circuit by the post attenuator S3R1 through S3R11 Negative feedback from the out put of the bridge amplifier is applied to the preamp lifier circuit to narrow the frequency rejection characteristic It can be noted from the rejection characteristic refer to Figure 4 3 for the bridge that the rejection of harmonic voltages
39. uced Figure 4 2c The only difference is that the reactive signal is 909 out of phase with the resistive signal 4 25 When the bridge output is detected using the input signal as the reference the error signals in phase or 1809 out of phase with the reference develop a voltage that is used to vary the resistance in the resistive leg of the bridge to tune it to the correct null position Signals of the form in Figure 4 2c do not develop any voltage as the resistive detector is in sensitive to inputs differing from the reference by 900 Model 333A 334A TYPICAL WIEN BRIDGE bc v x a 3 z be E p P Section FEEDBACK FREQUENCY Figure 4 3 Wien Bridge Circuit and Rejection Characteristics 4 26 In an independent but similar control loop the bridge input signal is shifted 90 and used as the reference signal for the detector This detector develops control voltages to null the reactive leg of the bridge but is insensitive to signals of the form in Figure 4 2b which are caused by small tuning errors of the resistive branch 4 27 The result is that the two control loops derive information from a common source and develop two independent control signals for nulling the two legs of the bridge These control voltages are used to vary the brilliance of lamps which in turn cause
40. vel to be set up on the meter With the FUNCTION switch in the DIS TORTION position the Wien bridge is used as an in terstage coupling network between the preamplifier and bridge amplifier The Wien bridge is then tuned and balanced to reject the fundamental frequency of the applied input signal Two automatic control loops con sisting of two phase detectors lamp drivers lamps and photocells provide fine tuning and balance in the AUTOMATIC MODE The remaining frequency com ponents are applied to the bridge amplifier and are measured as distortion by the metering circuit Nega tive feedback from the bridge amplifier to the preamp lifier narrows the rejection response of the Wien bridge 4 7 The output of the rejection amplifier is applied to the metering circuit through the post attenuator The post attenuator is used to limit the input signal Section IV iV OPERATION level applied to the metering circuit to 1 mV for full Scale deflection Sensitivity of the metering circuit is increased to 300 uV for full scale deflection onthe 0003V range The metering circuit provides a visual indication of the distortion level of the input signal In addition tothe indication provided by the meter the OUTPUT terminals provide a means of monitoring the distortion components 4 8 DISTORTION MEASUREMENT IN AM CARRIERS 4 9 The Model 334A Distortion Analyzer contains an AM detector circuitfor measuring envelope distortion in AM carr
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