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PUBLISHED BY THE HEWLETT-PACKARD COMPANY 275 PAGE MILL ROAD PA L 0 ALTO CALIFORNIA SEPT. - OCT., 1

For The D C - SeveralA Dual -Trace Automatic Base Line OscilloscopeHundred KC RangeUAL-TRACE oscilloscopes, since they per-Dmit two eparate waveforms to be viewed

simultaneously, considerably simplify work incircuits and systems where changes in waveform

are involved or where time orphase relationships are of inter-est. Fig. 2 shows a representa-tive case where the dual-trace display is of

value.To make available the convenience of the

dual-trace feature in an instrument for the dcto several hundred kc range, the new oscillo-scope shown in Fig. has been designed. Aspecial feature of this instrument is that thedual-trace display is supplemented by an auto-matic base-line provision such that, when nosignal is applied, a low-rate sweep automati-cally occurs. Two horizontal traces are thus pre-sented to make the positions of the base linesfor both vertical amplifiers always known. In

Attenuators p. 3

establishing set-ups and making initial adjust-ments, this feature is of considerable conveni-ence. When a signal to be viewed is then ap-plied, the sweep will automatically triggerfrom the signal in most modes of operation.In its other characteristics the instrument is

designed to be suited to many applications inits frequency range. The twovertical amplifiersare identical with 3 db points above 200 kc andmaximum sensitivities of 0.01 volt/cm. Severaldifferent vertical presentations can be selected,as described more fully later. An internalsquare-wave calibrator enables the vertical sys-tem calibration to be easily checked when de-sired. Calibrated sweep speeds extend down to5 microseconds/cm which can be increased to

microsecond/cm with a x5 sweep expander.The horizontal amplifier has a maximum sensi-tivity of 0.1 volt/cm and is identical in band-width to the vertical amplifiers with less than

Fig. 2. Oscillogram indicating typical instance wheredual-trace oscilloscope permits two-phenomena compari-son, here used t check plate and cathode Waveforms o fphantastron.Fig. (left). New - h p - Model 2224 Dual-Trace Oscillo-scope permits two ghenomena within dc to several hun-dred kc range to be compared simultaneously. Instrumentincorporates no-signal sweep such that base lines areautomatically displayed in absence of signal to facilitateset-up adjustments.

P R I N T ED I N U . S . A . COPYRIGHT 95sHEWLETT-PACKARD c o .

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C r j A N N E L A POLALITY C S L.0 L F I l i pV E R T PRESENTATION

Fig. 3. Vertical presentation selector pro-vides fo r five types of vertical display.Concentric switch inverts A channel sig-nal t facilitate two-signal comparison.2 differential phase shift a t 100 kc.

If desired, differential phase shift at ahigher frequency can be minimizedwith an internal adjustment.VERTICAL PRESENTATIONSThe oscilloscope is designed with afive-position vertical presentation se-lector (Fig. 3 to permit an optimumdisplay to be selected for a given appli-cation. The extreme selector positionsA and B provide for single-channelpresentations, while the intermediatepositions present combinations of thetwo vertical channels, wi th C HO P andALT being the dual-trace displays inwhich the two inputs can be viewedsimultaneously. In the CH OP position,t h e vertical deflection system is elec-tronically switched between the twovertical amplifiers a t a 40 kc rate forsuch purposes as permitting a compari-son of single transients and generallyfacilitating comparison of lower fre-quency signals. If desired, however,chopped operation can be used to viewhigher-frequency signals as well, al-though in the rather remote event t h a tthe signal is harmonically-related a t alow ratio to the 40 kc chopping fre-quency, the detail of the presentationwill be diminished, since the choppingfrequency will be stopped. Alternatesweeping can then be used. For choppedoperation an external trigger is requiredto prevent the trigger system fromsynchronizing on the chopping wave-form.N O N H A R M O N I C A L L Y - R E L A T E D

W A V E F O R M SIn the AL T position the sweep alter-

nately presents the outputs of the twovertical amplifiers. This mode is a gen-eral-purpose mode for dual-trace pre-sentations a t sweep speeds faster thanabout 10 milliseconds/cm with a P1phosphor tube. Besides its general-pur-

100 100Fig. 4. Typical bandwidth122A.Curve applies to allthree amplifiers. Dif feren- 8 6otial phase shift betweenamplifiers is less than22 at 1 kc.characterzstic o f Model 0 80

60

40 401 3 5 10 50KC IOOK 3 500KCF R E P U E N C Y

pose nature, however, this position hasthe special advantage, which is a basicadvantage for the dual-trace type oftwo-channel instrument, t ha t it per-mits nonharmonically-related signals tobe viewed. This occurs because the trig -ger system can alternately trigger fromthe two amplifier outputs. T he featureis thus useful f or such purposes as com-paring time markers with non-inte-grally-related waves where only alter-nate triggering will stop both wave-forms. Where the relative phases ofharmonically-related waveforms are ofinterest, however, an external triggershould be used with alternate operation.Dual-trace displays are additionallyfacilitated by aninverting switch whichis concentric with the vertical presenta-tion selector. This switch changes thepolarity of the A channel presenta-tion to accommodate phase reversals be-tween different pick-off points in thesource.

Fig. 5. Rack-mounting version has beendesigned w ith panel height of 7 inches fo reconomy o f rack space.DIFFERENTIAL PRESENTATION

The B - A position presents the in-stantaneous difference between the sig-nal voltages applied to the A and Bterminals and is thus specifically suitedto viewing signals in differential orbalanced sources. The position is alsoconvenient for mixing two harmoni-cally-related signals of widely differentamplitudes. Common mode voltages onthe differential signal are suppressed bya t least 3 0 db in the B - A position.Differential inputs are also providedon the most sensitive position of eachvertical amplifier. Common mode volt-ages on the applied signal will be sup-pressed in the most sensitive positionby a t l e a s t 40 db.

VERTICAL ANDHO RIZO NTA L RE S P O NS E SThe two vertical amplifiers are de-

signed to be identical and all threeamplifiers in the instru ment are designedto have the same bandwidth (Fig. 4)and phase characteristics. Altho ugh thehigh-frequency 3 db point for the am-plifiers is rated at 200 kc, it is usuallyabout 40% above this. A t the same timeroll-off is slow so that the oscilloscopeis usable at frequencies considerablyabove the 3 db point. The trigger sys-tem will usually respond to frequencieswell above 5 0 0 kc to permit viewingof higher frequency signals.The differential phase shift betweenthe three amplifiers is less than 2 a t100 kc. The A vertical amplifier andthe horizontal amplifier include a phase-adjusting capacitor so that relativephase shift can be minimized a t ahigher frequency if desired.TRIGGER SYSTEM

As mentioned earlier, the trigger sys-tem is designed so that in the absenceof a signal a low repetition rate sweepoccurs to enable the operator to knowthe position of the base line. If the in-strument is set for dual-trace opera-tion, a base line is shown for each am-plifier. When a signal is applied, thesweep will automatically trigger fromthe signal for all bu t chopped presenta-tions, which require the use of an ex-ternal trigger signal. If desired, thepoint on the signal a t which the sweeptriggers can be selected over a rangefrom -10 to I O volts with the Trigger Leuel control. This con trol can alsobe used to disable the automatic baseline sweep when desired.For cases where it is desired to ex-amine a port ion of a display in moredetail, the sweep can be expanded 5times with a switch on the panel. Theoperation is such that the center 2 cmof th e screen is expanded to ful l screenwidth, while any 2 cm portion of theunexpanded sweep can be selected forexpansion with the horizontal position-ing control.The sweep expansion feature can alsobe used to increase the fastest sweep of

Concluded o n p. 4 )

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T W O HIGH-PERFORMANCE ATTENUATORSTTENUATORS for use in the re-A gion between the ultrasonic rangeand waveguide frequencies have, in

general, had one or more of several dis-advantages such as being non-adjust-able, having only a limited attenua-tion range, being non-direct reading,or, in the case of the cutoff type,having a high insertion loss. T o over-come these disadvantages, two new 0ohm variable attenuators have been de-signed to provide a total of 132 db of

Fig. 1. As a pair, new -hp-Models 355A/BSO-ohm Attenuators provide from 0 t o132 db of attenuation in db steps overdc t o 500 mc frequency range.

attenuation in 1 d b steps over th e fre-quency range from dc to 500 mega-cycles. One attenuator provides from 0to 120 db in 10 db steps, while thesecond provides fro m to 12 db in 1db steps. Each attenuator has been de-signed with a single direct-reading con-trol both to achieve simplicity of usefor typical bench work as well as topermit the attenuators to be incorpo-rated easily into panel or console in-stallations. For such installations it isfeasible to mount the attenuators inelectrically convenient locations withinan equipment bay and either t o providerigid or flexible shafts to operate themfro m the panel (Fig. 2 or t o remotelyoperate them with suitable steppingmechanisms. The units are also de-signed with a small cross section sot h a t , in permanent installation applica-tions, they can easily be mounted di-rectly behind a panel as well.C O N S T R U C T I O N T E C H N IQ U E

The basic approach in the design ofthe attenuators has been to extend theresponse of conventional lumped-ele-ment configurations to a high fre-quency by closely controlling strayparameters. Both attenuators consist of

3

THE DC-500 AAC RA NGEa series of pi pads which are connectedin cascade to permit a matched 0-ohminput and output impedance to beachieved a t all attenuation levels. Inhigh-frequency attenuators of this typeit is necessary to locate the pad switchesphysically very close to the individualpads, but in order to avoid the need formanually operating a multiplicity ofswitches and t o achieve the remote con-trol feature described above a designhas been evolved that operates the in-dividual switches from a single shaf t .This shaft mounts four cams whichoperate small sensitive-type switches.These in turn connect the appropriatepads in or out of the network as thecontrol knob is rotated. Since the a t -tenuator is designed as a cascade ratherthan a ladder type, any combination ofpads can be switched in this mannerwithout altering the YO-ohm input oroutp ut impedance.

Each attenuator consists of fourpads. In the 120 db unit these havevalues of 10, 20, 3 0 and 60 db. In the12 db unit the values are 1, 2, 3 and 6db. The pads are con-

I [ ~ T T E N U A T O RFig. 2. Single-shaft operation permitsattenuators t be mounted in suitable lo-cation within racks and operated frompanel w ith flexible shafts or steppingmechanisms.these measures was tha t the response ofthe 10 db pad was down 1 db a t 1700mc, the 2 0 db pad a t 1100 mc, and the3 0 db pad a t 700 mc. Two of the 3 0 dbpads were then cascaded to form the60 db pad. In the 0 to 12 db unit theresponses were comparable or wider be-cause of the smaller resistance values.

Isolation between each pad input and

of the pads wYs consideredseparately and its per-formance optimized as anindividual network. Bymounting the resistors andswitches on a suitablealuminum block, it waspossible to con trol resistorlead length and capacityto ground as well as toachieve repeatability ofthese factors in produc-tion units. The impedanceof the individual sectionswas then checked and ad-justed to T O O mc withthe hp Model 803A VHFImpedance Bridge1. In the120 db unit the result ofA r t h u r Fong, Direct Measure-ment of Impedance in the 50 500MC Range, Hedett-PackardJournal, Volume 1, No. 8,

April , 1950 .

structed with precisioncarbon film resistors fora frequency response well 3 8Q ibeyond 00 mc. Such a ~2range is possible when care

5is taken with lead induc- Q=tances and where capaci-ties are closely controlled. 83+In the design stage each 3+-0. I K C 2 5 I K C I OKC IOOK I M C I O M C I O O M C

F R E Q U E N C Y

1 2

21 0A

1.2

1 0I K C 2 5 I K C I O K C I O O K C IMC I O M C 1 0 0 M CF R E Q U E N C Y

Q = o IKC 2 5 I K C I O K C IOOKC IMC IOMC IOOMCh F R E Q U E N C Yp U l t l lQ = o IKC 2 5 I K C I O K C IOOKC IMC IOMC IOOMCh F R E Q U E N C Y

Fig. 3. Typical accuracy, uswr and irtsertion losscharacteristics o f -hp- 355AIB.

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I N P U T O U T P U fR OROUTPUT INPUTFig. 4 . Overall dimemions of -hp- 355A/B.Adapter noted can be used for ntercon-nection. Solid-shielded cable assembliesare also available.output is achieved by symmetricallydisposing each pad into two compart-ments of a cast aluminum box. Connec-tions between pads are constructed as5 &ohm lines. A number of designs weretried for these lines, but the simplestand most controllable was found to bea straight bare wire placed next to amovable ground plane and insulatedtherefrom by an insulating tape film.The arrangement is such tha t the sepa-

ration of wire and ground plane can beadjusted after assembly to refine theline impedance to the required degree.The operation of the integrated uni twas then checked against a standardcutoff type attenuator.

These measures have resulted in theperformance indicated in Fig. 3 whichrepresent th e tolerances established forproduction units. The characteristicsare not controlled above 500 mc, butthe units are ordinarily useful to muchhigher frequencies for simple level-set-ting and similar usage where step ac-curacy is not a factor. Transient re-sponse has also been checked withpulses of a few millimicroseconds' risetime without discernible waveshapechange.S P E C I A L M O U N T I N G

C O N S I D E R A T I O N STo facilitate side-by-side mounting

of the attenuators, the terminals arephysically located in complementarypositions, as shown in Fig. 4. A ny seriesarrangement can be used for connectingthe terminals and any terminal can beused for input or output, but the ar-rangement indicated in Fig. 4 is con-venient in that it permits a type UG-491A/U adapter to interconnect the a t -

DUAL-TRACE SCOPE some 15 0 volts of common mode de-generation and with regulated tubeheaters. Transistors are used as the con-trol elements in the heater regulator.The main rectifier circuit for the in-strument uses silicon rectifiers for longlife and low heat dissipation.

(Continued from p. 2)the instrument from psec/cm to 1psec/cm.GENERAL

To insure stability, the low-level ver-tical amplifier stages are operated wi th

tenuators. For inpu t and outp ut cables,the wide range of attenuation of theunits makes it necessary to use double-shielded cable such as RG-5 /U . Specialsolid-shielded cable assemblies are alsoavailable to provide a still higher mea-sure of shielding.

-Arthur Fong and Harley L. Haluerson

SPECIFICATIONShp M O D E L S 3 5 S A / B

A TTE NUA TO RSATTENUATION: -hp- 355A, 12 db in 1 d b steps;-hp- 3558, 120 db i n 10 db steps.FREQUENCY RANGE: Dc to 500 mc.OVERALL ACCURACY: -hp- 355A, e0.25 db, dcto 500 mc; -hp- 3558, e l db, dc to 250 mc,-C2 db, 250 to 500 mc.NOMINAL IMPEDANCE: 50 ohms.MAXIMUM SWR: 1.2 to 250 mc, 1.5 tu 500 mc.MAXIMUM INSERTION LOSS: 0 at dc, 0.4 db atPOWER DISSIPATION: 0.5 watt average; 350CONNECTORS: Female type BNC.WEIGHT: 11/z Ibs. net; shipping weight 3 Ibs.PRICE: -hp- Mode l 355A Attenua tor $125.00.-hp- Model 3558 Attenuator,'$125.00.ACCESSORIES AVAILABLE: 803A-16E solidshield 50-ohm Cable Assembly, 15 incheslong with male BNC connectors, $9.00.

803A-16D RG-55/U Cable Assembly, 2 feetlong, terminoted by a male type N connectoron one end and a male BNC connector on theother. $8.50.

60 mc, 1 db ot 250 mc, 1.5 d b a t 500 mc.volts peak.

Prices f.0.b. Polo Alto, C aliforni aDota subiect to change without notice

A rack-mounting version of the in-strument (Fig. 5 ) has been designedwith minimal panel height 7 inches)to conserve rack panel area.Other characteristics of the instru-ment are given in the accompanyingspecifications. -John Strathman

SPECIFICATIONSM O D E L 1 2 2 A

DUAL TRACE OSCILLOSCOPESWEEPSweep Ronge: 15 Cal ibr ated sweeps, accurateto within k5 , in a 1 2, 5, 10, . . . se-quence, 5 psec/cm to 200 millisec/cm. Ver-nier permits continuous odiustment of sweeptime between calibrated steps and extendsthe 200 millisec/cm step to ot leost 0.5sec/cm.Sweep Expond: X5 sweep expansion may beused on oll ronges ond expands fastestsweep to 1 psedcm. Expansion i s obout thecenter of the CRT and exponded sweep ac-curacy i s t l O .Synchronizofion: Interna lly from vertical de-flection signols cousin9 1/2 cm or more ver-tical deflection, f rom line voltage, and fromexternol signols 2.5 volts peok-to-peak orgreater.Trigger Poinf: Automotic. Control overridesoutomotic and permits the trigger point tobe set between -10 ond +10 volts. Turn-ing fully counter-clockwise into AUTO re-stores outomotic operation.

-hp-

VERTICAL AMPLIFIERSBondwidth: Dc coupled: dc to 200 kc.Ac coupled: 2 cps to 200 kc.Bondwidth i s independent of colibroted sen-sitivity setting.Sensitivify: 10 millivolts/c m to 100 volts/cm.4 colibroted steps accurate within i 5 , 10mv/cm, 100 mv/cm, 1 v/cm ond 10 v/cm.Vernier permits continuous odjustment ofsensitivity between steps and extends 10v/cm step to a t leost 100 v/cm.

Infernal Calibrotor: Calibrat ing signal auto-maticolly connected to vertical amplifier forstandardizing of gain, accuracy k2 %.Input Impedonce: 1 megohm, less thon 70 ppfshunt capacitance.Phase Shiff: Vertical and horizontol amplifiershove some phase chorocteristics within & Z 0to 100 kc when verniers are fully CW.Bolonced Input: On 10 mv/cm ronge on bothamplifiers. Inpu t impedance 2 megohmsshunted by less thon 35 ppf. kornmon moderejection i s at leost 40 db. Common modesignal must not exceed +3 volts peak.Difference Input: Both input signols may beswitched to one chonnel to give differentiolinput on ol l vert ical sensitiv ity ronges. Thesensitivity switches m a y be set separatelyto allow mixing signals of different levels.C o mmo n mode rejection i s ot leost 40 dbwith both switches on most sensitive ronge,30 db on other ronges.HORIZONTAL AMPLIFIERBondwidfh: Dc coupled: dc to 200 kc.Ac coupled: 2 cps to 200 kc.Bondwidth i s independent of calibrated sen-sitivity setting.Sensitivify: 0.1 volt/cm to 100 volts/cm. 3colibroted steps, accurote within +5 , .1v/cm, 1 v/cm, and 10 v/cm. Vernier permitscontinuous odiustment of sensitivity betweensteps ond extends 10 v/cm step to ot leost100 v/cm.Input Impedance: 1 megohm, nominal, shuntedby l ess thon 120 ppf.

Prices f.0.b. Palo Alto, C olif orniaDato subiect to chonge wit hout notice

GENERALCafhode Ray Tube: 5AQPI mono-acceleratornormolly supplied; 2500 volt acceleratingpotenti al. P7 and P11 phosphors ore 0150avoiloble. P2 i s ovailable if desired forspeciol applications.CRT Bezel: Light proof bezel provides firmmount for oscilloscope camera and is re-moved easily for quick chonge of filter.CRT Plates: Direct connection to deflectionplates via terminols on rear. Sensitivity op-proximately 20 v/cm.Intensi fy Modulofed: Terminals on rear. +20 vto blonk troce of normal intensity.Filter Supplied: Color of filt er compatible wit hCRT phosphor supplied.lllu mino fed Groficule: Edge lighted wit h con-tro lled il lumi noti on. 10 cm x 10 cm, markedin cm squores. Major horizontol and vertical

axes hove 2 m m subdivisions.Dimensions: Cobinet Mount: 93h wide, 15high, 21Vi deep.Rock Mount: 19 wide, 7 high, 211h deep.19% deep behind panel.Weiohf: Cobinet Mount: Net 35 Ibs.. ShiDDincl5 r Ibs.Rack Mount: Net 33 Ibs., shipping 48 Ibs.Power: 115/230 volts f10%, 50-1000 cps; ap -proximately 150 wotts.Accessories Avoiloble: AC-83A View ing Hood,foce-f itt ing molded rubber, Price: 4.50.Price: Model 122A Cabinet Mount: $625.00.Model 122AR Rock Mount: $625.00.Normally supplied with P1 phosphor. Whenordering P2*, P or P11, specify by addingphosphor number after model.*P2 i s not recommended for generol purposeusage.

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