JOURNAL OF RESEARCH of the National Bureau of Standards-D. Radio Propagation Vol. 66D, No.2, March- April 1962 Fading Characteristics Observed on a High-Frequency Auroral Radio Path J. W. Koehl a nd H. E. Petrie Contribution from Central Radio Prop a gation Laboratory, National Burea u of Sta ndards, Boulder, Colo.
(R eceived June 22, H)61 ; rcyiscd September 14, 1961)
Obsen·ations of f,.d ing chamcLerisL ics of h igh-frequency sig na,ls have been carried ou t on a long path (4,470 ki lometer,) pass i ll ' ~ Llnoug h the a uroral zone. SLaL istics were obLain ed on fading rate, shor t-Lern1. carrier ampliLud e flu ctuaL io ns, and fad e duraLio ns. Fad in ~ raLes higher than 20 c:vcles per second were observed for a s mall percenLage of Lhe time at each of the t hree carrier frequencies u sed, >Lnd show only a minor d itlrnalLrend, wiLh lhe maxi mum usually occurring during t he early morning h ours. Rayleigh di sLribuLions of carrier envelope ampli Lude were obtained for many of the observaL ions; however, fading depLh was normally reduced during periods of rapid fading.
1. Introduction 2. Experimental Facilities Th e ch aracteristics of carrier envelope ampliLude Observations were carried out over a paLh from flucLuations, or fading, musL be co nsidered in at Barro\ , Alaska, to Boulder, Colo., during 1959 and lempting to predict Lhe perrormance of radi o systems. 1960, at frequencies of 9.9475 M c/s, 14.688 M c/s, and Fa.dillg on high-Jrequency io nospheric links may be 19.247 M c/s. The great circle distance is 4,470 km. caused by changes in absorpLion of Lhe waves, by Figme 1 shows the geographic location of the path interference between two or more componenL of the relaLive to the ul1cli Lm bed auroral zone. waves arriving by different paLh or by changes in polarization of t he downcoming waves. Absorption fading is usually much slower than Li lC oLher types. Movement oJ ionosp heric Jayers and irreg ularities in the ionosphere cause changes in phase path - APPROXIMATE ZONE OF MAXIMUM AURORAL ACTIVITY lengths and in the state of polariza tion of the mulLi path components, accounting for the more rapid III amplitude flu ctuations. A very rapid fading, some times referred to as "fl uLl er" facli ng, has been ob served lor m any years on Jligh-frequency paths passing through or ncar the auroral zone. ~everal investigaLors [Rice, 1944, 1945, 1948, 1958 ; .\1cKicol, 1949 ; Norton, Vogler, Mansfield, and Sbort, 1955; Norton, Rice, Janes, and Bar·sis , 1955] have made theoretical analyses of carrier fading, considering the problem on the basis of envelope behavior for narrow-band Gaussian noise models, with or without steady components. Ob servations of certain short-term high-frequency prop agaLion characteristics h ave been performed by many workers in the field, for example, Grisdale, :Morris, and Palmer [1957], Aggarwal [1959], and Yeh and Vill ard [1960] . The purpose of the obser vations reported in this paper is to provide some ad ditional statistical information on short-term fading cbaracteristics for signals propagated on a long pa.th throug h auroral regions. Resul ts of the observ8 tions 140' 130' are presented in several different forms; the intent is to give as clear a picture as possible of the observed 120' 11 0' statistical beh8vior of carrier envelope fading on the path. FIG lIRE 1. Geographic location of transmitter and receiver 1 Present address: Ball Brothers Research Corp., BOUlder, Colo. stations.
G1948 3-62--3 159 2.1. Transmitting and Receiving Stations and displays on decade counters the percentage of time the carrier envelope voltage exceeds threshold The transmitting station was set up at the camp levels set at 5 db intervals. The fade duration of the Arctic Research Laboratory, Barrow, Alaska, analyzer displays on decade counters the percentage with three 3 kw transmitters. All transmitters of time the carrier envelope fades to and remains had precise carrier frequency control, with stability below preset levels for various minimum durations of better than one part in 108 per day. The trans of fades. Fade durations from 2.5 to 500 msec were mitters were operated with unmodulated steady analyzed in this manner. Fading rates at different carrier for these observations. carrier levels relative to tbe median and for different The receiving station was set up at the National durations of fades are also obtained with this Bureau of Standards Table Mesa field site near equipment. Boulder, Colo. Receiving equipment consisted of high quality communication type receivers with external heterodyne oscillators. The oscillator sta 3 . Carrier Envelope Fading Characteristics bility was within one part in 10 8 per day. Modifi cations were made in the receivers to provide a 1-msec 3.1. Theoretical Curves time constant in the automatic gain control (AGO) circuits. An external envelope detector with a It is of interest to examine the behavior of fading 2-msec time constant was used to provide the AGe signals based on assumed theoretical model of the voltage for each receiver and to supply an envelope propagating medium. The theoretical curves pre voltage for recording purposes. An .intermediate sented here have been derived by reference to the frequency tra~slated down frOl~l the car!'ler freque~cy considerable amount of work by S. O. Rice [1958]. was also avaIlable for operatmg contmuous fadll1g He has assumed that the envelope voltage of the rate recording equipment. A twelve-second time received radio wave varies in the same manner as constant was used in the AGC circuit when the the envelope of narrow-band Gaussian noise (Ray receivers were used for continuous fading rate record leigh distributed) having a normal-law power spec ing. The receiving anten.nas at th.e Table Mesa .site trum centered on the transmitter frequency. were half-wavelength hOl'lzontal dIpoles at a hmght The probability that the duration of a fade equals of one wavelength above the ground. or exceeds a time T seconds in length for a given crossing level has been developed by Rice [1958]. 2 .2 . Data Recording and Analysis Equipment The following expression has been applied to his results to obtain a family of curves, figure 2, showing a . Fading Ra te Recorder the distribution of carrier envelope amplitudes for various minimum durations of fades: Each receiver had an associated fading rate recorder which operated continuously except for short periods when recordings were being made for P (D r, R)= P (DrIR) P (R ) other fading analysis. The fading rate instruments [Koch, Harding, and Ja,nsen, 1960] record on paper charts the average number of times per second the 0.0 I instantaneous carrier envelope voltage crosses the 0.02 1 k---- TN m=500 six-second average canier envelope level with a \ ~ ~ 0.05 "- 1\ \\ 300 positive slope. Fading rates recorded by this inst!·u ~ i= recorded on magnetic tape for later analysis. The ~ ~ 0 80.0 FM recording technique was employed, wherein the ~ a) 95.0 detector output voltages modulate FM sub carriers 99.0 99.9 99.9 9 in the tape recording equipment. - 30 -20 -10 +10 An amplitude distribution analyzer and fade dura db RELATIVE TO CARRIER ENVE LOPE WEDIAN LEVE L tion analyzer were used with the tape reproducif!.g equipment to obtain ~tatis.tics on the fine ~ram FIGURE 2. Theoretical distributions of carrier envelope fluctuations of the fadmg sIgnals. The amplItude amplitude for various minimum fade durations. distribu tion analyzer samples the carrier envelope T is minimum duration of fades in milliseconds. N m is average number of time~ per second carrier en velope voltage passes downward across median ]ovel; voltage 1,000 times per second with 50 p.sec pulses, narrow·band Gaussian rancl om noise model with normal-law power spectrum. 160 where j (Il) = probability that instantaneoLls carrier L envelope voltage is equal to 01' less tban -7.4db R for a Rayleigh fading signal; + 4.5db b P (D T / H) = conditional probability that a fade has a -13.5db ...... '\ duration equal to or exceeding T, given \ that the crossing level is R; - 19.4 db ~ \ ~ ~ P ( D ~I" H) = probability that the carrier envelope volt o~~ ..,w 0.1 \ ,,> age fades to and r emains below the level ~oW R for a time duration equal to or exceed ~w...J "",,,,~ ~'" 0.05 ing T. ZOu; ",,,,,,,w~~ \ «"U ",0 W'h en th e mll1unum fade duration is such that all 0.02 U u >",ow '" fades are included, the distribution becomes "'z~ \ ~ Rayleigh. x 0.01 \ 2.5 10 25 50 100 250 500 X rJ- Figure 3 is a plot of thcoretical average fading m rates versus crossing levels relative to the median FADE DURATION. m sec carrier envelope level, using th e expr ession [Rice, FIGURE 4. Theoretical Jading rale versus minimum Jade 1958] : dW'ation Jar indicated cctlTiel' levels relative to median carrier envelope level. ]\'". is average number of l.imcs per seco nd ca rri er CI1\'c lopc \Toltagc passes down. ward across median level; narrow-band Gaussian random noise model. where 3 .2. O bserved Fading Rates Nn= aver age fading raLe (all fad es) at level R ; Average fading raLe observations have been car Nm=average fading rate (all Jades) at m edian level; ried ou t during t he period from August 1959 tln'ough En= carrier envelope voltage at level R; January 1960 on Lhe Barrow Lo Boulder paLh. The E m=m.edia n carrier envelope voltage. recordings have been scaled for hourly maximum and 10-l11in fading rates. Figure 4 shows theoretical Jading rales versus Figures 5 and 6 are plots of diurnal variations of minimum. fade durations for variou s crossing levels, fading rates for the monLhs of October 1959 and based 011 the assumption that, 20 N TR = P (D1' /R)Nn 19247 kc/s where 15 10% Nz·n=a\Terage fading rate for minimuill fade du 10 ration T at crossing level R. 50% 2.0 90% 0 00 02 04 06 16 20 22 24 LOCAL TI ME AT RECEIVER (105·WI 1.0 = 20 ~ «~ ./ 14688 kc/s ~ -" -;; ./ 15 0.5 --" C>z ./ \ w 0 ~ ~ .., 10 C> ;}. ./ « '" ~ ~ 10% ~ z «> > '" ~ 0.2 / l <5 ~ 50% ~ ~ 0 z 90% 0 « ,.i§ 08 10 12 14 16 18 20 22 24 ~ 0.1 \ LOCAL TIME AT RECEIVER 1105· wi 20 15 10% 10 50% 0.02 90% 0.01 02 04 06 08 10 12 14 16 18 20 22 24 -20 - 15 - 10 -5 +5 +10 LOCAL TIME AT RECEIVER 1105· WI CROSSI NG LEVEL IN db RELATIVE TO CARRIER ENVELOPE MEOIAN LEVEL FJG URE 5. Diurnal variations of houdy maximum fading rates, October 1959. FIG eRE 3. Theoretical fading rate versus crossing level for Hourly maximum fad ing rates are exceeded for percentage of time indicated by na1Tow-band Gaussian noise model. cur ve parameters. 161 25 0 192 4 7 kc/s i' '\ 20 ~, 10% IG 15 ' 'tI-19., 247.0 kc/s 50% - 10 , ...... , . -S 12 90% "-. ~ ~ I ~ I\.' 0 I 00 02 04 06 08 10 12 14 16 18 20 22 24 ~." \"" ~ 9947 . 5kC/s LOCAL TIME AT RECt:IVER (lOSo wI \ , ., 25 14688,0 kc"l5 ~ \ , 20 10% '\ ". u ...... " ' 1-.. 15 .,' -- i--t=::f--; "'t-- 50% 10 o t-= t---==: OD! 0.05 0.1 0.2 0.5 I 2 5 10 20 40 60 80 90 95 98 99 99.5 99.9 99.99 PERCE NTJ\GE llF TI ME HOURLY MAX I MUM FADING RATES EXCEED ORD INAT E FIGURE 7. D'istriblltions of ho urly maximum fading rates, 02 04 06 08 10 12 14 16 18 20 22 24 October 1959. LOCAL TI ME AT RECE IVER (105° w ) 9.9475 ~V l c/s-420 I1l' 14.688 M c/s-497 h l' 19.247 1\1c/s-318 hl' 20 25 , - 10% ...... 15 ~ - ~~ - " , - 50% ~ , 10 20 p:.:: ~..".. - - 146BB_Okc/s ~ - - \" '--_ 90% -\ . - \ '5 15 02 04 06 08 10 12 14 16 18 20 22 24 I- \\r,. . "'75kC/S I \ LOC AL TIME AT RECEIVER (105 0 w ) l- , . I- \ . - 19247.0 kcl5--\ \ I- , .. FIGURE \ \ 6. Diurnal variations oj houdy maximwn Jad'ing rates, ~ 10 January 1960. I- , ..\ - ,\ ]Tonrly maximUlll fading rates arc exceeded for percentage of time indicated by I- , - curve parameters. I- ~ - I- ,~ 0 , - l- - January 1960, and show the 10,50, and 90 perce ntile I- - values of hourly maximum fading- rates. It appears I- t;:: k::k - I- l-~ -~ that there is a tendency for the high er fading rates o 001 0.05 0_1 02 0.5 I 2 5 10 20 40 60 80 T90 95 98 99 99.5 99.9 99.99 to occur during the early morning hours. Figures PERCE NTAGE OF TIME HOU RLY MAXIMUM FA DI NG RATES EXCEED ORDI NAT E 7 and 8 are distributions of houdy maxim.um. Jading rates for the months of October 1959 and Januan' FIGuRE 8. Distributions oj hOlldy maximum fading Tates, 1960. Distributions of 10-min median fading' rates Janlla1'y 1960. 9.947.\ :l1c/s- 649 hl' for the sam.e months are shown on figures 9 and 10. 14.688 .\1c/s-586 hr From th e data obtained, it was found that fading 19.247 NIe/s-307 hl' rates gradually incr eased from October to J anuary, with the lowcst fading rates being observed in values in the order of 6 to 15 cis within a fow minutes October, and the highest fading rates being observed time. Change from the fast fading rates to slow in J anuary. fading rates occurs just as rapidly. An attempt was made to determine if there were any characteristic changes in fading rates immedi 3.3. Carrier Envelope Amplitude Distributions ately preceding or following major magnetic fluc tuations. The results of the analysis did not show Typical amplitude distribution curves for the an:)' significan t factor in this regard; however, fading received carrier envelope voltages are plotted on rates were generally high er on disturbed days figures 13 and 14. It will be noted that several of t han on quiet days, as shown by comparing figures the curves approach a Rayleigh distribution for the 11 and 12 . fading carrier envelope. vVhen a R ayleigh distribu The received median signal strengths fLre usually tion is obtained, the average fading rate is usually lowered in value by 10 to 20 db when a period of fairly low, although there are exceptions. During fast fading occurs, although this is not always the fast fading conditions, associated with auroral case. Fading rates often change from 1 to 2 cis to activity, the depth of fading is normally somewhat 162 20 >< w a :z ~ t : : : ; : : : : : : :d 16 1- .,~. 00 04 08 12 16 20 24 192 41 0 kcls~ LOCAL TIME AT RECEIVER (lOS· wi - 1 i' - 110 '\ \ '5 I 2 1\ '\0 -120 30 \'\ ., '\, ., \ 8 -140 20 1'. , '- 'I r, •.1 r, o~ 9941.5 kc/s - 160 10 4 1 4688 .0 kC/s ~ ~\ r"-. 1'-. ,~, '\ '"- ~ ::,.. '-... .".-- ~ \ I '" ...... --~ f""'::: '$ .... J -- ~ ~ , r-r- . .<:> -180 0 0 • 00 04 08 12 16 20 24 0.01 0.050.10.2 0.5 I 2 5 10 20 40 60 80 90 95 98 99 995 999 99.99 :t: PE RCENT AGE Of TI ME 10- MINUTE MEDIAN FADING RATES EXCEED ORDI NATf f- LOCAL TIME AT RECEIVER 1105· wi ~ z <..) w'" -110 f- w FIGURE 9. Distrib1,/1:ons of 10-min median fading mtes, '"U"> f- -120 14688 kc/s 30 - - -1 60 10 - -. '"---_/" - 00.01 0.050102 0.5 I 2 5 10 20 40 60 eo 90 95 98 99995 99.9 9999 - 180 L-,---,_-,---'.---':::L....--'---'---'--L--'---'---'24 0 PERCENTAGE Of TIME 10 - MINUTE MEDIAN fADI NG RATES EXCEED ORDINATE 00 04 08 12 16 20 LOCAL TI ME AT RECEIVER (105 · wi FIGUR E 10 . Distl'ibutions of lO-min median fad'ing rates, Januw'Y 1960. FIGL;RE 11 . Diurnal vW'iatio ns of signal strength, fading rates. 9.9475 M r/s- 3935 JO- mjn sa mples and Barrow, Alaska, magnetic activ'ity index for quwt day, 14.688 Mc/s-3435 lO- min samples December 10, ]959 19.247 MC/S-1836 lO- min samples tion has been found to be quite useful as an aid in reduced ' til is effect is indicated by the curvature at predicting performance. of c~rtain co~mun~ca tion tbe level portions of some of the distribution low ~r systems. As noted prevlOusly 111 co nnectlOn wlth the curves. A statistical model of a constant vector am plitude distribution curves, when th? c.b aracter plus a Rayleigh distributed vector as described by istic auroral-type fast fading occurs, the £admg depth [195~], Norton, Vogler, Mansfield, a,nd Short will is normally reduced, especially for the ~bort f.ad e produce shallow fading when the power ll1 tbe durations, from that obtained with R ayleIgh fadll1g. co nstant vector is several ti.m es greater than the However, one sample was obtained, figure 16 , power in t he Rayleigh distributed co mponent. which had the fairly fast fading rate of 6 cis and maintained a nearly Raylei.gh distribu tion for the 3.4. Di stributions of Envelope Amplitudes for Various very short mi.nimum fade durations. Minimum Durations of Fades 3.5. Observed Fading Rates at Various Crossing The distributions of canicl' envelope amplitudes for Levels Versus Minimum Duration of Fades various minimum fade dura,tions, figures 15 through 19 reflect the stfttistics of the depth of fading for Some of the fade duration data obtained has been ce;'tRin minimum fade lengths. This type of infonna- plotted so as to show the observed fading rates as a I~ 163 >< w 99,9 9 co z • 99.9• ':: ' I ; : ~ ~ : : : : : ; 99,9, r ' "'\ ' :()() 04 08 '2 'S 20 24 99.9 :~ 1\ \ LOCAL TIME AT RECE'VER ( 'OS OWI 99.8 1,\ 0 -"" '\ \ - '20 \'\ 30 99,S ". ...J 99 .0 ~ ~'\ \ ::' ,,~ - '40 20 ~ 98.0 -"'. .~"- ~ 95.0 ,"'~ -,so ~ 90.0 ~~'\ '0 ::IE 80.0 \\"'" . "- ~ ~ , ~ -'-; " "_ \ ~, ~ " ~ 60.0 ~ ~ ' '- '1'. or >- - '80 <.0 0 ~ z ()() 04 08 ~ w '2 'S 20 24 u j ::: ~ LOCAL TIME AT RECE'VER ( 'OSO WI .... _ 5.0 >- 1.0 ~ -' 30 " ..:::" --' 25 : 0.1 -'" ~ 0.0 I <.0 150 140 130 - 120 -110 -100 -90 in - '40 '"z 20 Co RECEIVED CARRI ER ENVELOPE LEVEL , db w ~ ~ > r ... § --" \ z FIGU RE 13, Amplitude distTibutions of can'ier envelope- - ISO 'v"",- .. 9.9475 Mc/s. '" 10 i;j z '- ...." '" \ I Sampling period 200 sec .. '4S88 kc/s '" Low pass bandwidth of system 312 cis (-6 db) 0 w " R ay l e i ~ h distribution is straight li ne with slope or m in'Js onc, -IGO 0~ A- Sept. 23, 1959;0353 LTR(105° W ) 8 cis average fa ding ratc '" 0 or 00 B- Oct. 2, 1959; 2021 L T R (105° W) 1..1 cis average facling rate ~ 04 08 '2 'S 20 24 => O- Oct. 2, 1959; 1933 LTR (' 05° W) 1 cis average facl in g rate co LOCAL T'ME or AT RECE'VER ('OSO WI D - Oct. 2, 19.59; 2217 L'l'R(105° W ) 6 cis average fading ratc - '40 20 E-Sept. 23 , 1959; 0443 LTR(l05° W ) 12 cis average fad ing ratc 99.99 - 'SO '0 99,98 < '9247 kc/s 1\\ \:A ~ 99.95 s \ - '80 99.9 \ \'i 0 00 ~ E \ O 04 08 '2 IS 20 24 99.8 c..\\ \ LOCAL TIME AT RECE'VER ('OSO WI \'. 99.5 0" 1,\ FIGURE] 2 . D'iu1'nal vaTiations oJ signal sl1'ength, fading m tes, oJ 99.0 \ \\ ::' -"" and Ban'ow, Alaska magnetic actwtty mdex fOT distuTbed day. " ° ~ 98.0 "''.~ December 14, 195!J 95.0 ~ ~ i,~ ~ 90.0 I" function of crossing levels and minimum duration of :::II! 80.0 I\'t "'-0 fades; figures 20 and 21 ar e examples of this informa " '\ "'\. ~ 60.0 . \.'- ."" ~ It t ion, is interesting to note that the maximum 40.0 z crossing rate occurs near the median carrier level 20.0 , in all cases for short duration fades. At levels a few ~ 5.0 decibels above the median tbe crossing rate curves 1.0 ~ " 0.1 ~ "' 0.0 I are fairly fl at, indicating that only r elatively long ·150 -1 40 -130 -1 20 - 11 0 -100 - 90 duration fades occur at these levels, while at the lower RECEIVE D CA RRI ER ENVEL OP E l EVEl 1 dbw levels most of the fades are of short duration. FIGURE 14. Amplitude distributions of carrier envelope- 19.247 Mc/s . 4 . Summary Sampling pcriod 200 sec Loss pass band wiclth of system 312 cis (-6 db) Hayleigb distribution is straight line with slope of mi nus one. Statistical information has been obtained on A-Sept. 15, J959; 1337 LTR (105° \1') 1 cis avcrage fad ing rate certain experimentally observed fading characteristics B-Scpt. 15. 1959; 0936 L'1' R (105° W ) 6 cis average facling rate O- -Sept. 15, 1959; 1142 L'I'R (10.1 0 \1') 10 cis average fading rate of high-frequency continuous wave signals propa D- Oct, 2, 1959; 1933 L'1'1< (1050 W ) 1 cis avcrage fading rate gated over a long path t hrough auroral regions. E- Nov. 20 , 19,19; 1544 L '1' R (105 0 \1') 2 cis average fading rate Fadi.ng rates in the order of 20 cis have been observed for short periods at all of the obser ving frequencies. I n most instances the received median canier fading rates generally increased from October 1959 envelope level drop 10 to 20 db when a period of to J anuary 1960. However, the au tumnal equinoctial fast fading set.s in. Fading n,tes were generally period in 1959 was unusually quiet from an auroral higher on magnetically disturbed days than on quiet di sturbance standpoint and should not be co nsidered days. It was found for these observations that typical. 164 0.0 I 0.0 I \ \ \ , , \ , \ \ \ .~ ~ : , , 002 0.0 , \ \ , soo \ \ ~l'" OINI.U. OURATIO N " b-- \ ~ \ \ , -100 FADES, 5:~ msec _ 25 \ 1 : :S250 O.O~ :.; 0.0 , nJ. \ \ SO _\~\~ \ - ~~~roo "~ -r--- __ " MIN IMUM DURATIO N Of 10 __ 'I \ I I 0. 1 0. 1 - FADES, msec IO~:~ \ \/, --r-- 0.2 02 \ e :~: \: : i ' . '-.... .~ \ I ~ - '\ \ I \1 \ r. 0.' ~ ~ ~ 0. 5 " - ~ . \ \ ':I- - \- ,-I- ~\r. I, \ • 1.0 \ \ , I I ~\, '\ ~,- ' .0 '\.'\.\ \ "'o>~ i:1 :: '.0 \\ \\ \ ~ j ~~t" \ 'n tO,O \\ \\ ~ ~ 20.0 ~\\ §:\' :o~ '< 40.0 -\ 0 ~\ ~~ ... ~ 60.0 -_.-p.;~ ~ ~ ~ 80.0 ,,'- - 95.0 ~~-1---= 99.0 i==- 99.9 99.99 9 - -30 ~ 20 -to 0 t 10 -30 -20 -10 0 '10 db RElAriVE TO CARRIER ENVELOPE MEDIAN LEV EL db RELATIVE TO CARRIER ENVELOPE MEDIAN LE VE L FIG UR E 15. Dtstrib1dions oj carrier envelope amplitude .for FIGURE 17. Distributions oj can'iel' envelope amplitude for various minimum Jade dumtions. vaTious minimwn fade dumtions. Sampling period 200 sec Sam pling period 200 sec Low pass bandwidth of system 312 cis (-6 db) Low pass bandwidth of systcm3J2 cis (-6 db) Median carrier to noise ra tio 38.0 db Median carrier-to-noise ratio 27.5 db A vcrage fading rate 1.5 cis Average fading rate 12 cis 9.94751!.,[c/s, Octoberl.j 1959. 1933 L'l'R (105° w ) 14.688 Mcls, December 23. 1959: 1435 L'T' ll (105° \\') 0.0 I \ , , , \ 002 0.0 I \ \ \ \ \ \ I \ I I I \ \ 0.02 I I 25 \ :I' L 250OOj MINI MUM DUR AT ION OF \ \ \ \ \ ~ _ IO ------.l\ I I ' 100 fADES, m sec - 250'" MINl tot UM DURATION Of - \ } \ \ \ I \ 50 "-f! . .. ~ 100 FADES, msec l----'.;- \ I I I "--...... \ \ ;;:~ \ \ ,,-~ ~;-'" \ I .'\.\ \ \ ., \ I ~j\ '. \ \ I . ~\ "r, \ \ i\ \ \ '\ ~\ \ ~ ~\\ . ~ \ -~l\ . ~ , ~ ~ 3 5.0 ~5~ '\~ ~ ~ ~ 10.0 ~. \ ~~ : ~ g200 ~\\ '" -~ . .... ~ ~ 400 ~:~60 . 0 ~ . ~ ~ ;3 c 80.0 ~CD 99.0 95.0 99,9 99.0 99.99 - 20 -10 99.9 -" '10 9 db REL ATIVE TO CARRIER ENVELOP E MEDIA N LEVEl '" -30 -20 · 10 '10 db REL ATIV E TO CARRIER ENVELOPE MEDIAN LEVEL FIGURE 18. DistTibutions of can'ieT envelope ampWude for FIGURE 16. Distributions of carrier envelope amplitude for various minimum fade dt,rations. vanous mininmm fade dumtions. Sampling period 200 sec Low pass bandwidth of system 312 cis (-6 db) Sampling period 200 sec Median carricr-to-noisc ratio 32.0 db Low pass ban dwidth of system 312 cis (-6 db) A verage fading ratc 1 cis M edian c,uTier-to-noise ratio 32 db 19.247 Mcls, October 2, 1959 ; 1933 LTR (1050 W ) A I'crage fading mte 6 cis 9.9475 Mcls, October 2, 1959; 2217 L'l'R (105° W) time durations, is normally somewhat Ie s for the Fading r ates exceeded for small percentages of the auroral-type fast fading than for slow fading. This time were highest at the higher of the three carrier would seem to indicate Lhe presence of a relatively frequencies observed; however, for fading rates sLeady component and a weaker fast-fluctuating exceeded for large percentages of the time, the componen t when fast fading conditions exist. lowest carrier frequency exhibited the highest fading A Rayleigh distribution of carrier envelope ampli rate. tude was observed for a few of the periods, usually The depth of carrier envelope Jading, as deduced when the fading rates were fairly low. Most of the from the amplitude distribution measurements for time, however, the carrier envelope amplitudes all fades and for fades exceeding various minimum departed considerably from a Rayleigh distribution. 165 0.0 I lU.U \ , , I I , SOD 0.0 I I, ""- :.-1--"0 z: 10.0 I--- 1 100 :;j f-- ~~b I · MI NIMUM DURATION OF l~~25--: \ ~ ~V I I-- FADES, msec IO~ 1\ '"'-' J{ \ , 1;'; 5.0 + 2.5 db 25~O I , "'", \ I '"0. 0 ·1...... :.. 1, .\ \ 1\ I '"> "-"" '" "'''' T7. 5 d b , \\ ,, \ '\ \1\ ~~~a 2.0 r, ""-''''I.£.. ~. 5db \ '\. 5 . References \ '\. \ Aggar w3.l , Ie. K ., Statistical analysis of fading on short-wave \ \ transmissions, J. Inst. Tel. E ngl's. (New Delhi) 5, No.4, \ 230- 237 (Sept. 1959). ~;~ I~ ,\ Grisdale, G. L., J . G. Morris, and D. S. Palmer, Fading of - long-distance radio signals and a comparison of space and - 11.5 db polorization-diversity reception in t he 6- 18 Mc/s range, Proc. Inst. Elec. Engrs. 1MB, No. 13, 39- 51 (J an. 1957). '\. \ \ Koch , J. ' V., YV . B. I-larding, and R. J . Jansen, Fading rate '\ \ \ \ recorder for p ropagation r esear ch, E lectronics 32, No. 51, \ 78- 80 (Dec. ] 8, 1960). \ \ McNicol, R. YV. E., The fading of radio waves of medium and high frequencies, Pl'Oc. lust. Elec. Engrs. pt. III 96, \ \ \ \ No. 44, 517- 524 (Nov. 1949). 0.1 2.5 10 25 50 100 250 500 Norton, K . A., P . L. Rice, H. B. Janes, and A. P. Barsis, FADE DU RATI ON, m sec The rate of fading in prop agation through a turbulent atmosphere, Pl'Oc. I.R.E. 43, No. 10, 1341- 1353 (Oct. FIGURE 20. Fadmg rate versus minimum fade durations for 1955). va1-ious carrier levels Te lative to median caTTier envelope level. Norton, K . A., L. E . Vogler, W. V. Mansfield , and P. J. Sampling period 200 sec Short, The probability distribution of the amplitude of a Low pass bandwidth of system 312 cis (-6db) constant vector plus a Rayleigh-distributed vector, Proc. Median carrier-to-noise ratio 34 db I.R.E. 43, No. 10, 1354- 1361 (Oct. 1955). 9.9475 Mc/s, September 23, 1959; 0443 LTR (105° W ) Rice, S. 0., Mathematical analysis of random noise, pts. I & II, Bell System Tech. J . 23, No.3, 282- 332 (July 1944). Rice, S. 0., Mathem atical analysis of random noise, pts. III The experimental study reported herein was & IV, Bell System Tech. J . 24, No.1, 46- 156 (Jan. 1945). sponsored by the U.S. Ail' Force Wrigh t Air Develop Rice, S. 0 ., Statistical properties of a sine wave plus random m ent Division, Wrigh t-Patterson Air Force Base, noise, Bell System T ech. J. 27, No.1, 109- 157 (Jan. 1948). Ohio_ T he assistance of the Arctic Research Rice, S. 0., Distribution of the duration of fades in radio transmission: Gaussian noise model, Bell System Tech. J. Laboratory, Office of Naval Research, Point Barrow, 37, No.3, 581- 635 (May 1958). Alaska is gratefully acknowledged; Max Brewer, Yeh, K . C., and O. G. Vill ard, Jr., Fading and attenuation of Director, and other personnel of that laboratory high-frequency radio waves propagated over long p ath s have provided logistics and housing for equipment crossing the auroral, temperate, and equatorial zones, installation and operation at Barrow. Other NBS J. Atmospheric and T errest. Phys . 17,255- 270 (1960) _ p ersonnel who have contributed substantially to the (Paper 66D2- 183) 166 1_ ... -