BRC the Notebook 20

7/30/2019 BRC the Notebook 20

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I WINTER, 1959

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YOU WILL FIND. . .N o i s e l i m i t e d

Receiver Sens i t iv i t yM e a s u r e m e n t T e c h n i q u e . . . . . . . . . . .M o r e About T r ans i s t o rM e as u r e m e n ts w i t h t h eHF-VHF B r i d g e ................... 6M ee t O u r Rep r es en t a t i v es ............ 7E d i t o r s No t e ....................... 8

NUMBER 20

Noise Limited Receiver Sensitivity Measurement TechniqueJohn P. VanDuyne , E n g i n e e r i n g M a n a g e r

As the communication industry pushedabove 30 mc, especially as stimulated bythe pressures of World War 11, it wasfound that the external noise sources haddropped to negligible proportions, com-pared to internal receiver noise, above100 mc. The need for greater and greaterradar sensitivity, VHF communicationrange, and less snowy TV picturesrapidly pushed internal receiver noisedown to the level where cosmic radiobackground radiation (popularly calledcosmic noise, due to its randomly fluc-tuating character) limits useful receiversensitivity from 30 to 100 mc, or downto 10 mc in the absence of man-madeand atmospheric noise. Recent advancesin low-noise receivers and high-resolu-tion antennas used by radio astronomersare resulting in distribution maps ofthis radiation3In spite of their widely differentorigins, cosmic noise and internal re-ceiver thermal agitation voltages aresimilar in character and pose similarmeasurement problems. Man-made andatmospheric noise are very different, inthat they have a discrete impulse natureand require different measurement andsystem evaluation technique. The readeris referred to A. S. A. Standards C63.2and C63.3 for a discussion of theirmeasurement. The term noise used inthe following discussion refers to ther-mal agitation phenomena unless other-

wise qualified.Measurement ObjectivesA general word should be said withregard to the effect of the objective ofthe measurement on the choice of meas-urement technique. These objectives fallin several categories, the most commonof which may be stated as follows:1. The comparision, on a uniformbasis, of equipments of the samedesign, or from the same process.2. The comparision of equipment

of basically different designwith similar desired preformancefor purposes of selecting thsuperior design.3. The study of equipment performance with the in tent of improvinit by redesign.4. The study of equipment .performance for the purpose of learninmore about the physical principleon which it operates, or to evaluatthe extent to which the measureper formance approaches ththeoretical limit.

The techniques to be discussed require increasing degrees of skill and precision as the objective changes from(1 ) to (4) above.Noise Limited Sensitivity CriteriaAs previously mentioned, the recetion of weak radio signals below 30 mwas limited by external noise. Hencwhen measured under laboratory condtions, such receivers seemed noiselesssince they had only sufficient amplifiction to produce rated output on signasupplied by a much noisier source thathe laboratory signal generator. Therfore, the early concept of sensitivity wa specification of the input requirebehind some specified network (dummantenna) to produce a prescribed ouput. Long range communications opeators found such receivers inadequawhen used in quiet locations on wedesigned directional antenna systemConsequently, amplifications were i

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T H E N O T E B O O K

function of the carrier-to-noise ratio. Itis also a function of the I. F.-to-A. F.bandwidth ratio and it varies with theshape of the amplitude-vs-frequency re-sponse curves of these two portions ofthe receiver. In general, however, if thecarrier-to-noise ratio into the detectorexceeds 10 db, the errors in the out-put signal-to-noise ratio becomes neglig-ible. Figure 1, taken from reference 4,illustrates this fact. For further detail onthis matter, the reader should consultreferences4, 5, and 6.

It should be noted, especially, incomparing different receiver designs forweak signal performance, that the effectsof the second detector on output signal-to-noise ratio will not show up with astandard ensi measurement. For thisreason the ensi measurement has givenway in many specifications, to the mea-surement of sensitivity as fi e input, be-hind a specified source impedance, re-quired to produce a stated output witha specified minimum signal-to-noiseratio. In evaluating equipments undersuch a specification, the second detectoreffects will usually be pegligible if, theoutput signal-to-noise ratio is 10 dbor more and if the noise-free transfercharacteristic of the detector is linear.An additional proposal for a sensitiv-ity figure which combines the conceptof maximum gain with the limitations

imposed by the receiver internal noiselevel has been suggested by J. M. Pet-tit.7 In this proposal, the concept ofstandard gain setting is introduced.This is defined as the setting of thegain control which permits the deliveryof a previously decided upon standardnoise output to a specified load. Thisstandard noise output must be specifiedfor a given class of service and forspecific equipments. For example, itmight be specified as 0.5 milliwatts in600 ohms as is typical for some com-munications equipment. The procedurefor measurement is to connect the testequipment to the receiver, but with thesignal generator adjusted for zero out-put. The receiver gain control is thenadjusted for standard noise output. Theoutput of the signal generator is thenincreased until standard output is ob-tained on the output indicator. The levelfrom the generator is then noted as thereceiver sensitivity. If standard noisemum gain or a maximum sensitivitycriteria is used as previously discussed.This procedure is a formalization ofoutput is not achieved, then a maxi-

OUTPUT4-TE R MINA L NETWORK CIRCUITIGN A L GENERATORr)

INPUT OUTPUTTERM. TERM.0 0 0I I- I U

Attenuator of character-istic impedance R an dattenuation >>1

S Signal power available at the outputtermlnals of he 4-terminal network.

N Noise power available at the outputS, Power availabl e at Sig. Gen. Output terminals of the network.terminals.V l5 =y

G S/S, which depends on generator irn-pedance but not on load connected tanetwork. This i s defined fo r midbandfrequency of network.

Figure 2a. Equivalent Circuit for Noise Figure Definition

the previously mentioned general classof sensitivity specifications which statean input signal level for a specifiedsignal-to-noise ratio.The measurement precautions men-tioned under the discussion of ensi ap-ply to any sensitivity measurement in-volving the ratio of single-frequencypower to the power in a noise spectrum.

Noise FigureIn an effort to work out a more basicmeasure of receiver performance whenlimited by random noise, several work-ers proposed rating the noise character-istics of a receiver, independent of itsamplification. The specific proposalwhich has come into general use is thatby D.O. Norths. A later paper by Friis9developed a more rigorous general def-inition of Noise Figure. This allowedthe concept to be applied to networksgenerally. In addition, Friis developedtechniques for handling the noise per-formance of networks in cascade. Thiswork permits calculation of a systemnoise figure from that of its compo-nents or vice versa.

Figure 2a shows the general circuitanalyzed. The concept of available poweris used in this analysis to avoid loss ofgenerality due to dependence on thereceiver input impedance or the loadconnected to the receiver output. Friisdefines Noise Figure of a network(sometimes called Noise Factor and Ex-cess Noise Ratio) as the ratio of theavailable signal-to-noise ratio at the sig-nal generator terminals to the availablesignal-to-noise ratio at its output term-

inals. From Figure 2b, we have thavailable signal-to-noise ratio of the generator as S,/KTB and that for the nework as S/N.

AvailablePower

r.hermal Noise = P.4KTRB

4RP, = -- - KTB watts.

e, =equivalent Thermal noise voltage.e,? =4KT where K =1.38 x 1O-13.Thus, the available signal-to-noise ratio fthe above generator i s SJKTB, and the nwork output available signal-to-noise rai s S/N.(From Fig. 1, p. 419 of Reference 9)

Figure 2b.a Resistor

Available Thermal Noir e Power fro

If FENoise Figure, we have by oustatement aboves,-TB S, NX -;2 ) F = - --S S KTBN-

( 3 )

( 4 )

Sbut G -;s,Nso F z GKTB

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( 5 ) or N =FGKTB, which includesthe amplified signal generator thermalnoise power GKTB so the available out-put noise, due only to sources in thenetwork, is (F-1) GKTB.For simplicity, the usual measurementmethod is to adjust the attenuator A(Figure 2a) such that the output noisepower is doubled by the generator sig-nal. Under this condition, S =N andfrom equation ( 2 ) :

( 6 ) F = - __ V2-,KTB RAKTBV2Aif e2, =-where e, is in microvolts delivered to aload from an R ohm source- implicit

due to our use of the avai lablepower concept).K =1.38 x 10-23 (BoltzmansB =bandwidth in kcT =290 Kelvin (1 7C )R =generator source in ohms

constant)

(for arithmetic convenience)

e2,F =- x 1064RB (as a power ratio)(e2. x 106)-( 7 ) or Fdb=10 log 4RBIt is important to note that the band-width B introduced in Figure 2b repre-sents the bandwidth of an equivalentrectangular power pass band of gain Gand an area equal to that under the ac-tual power gain vs frequency curve ofthe device being tested. In mathematicalnotation,

1 r o D

where GtE vailable power gain atfrequency f.G =available power gain atthe frequency of the CWmeasurement.

In a practical case, B may be deter-mined by plotting the squared ordinatesof the voltage gain vs frequency ch veas a function of frequency, calculatingthe area of the resulting curve graphi-cally, and dividing by the value of G atthe specific frequency, within the pass-band, to which the generator in Figure2a is tuned.

I PI F OUTNARROW BAND POWERVARIABLE FREQ-CW OR RANDOM NETWORKSTANDARDNOISE UNDER DETECTORGENERATOR TEST 1.F: FILTER

Figure 3. Single Frequency Noise Fi gure- . F. Filt er Met ho d

Alternative to the use of a CW signalgenerator is the use of a random noisegenerator such as a temperature limiteddiode. This permits a simpler measure-ment to be made, without the need todetermine B, but yields an answer whichis actually the mean value of F. Forpurposes of receiver front-end evalua-tion, this is often sufficient, but forthe evaluation of the noise figure ofnetworks involving modulation or de-modulation, or cascaded networks of dif-ferent bandwidths, or networks in whichthe source resistance is a variable withfrequency, the measurement of singlefrequency noise figure is often neces-sary if proper evaluation is to be made.

I. F. noise spectrum is much wider than1/2 of the I. F. response (Reference 6),thus when using the I. F. filter methodof Figure 3, a much narrower than ex-pected I. F. filter is required. By the useof a CW generator and A. F. filter (Fig-ure 4 ) , useful data on the variation ofsingle frequency noise figure through anetwork pass band can be derived rathersimply. In solving equation 8 it shouldbe noted that the value for G is thatwhich corresponds to the frequency ofmeasurement in the pass band. The re-sulting value of B is used in equation( 7 ) to solve for the single frequencynoise figure.There are several types of measure-

A.E OUT -

Note: the standardization of the output power detector for a 3db output power increase should beaccomplished by introducing a known 3db change in IF gain.

Figure 4. Single Frequency Noise Fi gure- . F. Filter Method

The single frequency noise figureconcept as distinct from the mean noisefigure (which is what has been de-scribed above) is thoroughly discussedmathematically in reference (10). Theclassical method of measurement is toinsert a variable center frequency nar-row-band filter between the networkbeing measured and the power detector.The single frequency noise figures whichresult from measurement through eachcenter freqyency of the narrow filterare then weighted by their relative gainsand averaged. See Figure 3 for thisset-up. Since this technique is often in-convenient, a frequently useable ap-proximation results from the use ofa CW generator, a narrow-band A. F.filter, and a power detector as in Figure4. The A. F. noise spectrum resultingfrom wide-band demodulation of an

ment for which the CW noise figuremeasurement is necessary. A typical oneis the case of a receiver with a selectivefilter ahead of the first noise sourcewhich is comparable to the I. F. selec-tivity. In this case, a temperature limiteddiode measurement with a wide-bandpower detector may indicate a poor noisefigure (mean noise figure). Measure-ment with a single frequency methodmay disclose a good band center noisefigure, but with rapid deteriorationtoward the band edges, which indicatesan incorrect choice of R. F. selectivity,impedance match compromise, or toowide a coupling circuit between the firstand second stages of amplification if thesecond stage contributes appreciableoise.solving equation ( 7 ) for e,.Some interesting data results from


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1 1 I I5 I O 15 20.01 '0 NOISE FIGURE ( db )Figure 5. Values of e, for Various Noise Figures and Bandwidths

( 9 ) e, =J 4RBx antilog F mFigure 5 plots these results for severalbandwidths and for R =50 ohms. Note,for example, that with a noise figure of3 db and a bandwidth of 3 kc, the inputsignal, eH, equired to double the avail-able noise power output is 0.035 mic-rovolts. This is approximately true for avoice frequency VHF A. M. communi-cations receiver of good design. Obvi-ously, a generator of extremely .lowleakage and good low-level calibrationis required to make this measurement.

An external 40-db pad is usually re-quired to reduce the usual 1.0 -pvminimum level to the order of 0.01 pv .

There are several sources of error innoise figure measurements. Typical arethose associated with the super-hetero-dyne selectivity of the receiver undertest. In general, the I. F. and image fre-quency rejections must exceed 10 db ifsignificant error is to be avoided. It isinteresting to note that such spuriousresponses will give a pessimistic (h igh)noise figure if a CW generator is used

for the measurement, but an optimistireading if a broad-noise spectrum generator is used. This is due to the facthat in the former case, the receiver iexposed to unwanted noise generator(I. F. or image) which have no signacounterpart.

Another source of error may occur inthe determination of the doubled outpunoise power. This is not as critical as inthe case of the ensi measurement, sincthe detector output with a CW signal aa 3-db signal-to-noise ratio is largelcomposed of noise sidebands. The besmethod is to calibrate the I. F. amplifiefor a 3-db gain differential, so that thdetector operating point stays the sameIf the device permits, insertion of a 3-dattenuator is best, if it can be donwithout an accompanying change ibandpass. Alternatively, the gain controcan be calibrated for a 3-db gain changeEither of these two methods can be useto calibrate the detector characteristic tanswer the question of its power response. It should be noted that any attempt to use a modulated signal fonoise figure measurement is beset witall the errors of the ensi method anshould be avoided.

A precaution which is important tall sensitivity measurements, but especally so in the case of noise figure, is thneed to accurately control the generatosource impedance and noise temperature. In the absence of contrary sytem requirements, a resistance shoulbe used equal to the nominal transmission line impedance for which the receiver is designed and corrected to 290'K from the actual temperature.ConclusionSensitivity measurements made on rceivers which have sufficiently low internal noise to detect thermal noise the source are among the most exactinwhich can be made on a radio receiveGood results require good equipmencareful set-up, and careful experimenttechnique. Most important, however, a thorough understanding of the theretical basis of the measurement and thuse to which the results are to be puThe precautions and suggestions in thpreceding discussion have all been thooughly proven by extensive use in thlaboratory and are offered to the reada.s a guide to be t te r exper imentprocedure.

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References ceivers - ubini and Johnson, Proc. of1. Reference Data for Radio Engineers - I. R. E., Dec. ' 4 8I. T. and T. Labs. Second Edition P. 244, 245 5 . Rectification of Sinusoidally Modulated2. Standard for Measurement of Radio Carrier in the Presence of Noise - iddle-Receivers- . R. E. 1938 (Published 1 9 4 2 ) ton, Proc. I. R. E. Dec. ' 4 83. The Distribution of Cosmic Radio 6. The Effect of Fluctuation Voltages onBackground Radiation - . C. KO, Proc. the Linear Detector - . R. Ragattini, Proc.of I. R. E., Jan. ' 5 8 of I. R. E., June 1942, J. M, pettit in "VHF Techniques" by. Signal to Noise Ratio in A. M. Re-

Radio Research Lab. - Vol. 2 , Ch. 2 5 ,P. 6 4 2 .8. "The Absolute Sensitivity of Radio Re-Jan.eivers"942- . 0. North, R. C. A. Review,9 . Noise Figures of Radio Receivers -H. T. Friis*10. Vacuum Tube Amplifiers - Valleyand Wallman, M. I. T. Series Vol. 18P. 59 9 and P. 696

Of I. R. E., July 1944

More About Transistor MeasurementsWith The HF-VHF Bridge

GEORGE P. McCASLAND, S a l e s Engineer

The response to the transistor meas-urement article, which appeared in Note-book No. 19, was gratifying indeed.Many helpful suggestions.and criticismswere received from Notebook readers.Your author hopes that the informationpresented here will serve to correct andclarify' several points in question.

hZ lb and h lZb FormulasThe derivation of h21b as explainedin the appendix to the original articleis not entirely correct. Diagram 4 onpage 5 of Notebook No. 19 shows e l

to be positive toward the emitter ter-minal of the transistor. In diagram 7,on the other hand, el is shown positivetoward the base terminal. Actually, cur-rent flow shown in both cases requiresthat el be positive toward the emitterterminal. Therefore, the derivation ofthe h21b formula should have beengiven as:

i l =- 1- c ) i e rom diagram ( 7 )

e lNow: h l l b =- rom diagram ( 4 )i e

In deriving the formuhs for hzlb andh12b, certain approximations were madewhich were not specifically mentionedin the original article. Formal networktheory shows these approximations. Forexample, from the table of Matrixes of3-Terminal Networks on page 506 ofReference Data fo r Radio Engineers, byI.T.T. we find that:

From page 503 of the same book:d =h11 h2z--h12 h21-h12 +A21 +IAh=h l l h22 - 4 1 2 h21,and

for junction transistors:Ah


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MEE T O U R REPRESENTATIVESBlVlNS AND CALDWELL

HARRY J . LANG, S a l e s M a n a g e rBivins and Caldwell, Inc. was founded

by John F. Bivins and David J. Caldwellshortly after their return to High Point,North Carolina at the close of WorldWar 11, in the belief that electronicsand radio communications would playan incceasingly important role in thefuture industrial development of theSouth. The specific need for a technicalgroup to provide local customers withsales and application engineering serv-ices on complex electronic equipmentwas apparent and the partners formedtheir organization to represent leadingmanufacturers of communications andelectronic laboratory test equipment.Both partners, by virtue of their back-grounds, brought a wealth of specializedexperience to the new company. JohnBivins majored in physics and engineer-ing at Duke University and had beenin the radio and communications busi-ness in High Point for nearly ten yearsprior to World War 11. Dave Caldwellmajored in physics and engineering atDavidson, taught physics at that schoolfor two years after graduation, and laterheld posts in the production and costaccounting fields. During the War, DaveCaldwell served in the Planning Section( G 3 ) of the Army, and John Bivinswas employed as a special engineer withthe Navy Department, dealing withplanning and supervision of Radar in-stallations on Naval vessels.Industrial expansion throughout theSouth during the past eight years di-rectly confirmed the early beliefs ofBivins and Caldwell and also broughtabout a decisive change in the Bivinsand Caldwell organization. While broad-casting equipment accounted for themajor portion of their business up untilapproximately 1949, the rapid growthof electronic manufacturers and relatedindustries, created increasing demands

for specialized services in the applica-tion of electronic instrumentation andthe organization now handles precisionelectronic laboratory equipment exclu-sively. Bivins and Caldwell joined BRCin 1952 and has continuously handledour products since that time.With increased business activity camethe requirement for expansion of thecompanys personnel and facilities. C.M. Smith, Jr. joined the expanding com-

H e a d q u a r t e r r o f B iv i n s a n d C a l d w e l l , I n c . i n H i g h P o i n t , N. C .The companys facilities have alsobeen increased, with branch offices inAtlanta, Georgia, and Orlando, Florida.The new headquarters building in HighPoint is one of the most modern andbest arranged office facilities in thearea. The Service Department here, un-der the direction of Mr. Robert LMoore, has complete repair and recali-bration facilities and is well equippedto service all products that are currently handled. All offices are equipped

pany in 1950. Smitty is an engineer-ing graduate of North Carolina StateCollege with extensive communicationsengineering experience. During WorldWar I1 he served as an Electronics Of-ficer with the U. S. Navy and was aninstructor at the famed M.I.T. RadarSchool in Boston, Mass. Later additionsto the staff have increased total per-sonnel to over 21; 9 of which are fieldengineers who concentrate exclusivelyon customer problems.

S h o w n in c on f e r enc e a r e , l e f t - t o -r i gh t ,J ohn B i v i ns , Doug las S ev e r enc e , Dav id Ca l dw e l l , and C. M. Smith , Jr.


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with TWX service for efficient com-munication with all factories. The com-pany also maintains a fleet of eight ve-hicles for use by field engineers. TheBivins and Caldwell Fall Road Show,which runs for about four weeks, coverssome 4,000 miles and is an annual eventattended by several thousand engineersin the local area.

Bivins and Caldwell believes thattheir organization must operate on thepremise of fundamental engineering in-tegrity. Their basic objective is to assistcustomers in solving engineering prob-lems and to recommend the best avail-able test equipment and techniques forthe particular job to be done. We atBRC proudly salute Bivins and Caldwellfor their faithful service to our manyvalued customers throughout the South.

EDITORS NOTEJohn P. Van Duyne Appoi ntedEngineering Manager at BRC

The appointment of John P. Van-Duyne as Engineering Manager, effec-tive August 18, 1958, has been an-nounced by Dr. George A. Downs-

brough, President. Mr. Van Duyne comesto BRC with 15 years of experience inthe fields of engineering and electronics.The major part of his experience hasbeen in the development and produc-tion of electronic instruments.After receiving his Bachelorof Sciencedegree in Electrical Engineering fromRensselaer Polytechnic Institute of Troy,New York in December 1943, Mr. VanDuyne served with the U. S. SignalCorps where he instructed in radar andradio relay techniques. During his lastyear of service, he was engaged in thedesign of Radio Countermeasures epuip-ment in the Coles Laboratory at FortMonmouth, New Jersey.Following his discharge from the Sig-nal Corps in 1946, Mr. Van Duynejoined the Measurements Corporationof Boonton, N. J. as Project Engineerand was engaged in the development ofsignal generators.In August 1948, he became associatedwith the Allen B. DuMont Laboratories,East Paterson, New Jersey, serving suc-cessively as Senior Engineer, SectionHead of the Advanced DevelopmentSection, and Section Head of the Cir-cuit Design and Development Section.From March 1953 until he joinedBRC in August, 1958, Mr. Van Duyne

AL8IIOLIERQUE New Mexico- - - - -, .GENE FRENCH COMPANY120 Son Pedro Drive, S . E.Telephone: AMherst 8-2478TWX: AQ70

ATLANTA. GeoroiaBIVINS C A L ~ W E L L3133 Maple Drive, N.E.Telephone: CEdor 3-7522TWX: AT 987BINGHAMTON, New York

E. A. OSSMANN B ASSOC., INC.147 Front StreetVertol, New YorkTelephone: ENdicott 5.0296BOONTO N, N ew J erseyBOONTON RADIO CORPORATIONlntervole RoodTelephone: DEerfield 4-3200TWX: BOONTON NJ 866BOSTON, Massachusetts

INSTRUMENT ASSOCIATES1315 Mosrochusetts AvenueArlin ton 74, Moss.Telepxone: Mlssion 8-2922TWX: ARL MASS. 253CHIC AGO 45. IllinoisCROSSLEY ASSOS., INC.2711 West Howord St.Telephone: SHeldroke 3-8500TWX: CG 508DALLAS 9. Texor

DAYTON 19, OhioCROSSLEY ASSOS., INC .53 Pork AvenueTelephone: Axminster 9-3594TWX: DY 306DENVER, ColoradoGENE FRENCH COMPANY3395 South Bannock StreetEnglewood, ColoradoTelephone: Sunset 9-3551TWX: ENGLEWOOD, COLO. 106EL PASO, TexasEARL LIPSCOMB ASSOCIATES720 North Stonton StreetKEystone2-7281HARTFORD, ConnecticutINSTRUMENT ASSOCIATES734 Asylum AvenueTelephone: CHopel 7-1 165HIGH POINT, North Corolino8lVlNS 8 CALDWELL1923 North Moon StreetTelephone: Hlgh Point 2-6873TWX: HIGH POINT NC 454

held posts with the Westinghouse Elec-tric Corporation in Metuchen, New Jer-sey. He served as Engineering SectionManager and was engaged in the designof color television receivers until Jan-uary 1956 when he was appointed Man-ager of TV Engineering. He served inthe latter capacity until he joined BRC.An active radio ham, Mr. Duyneis also a member of Tau Beta Pi, EtaKappa Nu, Sigma Chi and the Institute7f Radio Engineers.

JOHN P. VanDUYNE

HOUSTON 5, TexosEARL LIPSCOMB ASSOCIATESP. 0. Box 65733825 Richmond AvenueTelephone: MOhowk 7-2407HUNTSVILLE, AlobomaBlVlNS B CALDWELLTelephone: J Efferson 2-5733(Direct line to Atlonto)INDIANAPOLIS 20, ndionoCROSSLEY ASSOS., IN C5420 North College AvenueTelephone: C Lifford 1-9255TWX: IP 54510 s ANGELES, CalifornioVAN GROOS COMPANY21051 Costonso StreetPost Office Box 425

Woodland Hills ColifornioTelephone: Dlokond 0-3131TWX: CANOGA PARK 7034

R A D I O

ORLANDO, FloridaBlVlNS B CALDWELL1226 E. Colonial DriveTelephone: CHerry 1.1091

OTTAWA Ontario, ConodoBAYLY ENGINEERING, LTD.48 Sparks StreetTelephone: CEntrol 2-9821ROCHESTER 10, New YorkE. A. OSSMANN 8 ASSOC., I N C .830 Linden AvenueTelephone: LUdlow 6-4940TWX: RO 189SA N FRANCISCO, C alifornioVAN GROOS COMPANY1178 Lo s Altos AvenueLos Altos, ColifornioTelephone: WHitecliff 8-7266ST. PAUL 14;MinnesotaCROSSLEY ASSOC., INC .

842 Roymond AvenueTelephone: Mldwoy 6-7881TWX: ST P 1181

SYRACUSE, New YorkE. A. OSSMANN & ASSOC., INC.2363 J omes StreetTelephone: HEmpstead 7-8446TWX: SS 355TORONTO, Ontario, ConodaBAYLY ENGINEERING, LTD.Hunt StreetARL LIPSCOMB ASSOCIATESP 0. Box 7084Telephone: F leetwood 7.1881TWX: DL 411

Ajox, Ontario, ConodoTelephone: Aiax 118(Toronto) EMpire 2-3741

BOONTON- NEW JERSEY8

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