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A Study on Propagation of Long Wave Signal in India

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A Study on Propagation of Long Wave Signal in India Indian Journal of Radio & Space Physics Vol. 8, October & December 1979, pp. 338-343 A Study on Propagation of Long Wave Signal in India 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 338 '111'1"lllJ! 'I' r j I 1'1 I ~I KUMAR & SAIN : PROPAGATION OF LONG WAVE SIGNAL IN INDIA 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 -14'9ObservedPath31'9Jl'8Re--2'7-12'0-3'0U'O11'0-2'8-5'0175024'9164037'0minus42'011'215'228'931'1do·25'11'3do'28'032'314'58'3Con-31'9do·30'513'29'196726'431'6-7'1do·29'27'010'2-0'4.RTPRC47'937566'765'0value37'519'050'034551'150'020553'046'845'357'260'027'663039'0'J7'515'235022'113846'937'0102700616265lengthdo10'1319185485375-do9'6Slm20'8dodo·42'048'056'0do18'110-·16'426'3do35'650'043'07'42'74'916'324'98'21'519'2H18'24'9'0'93'955'013'246'01'750'037'0(Rep.20'6IN265-3)3'2130'9do31'65'42'09'032'27'2 0FrequencySkyTheoreticalvalue9'1AskHzJaipurBikanerTonk335Mt.329AbuDholpurAjmerKishangarhstationJaipurChittorgarhBanswaraJaisalmerDidwanaTonkMt,CCIRJaisalmer381368257384372 .223249'5228340274 347'5Receiving164182 3xvalue perdosultant)Ground 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 ChandigarhBhopalBombayJodhpurDelhiRajkotNagpurJamnagarUdaipurAgra•Actual ERPAlma-AtaJaipur not known Daytime field strength in dB (1IloVfm) . 339 INDIAN J, RADIO SPACE PHYS" VOL. 8, OCTOBER & DECEMBER 1979 1640175041'6-12'0value-14'050'033'233241'9-12'3-15'8-22'2-9'1-11'9+2'046'435062'770040039'041'045'720553'148561'680036'029'063096725'99'035'4368-239'6190-0'2-5'255'3-9'254'858'645'855'055'647'054'344'745'355'026'246'S51'652'0-11'654'637'S35'044'758'355'055'345'134'735'745'137'954'1do·25'934'233'215'734'27'425'9-11'724'9do45'454'0-5'246'740'746'451'651'8-16'048'150'046'044'741'9-S'535'155'050'7-8'048'450'142'035'051'213'210-1-4'3-1'1-6'0-8'530'447'0of+0'4+7'7+4'1-1'9-9'3minus42'2PathRep,Rec,Rec,valuetantRep,368-2368-2andtantandRec,368-226'215'453'5do-7'151'946'7gthvity-7'68'1-9'316'050'754'357511'810'435'1Rec,S/mresul-575do·55'27'554'9do8'40'351'27'1anddo·ofdo·doS4'4quency42'7Fre-45'6 3 265-3Obser-RTPRCTonk228DholpurDidwanaJaisallmerUdaipurGanganagarBanswaraMt,JaipUirKebriJaisalmerJaipurxBikaoerasstation minusvedvalue347'5372265182257164340 resul-381319249'522333510-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<m kHz(Annexure) Rep, (Anne-xure) JodhpurJamnagarBombayNagpurAgraBhopalPuneAhmedabadIndoreChandigarhAlma-Ata Jaipur 3,2 Nighttime Field Strength all frequencies.
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