A Study on Propagation of Long Wave Signal in India

Indian Journal of Radio & Space Physics Vol. 8, October & December 1979, pp. 338-343

AWDHESH KUMAR* & MANGAL SAIN Research Department, All India Radio, New Delhi 110002

Received 30 March 1979; accepted 17 July 1979

The field strengths of If beacons and broadcasting stations, namely, Radio Tashkent and Radio Alma• Ata have been recorded at 33 places in Rajasthan during the period Aug.-Oct. 1978. The range of frequencies monitored is between 155 and 384 kHz with the path length varying between 10 and 2000 km. These data have been analyzl~d to study the diurnal variations of day- and nighttime field strengths, fading at If and atmos• pheric radio noise prevalent in Rajasthan. The results have been compared with the theoretical values esti• mated from various CCIR and RTPRC empirical formulae. Modification in the existing CCIR formula for the field stre:ngth has been suggested.

1. Introduction using a Philips field-strength meter, with charge/dis• Recently, the Research Department of All India charge time-constant as 1 msec/600 msec and a pen Radio has undertaken the detailed investigations at and ink recorder (Evershed-Vignoles type) with the If on various aspects like ground wave and sky response time of 400 msec. The recordings have been wave propagation during day- and nighttime, fading done at a speed of 12 in/hI' so as to obtain the of nighttime signal and atmospheric radio noise.1-3 shorttime variations of signals. The day- and night• The data collected during the last 20 yr at Delhi of time field strengths at each station have been recor• two long wave broadcasting stations, namely, Radio ded at least for 5 min at each receiving station as far Tashkent (164 kHz; 69°12'E; 4Io25'N) and Radio as possible. At a few selected stations the recordings Alma-Ata (182 kHz; IrE; 43°17'N) have been have also been done continuously for longer dura• analyzed for this purpose. The conclusions drawn tions to study the fading and variations of signal. The from these two circuits need to be confirmed by variations in the field strengths during sunrise and more comprehensive If data. It is in this context sunset have also been recorded for distant If stations. that the measurements have been carried out in The data thus collected have been analyzed and Rajasthan areas in India on 15 If beacon stations. the median values of field strengths have been read The day- and nighttime recordings of the field out from the recordings. The half-hourly median strengths as well as those of atmospheric radio noise values of the selected beacons recorded for longer have been made at 33 different places in Rajasthan durations have been obtained from the recordings. during Aug.-Oct. 1978. The field strengths of The variations of field strengths during sunset and Radio Tashkent and Radio Alma-Ata have also been sunrise have also been read out from the recordings recorded both during the day- and nighttime at these for different frequencies at various places. Similarly, places. The data have been analyzed to study the the noise data at 155 kHz have been analyzed by diurnal variation of field strength and atmospheric dividing the day into 6 blocks, each of 4 hr duration radio noise, sunrise and sunset effects and fading at as recommended by CCIR rep. 322-1 (Ref. 7) and If. The field strengths have also been estimated by the median value of noise in each time block has using CCIR Rec. 368-2, Rep. 265-3, Rep. 575 been obtained. For fading, the data of 4 hI' before (Annexure)4'5 and RTPRC empirical formulae6 and sunrise and 4 hI' after sunset have been chosen for compared with the observed values. The results of analysis. Hourly median values of typical samples these analyses are presented in this paper. free from interference and noise have been read out from the recordings and the fading frequency and 2. Analysis of Data depth of fading have been calculated. The data of fil~ldstrength, noise and fading have been collected in Rajasthan during Aug.-Oct.'78 3. Diurnal Variation of Field Strength ·Present address : Commercial broadcasting service, All In order to study the variations in the field India Radio. Jaipur 302 001. strengths and to compare them with the theoretical

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values, the actual ERPs of the transmitters have and (iii) the region in which the sky wave dominates been ascertained as far as possible. The beacons over the ground wave, In all the cases it is found that located in and around Rajasthan have been recorded the daytime field strength is almost steady within at distances ranging between 5 and 10 km and the ± 1'5 dB and no abnormal fading has been observed ERPs have been calculated using the CCIR ground in the region of ground and sky wave of comparable wave propagation curves corresponding to soil con• magnitude, The typical daytime field strengths for ductivity oflO-2 81m (CCIR), A value of soil conduc• each beacon station monitored at different places in tivity of-l0-2 Sim has been assessed on the basis of Rajasthan have been shown in Table 1. The theoreti• our observations of medium wave field strengthS cal values offield strength for each beacon estimated throughout Rajasthan except for northwest region by using CCIR Rec, 368-2, Rep, 265-3 and RTPRC where this value is low. It is found that the actual empirical formulae have also been included in the ERP of the transmitter ig:much lower than the speci• table for comparison, It is evident from Table I that fied value in almost all the cases except for Pune (381 the ground wave dominates over the sky wave for path kHz), Nagpur (372 kHz) and Bombay (265 kHz). lengths of the order of 700 km while the two become The variations of field strength during day- and comparable for path lengths over 800 km, The sky nighttime have been normalized to 1 kW of wave takes over the ground wave for path lengths ERP, above 1200 km, 3.1 Daytime Variations It can be seen from Table 1 that the theoretical The diurnal variations of daytime field strength values estimated from CCIR formula are in agree• for beacons and broadcasting stations at If for short ment within ± 4'0 dB with the observed ones in all and long distances have been studied for normalized the cases where the actual ERP of the transmitter ERP of 1kW, These variations have been studied in could be established, while those estimated from detail for (i) the region in which ground wave domi• RTPRC empirical formulae are widely different from nates over the sky wave, (ii) the region where ground the observed values, The variation shows irregular wave and sky wave are theoretically within ± 6 dB pattern with frequencies and path lengths, sultant48'043'046'050'065'055'056'060'0wave theoretical -14'9Jl'8Re--2'7-12'0-3'0-2'8U'O11'0-5'024'91750164037'0minus11'215'242'028'931'128'0do'32'314'58'3Con-31'930'5do·9'196726'413'27'031'610'2-0'4.RTPRCvalue19'037'566'765'057'260'050'027'645'351'163039'0'J7'537547'915'253'020546'813835022'146'970037'0102319length48534550'025'11'3do·-do9'6Slm20'8dodo·48'042'056'02'74'926'37'443'050'024'916'38'21'53'935'6do4'9'19'2H18'20'955'018'1do13'21'746'050'037'016'410-·10'1do20'6(Rep.IN265-3)3'2130'9do31'65'49'02'032'27'2031'9 0FrequencySkyTheoreticalvalue29'2-7'1do·9'1PathObservedAskHzMt.JaipurBikanerTonk335DholpurAjmerstationKishangarhBanswaraJaipurMt,TonkChittorgarhJaisalmerDidwanaCCIRJaisalmer381368384257372228223249'5 .340185 274347'5375 Receiving164182 3xvaluedo265616 persultant)Ground Abu329 Abu 10-1RTPRCminus rep, Observedas (re-value perObserved ductivity319 fromvalueTable Soil 1 - Daytime Field Strength for Standard ERP of 1 kW (Rec, 368-2)wave TashkentAhmedabadPuneMandasorIndore Udaipur station km Transmitting ChandigarhBhopalBombayDelhiJodhpurRajkotNagpurUdaipurJamnagarAgra•Actual ERPAlma-AtaJaipur not known Daytime field strength in dB (1IloVfm) . 339 INDIAN J, RADIO SPACE PHYS" VOL. 8, OCTOBER & DECEMBER 1979

1640175041'6-12'0value33'241'9332-12'3-15'8-22'2-9'1+2'0-11'962'770040039'041'045'748561'663020553'196725'99'080036'029'035'4368-239'635046'419047'054'344'726'246'S52'051'637'S37'954'1-11'654'6do45'855'655'058'6do·35'044'7-11'724'946'044'745'454'0-5'246'451'851'6-16'048'150'041'935'151'213'240'746'742'010-155'045'3-S'555'050'7-8'034'745'135'745'135'0-1'1-6'0-8'530'4-4'347'0of42'2+7'7+4'1-1'9-9'3minus+0'4PathRep,valuetantandRep,andtantRec,26'2368-253'515'4-7'151'946'7-5'255'3-0'2dogthvity8'1-7'6-9'316'055'355'058'350'757554'311'810'435'150'148'4Rec,Rec,Rec,S/mresul-575do·55'27'554'9do8'450'0-14'054'8-9'20'37'151'2anddo·of368-2368-2do·doS4'4quency42'7Fre-45'6 3 265-3Obser-RTPRCTonk228DholpurDidwanaJaisallmer25'934'225'934'215'77'433'2 UdaipurGanganagarBanswaraMt,JaipUirJaisalmerKebriJaipurxBikaoerasstation minusvedvalue347'5372182265164257340 resul-381223249'531933510-a-ofReceiving"" per Abu len-(Anne-57SRec, 375 345valueminusxure)tant Rep, ofTableDifference Rep, tant 2 -Result- Nighttime ved Resuh- Fieldved Obser- StrengthRTPRC Obser- forved Standard As duct- per ERP Obser- of 1 Con- kW km 368·2 and265-3Rep, 265·3 ~- Tashkent • Actual ERP not known Transmitting Theoretical values stati

3,2 Nighttime Field Strength all frequencies. At longer distances of the order of The median values of the nighttime field 700 km the sky wave becomes important compared strength for different beacon stations monitored at to the ground wave field strength, Comparison bet• different places in Rajasthan have been analyzed ween the observed and the theoretical values shows a and normalized for standard ERP of 1 kW and are wide difference without any particular trend of varia• shown in Table 2, The beacons which operate during tion with either frequency or path length, The mean the daytime only have not been shown in Table 2, difference in the case of field strengths calculated The theoretical values of field strength estimated from Rep, 265-3 and 575 (Annexure) lies within ± 6 from CCIR Rec, 368-2, Rep, 265-3, Rep, 575 and ± 10 dB, respectively, The corresponding value (Annexure) and RTPRC empirical formulae have for RTPRC empirical formula is more than ± 12 dB, also been included in Tabie 2 for comparison purposes, It is seen from Table 2 that, unlike the 3.3 Sunrise and Sunset Effects daytime field strength the ground wave for all the The decrease in signal strength during sunrise frequencies under consideration dominates over the has been observed on different beacons at several nighttime skywave field strength estimated from places in Rajasthan, The sunset effect on beacons Rep, 265-3 for distances up to 250 to 300 km, The could not be observed because of the interference ground wave and sky wave are of comparable ampli• from the nearby stations, The sunrise and sunset tudes when the path lengths are between 300 and effects have been observed clearly on Radio 700 km, For longer distances, the sky wave ampli• Tashkent (164 kHz) at laipur as it is found to be free tude is more than that for the ground wave. The from local interferences, The decrease in signal nighttime field strengths estimated from CCIR Rep. strength during sunrise and its increase during 575 (Annexure) shows that the ground wave and the sunset for different If transmitting stations are shown sky wave are within ± 6 dB in strength even for in Table 3, It is evident from Table 3 that the shorter distances of the order of 190 km and this sunrise effect is quite appreciable for all frequencies trend continues up to a distance of 500 km for almost and for distances greater than or equal to 350 km. 340

liP I! II ~ 1'1' 1111 '~I " II ,II 1.1 I I ,111111:,I,:, 11'1 ItIM,,~ IIII~III'I;I III' __ HIII: "'II ' KUMAR & SAIN: PROPAGATION OF LONG WAVE SIGNAL IN INDIA IN 23'013'513'010.0Variation90065010004868'0800O'SsignalSunset68016'0675-34Seffect8'Slength6'09'0DausaDholpurJaipurJaisalmerdoBarmerReceivingTableFrequencyPathJodhpurAjmcrChittorgarhkHzBikanerOanganagarDausadB372station347'516415001641640 274'0249'S26S'O26S'O4S0 do strength3 in - Sunrise and Sumet Effects ting station effectkmSunrise Agra TashkentDelhiBhopalNagpurdododo Table 4 - Frequency and Depth of Fading Bombay Transmit-

Fac;J.jpg characteristics

Transmit-ting station Re.ceiving station Frequency kHz length Path. Fading fre- Depth of km quency fading (No, of dB fades per hour) Chandigarh45216332211002'72'32'53'01640 2'752·02'51'8505486503670810'0350800248775265'0BarmerGanganagarJodhpurPilanidoChittorgarhTonkMt.AjmerJaipur Mt.228274249'5164dododo Abu Abu BhopalTashkentAgraDelhiBombaydododo

The mean value of the decrease in signal strength during sunrise is 10'5 dB for distances up to 1000 km In the case of Radio Tashkent (164 kHz) moni• tored at Ganganagar (1500 km) the decrease at sunrise is 23 dB while during the sunset observed at each of 4-hr duration have been chosen as recom• Jaipur (1640 km) the increase is 17'4 dB. These mended by CCIR Rep. 322. At least 5-min recording values corroborate our earlier findings on Radio in each case has been done and the median values Tashkent at Delhi (1630 km). have been read out. These are presented in Table 5. It may be observed that the noise is maximum 4. Fading at If' during the nighttime and minimum during the day• Typical samples of the recordings each of I-hr time, the values being 21 dB (p.V/m) and 17'5 dB duration during night have been chosen and analyzed (p.V1m), respectively, in order to investigate the fading at If. Within the distances of the order of 300 km where the daytime 6. Conclusions signal is almost steady, a slight fading has been (i) The daytime field strength is quite steady at all observed during nighttime. The frequency and depth frequencies and at short and long distances, varia• of fading for typical samples recorded at several tion being within ± 1'5 dB. places have been shown in Table 4. (ii) The nighttime field strength is steady within It may be seen from Table 4 that the number of ± 1'5 dB up to a distance of 250 to 300 km. At longer fades per hour at If varies between 2 and 4 and the distances (more than 300 km) the variations in the depth of fading between 1'8 and 3'0 dB. It shows field strength become comparatively larger, that the fading at If is slow and shallow in nature. (iii) The sunrise and sunset effects have been observ• A few of the typical recordings done for shorter ed at various frequencies in If band for distap.ces periods are alsc included in Table 4. Although it equal to or more than 300 km, The decrease in signal may not be appropriate to calculate the fading during sunrise has a mean value of 10'5 dB for frequency from short duration samples of recordings, distances up to 1000 km. For longer distances yet these have been included in Table 4 to show that (more than 1500 km) the sunrise and sunset effects the depth of fading still remains "ithin the limit of are 23 and 17'4 dB, respectively. 3 dB. (iv) The nighttime field strength shows a fa,ding pattern at all frequencies monitored between 1()4 5. Atmospheric Radio Noise and 384 kHz and for distances greater than 300 kJ;Jl. The atmospheric radio noise at 155 kHz which The fading is slow and .;h::.llow in nature with mean is found to be free from interference has been recor• fading frequency varying between 2 and 4 fades per ded at various places in Rajasthan. Six time blocks hour and depth of fading between 1'8 and 3'0 dB.

341 INDIAN J. RADIO SPACE PHYS,. VOL. 8, OCTOBER & DECEMBER 1979

Table5 - AtmosphericRadio Noiseat 155kHz duringAug,-Oct.1978

Receiving Noise level in dB (1(JoVlm) Receiving Noise level in dB (l (JoV/m) station 0000 0400 0800 1200 1600 2000 station 0000 0400 0800 1200 1600 2000 to to to to to to to to to to to to 0400 0800 1200 1600 2000 0000 0400 0800 1200 1600 2000 0000 hrs hrs hrs hrs hrs hrs hrs hrs hrs hrs hrs hrs Jaipur 24'1 Chittorgarh 22'9 12'0 Udaipur 209 21'6 19'1 Didwana 20'0 12'0 20'0 21'6 Dadu 24'1 Mt, Abu 13'6 20'0 Phagi 156 Barmer 21'0 Kekari 20'0 Jaisalmer IS'I 14'0 20'0 Bundi 18'1 Kota 20'0 20'0 Jodhpur IS'I 20'0 Deoli 20'0 16'9 20'9 Barani village 20'0 Bikaner 140 IS'I 16'9 Tonk 20'0 9'6 Pilani 12'0 18'1 Niwai 15'6 Bharatpur 20'0 Kishangarh 19'1 Dholpur 22'3 Ajmer 20'3 8'1 21'6 18'1 16'9 20'3 Gangapur 22'9 Median values 21'0 IS'I 17'5 19'1 20'0 20'0

Table 6 - Modified Reflection Coefficient

Transmitting Receiving Fre• Path Daytime reflection Daytime field strength Difference station station quenc l length coefficient (R) in dB (l(JoV/m) between kHz km Theo- Observed Observed Theo- Modified Observed Obser- retical value value retical value and ved value value theore- and (CCIR (Rep, tical modi- Rep, 265-3) values fied 265-3) of field values strength of field strength Tashkent Ganganagar 164 1500 0'05 0'08 29'6 25'6 29'7 4'0 -0'1 do Pilani do 1625 0'05 0'046 30'9 28'S 28'0 2'4 2'9 do Dholpur do 1892 0'05 0'18 36'1 27"4 38'4 S'7 -2'3

Ahna-Ata Dholpur 182 1844 0'04 0'22 38'1 22'8 37'6 15'3 0'5 do Gangapur do 1876 0'04 0'13 32'7 22'7 32'9 10'0 -0'2 do Jaisalmer do 1950 0'04 0'11 25'1 19'3 28'0 S'8 -2'9

(v) The median value of the atmospheric radio cal formula, A modification in the existing CCIR noise at 155 kHz observed at several places has the Rep, 265-3 has been suggested by taking the observed maximum value during nighttime and minimum values of reflection coefficients in place of their during daytime, the values being 21 dB (p-V1m) and theoretical values, A few typical samples for long 17'5 dB (/LV/m), respectively, distance signals greater than 1500 km from Radio (vi) The theoretical values calculated from CCIR Tashkent and Radio Alma-Ata have been taken and Rec, 368-2, Rep, 265-3, Rep, 575 (Annexure) and the modified field strengths have been obtained . . RTPRC empirical formulae are widely different from These are shown in Table 6, It is clear from Table 6 the observed values, The variations are within ± 6 that the observed values are in good agreement dB for Rep, 265-3, within ± 10 dB for Rep, 575 with the field strengths calculated from modified (Annexure) and within ± 12 dB for RTPRC empiri- values of reflection coefficients using CCIR Rep,

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265-3. However, it has to be confirmed on data for 3. Atmospheric radio noise and minimum signal requirement longer periods. in the If band in Proceedings of the ABU/AIBD seminar relating to WARC-79, Kuala Lumpur. 4. CCIR XIII plenary assembly, Geneva, 1974, Vol. V, Rec. Acknowledgement 368-2. The authors are grateful to Mr R N Ghosh for 5. CCIR XIII plenary assembly, Geneva, 1974, Vol. VI, his valuable help and suggestions. Rep. 265-3 and Rep. 575 (Annex.) 6. Broadcasting in band 5 (If), RTPRC, Doc. No. 9/24. References 7. CCIR XIII plenary assembly, Geneva, 1974, Vol. VI, 70. 1. Long distance sky wave propagation at If, AIR res. rep., 8. Ground wave propagation of medium frequencies (Effects in press. of seasonal variation of surface moisture content), CCIR 2. Fading of distant longwave signal, AIR res. rep., in press. Doc., Study Group V. 1978.

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