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X-952.77-11PREPRINT

--y^ x - '7 /..z IF3

AIRCRAFT MEASUREMENT OFRADIO FREQUENCY NOISE AT

121.5 MHz, 243 MHz AND 406 MHz(NASA-TM-X-712 8 3) AIFCn6FT MgASUBhMiST OF

1477-11290

, ADIC FFECUANCY NOISE AT 121.5 MHz, 243 MHzAiL 4C6 MikiZ (NASA) 8 P hC A02/MF A01

CSCI 17E UnciasG3/32 24194

RALPH E. TAYLORJAMES S. HILL

F

JANUARY 1977

1 7

^^ YJ1\y ^ 'J `J^/r

{. APR 1977

RECEIVEDNASA STI FACILITYINPUT BRANCH

--- GODDARD SPACE FLIGHT CENTERGREENBELT, MARYLAND

I

a_ e

X-952-77-11(PREPRINT)

AIRCRAFT MEASUREMENT OF

RADIO FREQUENCY NOISE AT

121.5 MHz, 243 MHz AND 406 MHz

Ralph E. TaylorJames S. Hill

January 1977

GODDAIU) SPACE FLIGHT CENTERGreenbelt, Maryland

This paper prepared for presentation at 2nd Symposium andTechnical Exhibition on: E'ectromagnetic Compatibility,Montreux (Switzerland), June 28-30, 1977.

i

CONTENTS

rPage

SUMMARY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . 1

AIRCRAFT INSTRUMENTATION . . . . . . . . . . . . . . . . . . 1

AIRCRAFT FLIGHT PROFILE . . . . . . . . . . . . . . . . . . . 2

AIRCRAFT SURVEY DATA MEASUREMENTS . . . . . . . . . . . . . 2

CONCLUSION. . . . . . . . . . . . . . . . . . . . . . . . . . . 3

ACKNOWLEDGMENT. . . . . . . . . . . . . . . . . . . . . . . 3

REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . . . . 4

ILLUSTRATIONS

Figure Page

1 Block Diagram, Noise Recording InstrumentationOn Aircraft . . . . . . . . . . . . . . . . . . . . . . . . 2

2 Aircraft Flight Path . . . . . . . . . . . . . . . . . . . . 3

TABLES

Table Page

1 Measured Antenna-Noise Temperature Over Eastern U. S.

Cities (25, 000 Feet Altitude) . . . . . . . . . . . . . . . . 4

IMECRDING

iii

J

AIRCRAFT MEASUREMENT OF RADIO FREQUENCY

NOISE AT 121.5 MHz, 243MHz AND 408MHz

Ralph E. Taylor

NASA Goddard Space Flight Center

Greenbelt. Maryland 20771 USA

James S. Hill

RCA Service Company

Springfield, Virginia 22151 USA

Summary

An airborne survey measurement of terrestrialradio-frequency noise over U. S. metropolitan areashas been made at 121. 5, 243 and 406 MHz with hori-zontal-polarization monopole antennas.

Flights were at 25, 000 feet altitude during theperiod from December 30 0 1976 to January 8, 1977.

Radio-noise measurements, expresst-ti in equiva-lent antenna-noise temperature, indicate a steady-background noise temperature of 572, 000 K, at 121.5MHz, during daylight over New York City. This datais helpful in compiling radio-noise temperature maps;in turn useful for designing sateUtte-aided,emergency-distress search and rescue communication systems.

Introduction

An airborne measurement of terrestrial radio-frequency (RF) noise at the emergency-distress,search and rescue (S&R) frequencies 121. 5, 243 and406 MHz was made over T:. S. urban and suburbanareas. The primary purpose of survey was to makeIn situ measurements of RF noise within the narrowS&R bands ( 121. 5 MHz t 25 kHz, 243. 0 MHz t 25 kHz,and 406. 05 MHz : 5o kHz) for compiling RF noisetemperature maps, in turn helpful for designing satel-lite-aided 5&R communication systems.

This is the second airborne flight survey of aseries conducted by the National Aeronautics andSpace Administration ( NASA), the first Airbornei:lertromaKnettc - Envirocmcnt Survev (AEF. S-1) beingconducted in 1975 (1). Although other airborne flightsover both urban and suburban areas have been re-

ported in the literature, e, g. (2)-(3), these reportedmeasurements are for different frequencies and RFbandy dths than those associated with the S&R fre-quency bands.

Ploussios (2) measurements (1966) at 226. 2,305.5 and 3c9.2 MHz were for a 1.2 MHz receiverbandwirlth, being much wider than the 15 kHz and 25kilt handAWth measurements at 1'21 . 5 and 243.0 MHz,

respectively. for this survey. Skomal (3) indiealesdifficulty in scaling measurements from one hand-width to other bandwidths because of uncertaintiesin the waveform periodicity of impulsive-type RFnoise from urban and suburban areas.

Aircraft instrumentation

A Cessna 340-11 aircraft was selectc4l b-causeof its capability for operation at an altitude of 25, 000feet.

A borizontal-polarization, quarter-wavelength,monopole whip antenna was used for each of the121. 5, 243 and 406 MHz frequency bands. The 121.5MHz antenna was mounted horizontally on the star-board side of the aircraft fuselage, between the rud-der and wing section. with the 243 MHz and 406 MHzantennas mounted on the opposite side of the fuselagespaced more than one wavelength apart at 243 MHz.No accurate information is available on the antennaradiation patterns; antenna-noise temperature valuesgiven are referenced to the antenna output terminal.

Electronics instrumentation was mounted Inequipment racks housed within the pressurized pas-senger cabin. Instrumentation for RF noise record-ing (Figure 1) included low -noise 121.5 and 243 ^IHzreceivers, two HP435A power meters. Techrite 444stripchart recorder and an onboard clock that pro-vided a local (EST) time reference. A thir receiverfor 406 MHz cbnafsted of a low-noise prenmplifterwith spectrum analyzer and 35 mm, continuous-filmscope camera.

All 3 receiver channels were calibrated, inflight, with an onboard, 0 to 20 dB range. reference-noise generator (Figure 1) with zero setting refer-enced t.; 290 degrees kelvin (K). A step attenuatorwith a range of 0 to 12 dB was inserted at the an-tenna output terminal ( Figure 1) to extend the tem-perature measuring range of both 121.5 and 243 MHzchannels.

1

J-1 -_ r-4 •ART J ^l r_ .

171 5 MN, TA t' O A5[ i.M,aPI 171 5 MM, IF MP

! I}MNII ^! PIECE WER MITE IRI0 17da 15.H1 aANOWIDTH _NUIbI

RE CONOIN,:

STRIP - III SMN,R[! LAOIS[ C(OCR CHA IIT

RE CORDER 741 MN,

741 MN, TA t-

N

O 454^M, +aP! 741 MN, II HPMI17 MM,i RF Cf IV[R TFR

M TfR

RANONIDTN

'[/ OI K

406 MNr TA OaP1 NY 4p[ SIN,

i7 MN,i SPCIXUM ® NOISi

ANAI VlfR I ['11011 ^iRaYN

75m uSCORF

Hf IF RE LACE CAME HANOIb!

I ,f NI BATOR I _

• NI)NII , .NIAI l ^ P[Il ANIIf DMUN11w11I AN II NNA

• ^ I,IK N,.I\I 1•HI AM . '1 .1 II I•

Figure 1. Block Diagram, Noise Recording Instrumenu[tlon (En Aircraft

The 121. 5 MHz receiver system noise figure was f = Ta LL

\\I I ^-- - 1/ + 11 dcg. k (1)

5, 0 dB, referenced to 290K, for zero d11 attenuator ^Ilsetting, resulting in a noise-temperature measure- where, F = Noise Figure of receiver, expressed asment range capabilit y of 2 90 to 1,400, OOOK. Simi- a power ratiolarIv, the 213 MHz receiver noise figure was 9, 0 4dB, corresponding to a range of 290 to 3,600,000K.

- Stripchart deflection, expressed as a power

N R ratio, from reading ti„ corresponding toAircraft Flight Profile zero setting of 290K from noise generator

Flight Path 1 followed a 200-mile, straight - line T. . 290K - Ambient temperature,course over the northeastern U. S, A. from Washing-ton, D. C. to Westchester, New York (Figure 2). Using equation (3-70) from (5), the equivalentBoth da y and night flights were made. Flights began antenna-noise temperature at the antenna witputDecember 30, 1976 and were completed .Januar y 3, terminal Is1977,

TA = L T deg% K (2)Flight Path 2 over the mid-western U.S.A. began

.January 6, 1977 and was completed .lanuary R, 1977, L = Attenuator loss, expressed in power, where>L^1,

Aircraft Survey Data Measurements i

- - — — — combining equation (1) and (2), 1lint& presented herein consists of lnsitu RF \ 1 1111

noise measurements at 121, 5 and 243, 0 Mitz, ex- TA = L T,, I FI n - 1I + IJ

dogs K. (3)pressed in equivalent antenna-noise temperature L \ f(deKs. Ki, referenced at the output terminal of a Fquation (3) was used for computing values in Tablehorizontall y-polarized, monopole antenna. Flight 1,,lata from 25, 000- feet altitude over the cities ofBaltimore, Marviand; Philadelphia, Pennsvlvania; The highest steady background temperntureN1 • w Castle, Delaware; and New York Clty are observed was 572, 1100K, at 121, 5 %1llz, during da y -Included, light hours over New York Citv, NYC (Table 1 ),

CNlservatlons at X43 MHz were al%%a y 9 less than ror-ItF noise measurements tit points 1-:i, Figure 1, responding values at 1:11, 5 MHz, ,luring ,hn light

reler • neell W the onimn(rd colllhnoled noise genrratnr, hours over the villa., geni-nilly In keeping with Jhare rxpressrll by till nbs,llule 11 . 111p1 • 111[1111e e,lunll(In servrlllml. re1Nr11e,1 h( 11(lualos C.!) and M. iwll CO.from (4) as, Furtherfnor•, too • N1'C observation ih I. dli greater.

2

l-

•

1 —44t

1 1 't—42—42 GI 1 1

I i—FLIGHT

,1 Lakv Mich gan I- -4' 1

1 PATH 11 Nvwvu,k 1

W1

—I i 1^^

II

CHICAGO IL' I1 WESTCHESTER,^' \ 1

N Y 4. rFLIGHT 1 L r 1 pv.,n Ii JPATH 2 I I --

, _

-- I 1 1 On,o 1 1 1 New Je,wy

II.- MJ,1 1 ENROUTE

y1Jn11 / i

IIndJna weuII III,nO, ^ 1

1 ty,1SmNGTnN DCI Vr nee4

\I 1 ^ \ AUnn,ci

i — t„ 1 1 1 Omar

^I--- — I 1I

1 1 11 1I I I 1

I, I t I t1

1 1 1 \90 88 86 84 82 Bo 78 76 74

LONGITUDE WEST

Figure 2, Aircraft Flight Path

at 121, 5 MHz, than Baltimore or Philadelphia,during da y light, agreeing with Ploussios (2),

Nighttime observations were alwa ys less thandaylight values by G. 3 to 10,6 dB, at 121. 5 MHz, forNYC, Philadelphia and Baltimore. however, night-time observations at 243 MHz show an unexpected4.3 to 5. 2 dB Increase in temperature compared to121.5 MHz nighttime observations for the same cities.

The data measurements exhibit good repeatabilityas evidenced by the same value of 572,000K beingmeasured on two different da ys over NYC.

Observations over the New Castle, Delawarearea indicate temperatures as low as 2600K and1600K, respectively, for 121, 5 and 243 fait. at night.These low values Indicate the following:

1. Approximately 24 dB increase in steady-background, terrestrial. RF noise level

comparing "noisy" daytime observations to"quiet" nighttime levels, for the worst Case.

2. Low elect romagnotic Interference (FM1)environment onboard the test aircraft,

Higher levels of "discrete" RF noise were foundto be present above the steady background level overthe major r! * ies, frequently saturating the noise-

temperature measuring equipment at both 121, 5 and243 MHz.

Sufficient time has not been available to reduceand report data from Flight Path 2, nor 406 MHzdata from Flight Path 1. These measurements shouldbe the subject of a later paper,

conclusion

An airborne measurement surve y has been re-ported for RF noise at 121, 5 and 243 %1Hz for major,northeastern 1'. S. A. cities. Observations of steady-background, RF noise Ictels during daylight hourswere alwa y s greater at 121 . 5 MHz than 243 Mftz,In keeping with observntions reported by Ploussios(2) and Skomnl (3).

Data measurements exhlbit good repeautbillh.Approximately a 24 dB increase in steady-background.RF noise level was observed comparing "noisy" day-time observations to "quiet" nighttime levels, forthe worst case.

Acknowledgment

The authors wish to thank the following person-nel at the RCA Service Company, Springfield, VA.22151, USA: Messrs. John Nistnes and RichardBolles for obtaining (late measurements in the testaircraft, and fir. James Connswsy for his sugges-tions,

Measured Antenna -Noise Temperature Over

--- --

Table 1

Eastern 1'. S. Cities (25,(100 Feet Altitude)

T Tempe nature-dogs, Kelvin (KI

- —C ityn I^tc•

FS

1'51.5 AI HZ -43 Milt^ Time

Philadelphia 3 Jan. 1977 1525 1:19,Onu 7o,^uu

(Div)

3 Jan. 1977 2158i

71,000 I 55,'400

(Night)

Baltimore 3 Jan, 1977 172 0 143 , 200 3.1, 500

(Day)

3 Jan. 1977 2234 12,500 34,500(Nltthtl

New York City 31 Dec. 1976 1051 572,000 358,500

(Day)

3 Jan, 1177 1605

(Do v)

2172,000 283,500

:1 Jan. 1977 2125 135,300 453,000

(Night)

New Castle 3 Jan. 1977 2204 8,500 12,500

3 Jan, 1977 21215 2,600 l,r,n0(NightI

• ,astern Standartl Time (lira. — Mina. )

I

References

1. Tavlor, Ralph E. and James S. Iilll:Airlborne F.leetromagnctic Environment

Survey of U. S. A. Urban Areas, IEEE 1976International Symposium on ElectromagneticCompatibility (EMC), session 2H, July 13-15,1976, Washington, D. C.

2. Ploussios, G.: Noise Temperature of AirborneAntennas at UHF. Technical Note 1966-59,Lincoln Laborntnrv, MIT, Lexington, Sloss.December f,, 1966.

3. Aomal, F. N.: Distribution and FrequencyDependence of Incidental Man-Made HF/VHFNoise in Metropolitan Areas, IE:EE Transactionson Electromagnetic Compatibility, %'ol. FMC-11,No. 2, pp. 66-75, \la y 1969.

4, Hewlett-Packard Company: Noise Figure Primer,Application Note 57, .June 22, 196,2,

5. Berkowitz, Ii. S. : Modern ga0ar Analysis,Evaluation and Svstem Design. John Wllev &Sons, Inc. , 1967.

4