Signal-to-Noise Ratio Effects on the Quality of GPS Observations
Contents
1. Time unit 30s Y axis C NO dB Hz SY22 Elevation angle f Time Azimuth f Time V22 CINO f Time 25 19 Zoom 40 LRI RS E T 0 50 100 150 200 250 Time from 200 to 450 Legend NovAtel August 08 09 2000 Tri M Mighty Mouse August 04 05 2000 Tri M Big Brother August 03 04 2000 _ ___ Tri M Mighty Mouse II August 02 03 2000 Comments SV22 reaches a high elevation angle as SV31 These plots point out the same trend increasing C NO values until a 50 elevation angle and then constant values and the most significant the bump at the highest elevation angle and its relationship with the steep slope of the azimuth angle evolution Remark We can observe a drop in the elevation angle and the azimuth in the data collected by Tri M Big Brother August 03 04 I checked the different files and that bump appears at the same time The antenna was tracking 12 satellites then 10 and then 11 which can perhaps explain that gap in the observations 20 e Satellite in view SV20 As SV31 and SV22 I plotted elevation azimuth and C NO against time for SV20 which is a satellite with a lower elevation angle figl X axis Time 1 unit 30s Y axis Elevation and Azimuth degrees fig2 X axis Time unit 30s Y axis C NO dB Hz V 20 Elevation angle f Time Azimuth f Time 150 ber v a m 0 100 200 300 400 502. End If If Sheet9 Cells j 5 lt gt 0 Then Sheet9 Cells j 6 Sheet9 Cells j 5 End If If Sheet10 Cells j 5 lt gt 0 Then Sheet 10 Cells Gj 6 Sheet10 CellsG 5 End If Next j Dim k As Integer For k 1 To 2 Sheet 12 Cells 1 k Sheet1 Cells 1 k 6 Sheet 12 Cells 2 k Sheet2 Cells 1 k 6 Sheet 12 Cells 3 k Sheet3 Cells 1 k 6 Sheet12 Cells 4 k Sheet4 Cells 1 k 6 Sheet12 Cells 5 k Sheet5 Cells 1 k 6 29 Sheet12 Cells 6 k Sheet6 Cells 1 k 6 Sheet12 Cells 7 k Sheet7 Cells 1 k 6 Sheet12 Cells 8 k Sheet8 Cells 1 k 6 Sheet12 Cells 9 k Sheet9 Cells 1 k 6 Sheet12 Cells 10 k Sheet10 Cells 1 k 6 Next k End Sub 30
3. blocks of satellites 3 My study Therefore the purpose of my project is to study SNR by comparing satellites evolutions elevation and azimuth angles and the different satellites 3 Observations I collected NMEA data from the GPS NovAtel RT120 receiver using 4 different antennas NovAtel 501 Tri M Mighty Mouse Tri M Big Brother and Tri M Mighty Mouse II for periods of 24 hours using an observation interval of 30 seconds I fixed the antennas one at a time on a tripod on the roof of Gillin Hall building at UNB Fredericton near the cable tube which enables connecting the antenna to the receiver in E110 GPS laboratory I saved the observations by using WINSAT software and its converter and sorted the data by using EXCEL and macros developed in Visual Basic language Remark Previously I planned to also test the Tri M Skymaster antenna Unfortunately I didn t manage to track any satellite with it It is maybe a problem of connection in so far as in comparison with the other Tri M antennas the cable is separate It would be interesting to fix that problem but I couldn t due to lack of time 1 Receiver Novatel RT20 Model GPS A035 CGS95110014 UNB 00844 The NovAtel GPSCard OEM series receiver is a multi channel parallel tracking 12 channels C A code GPS receiver operating on the L1 1575 42 MHz frequency Each dedicated channel independently tracks the code and carrier phase of a GPS satellite in view and can provi
4. 0 600 SV20 CINO f Time N Ml Wi M l ii l n iH i s aT Ta a L W E h aiita m VANA on B i 35 n em 0 100 200 300 400 500 600 21 Zoom n ITEN M VMN RTO If U JI n J A TI j TTN A Legend NovAtel August 08 09 2000 Tri M Mighty Mouse August 04 05 2000 Tri M Big Brother August 03 04 2000 __ Tri M Mighty Mouse II August 02 03 2000 Consequences As expected that low elevation angle satellite gives worse C NO values than the two high elevation angle satellites We can observe the same increasing and stable area in C NO area and the bump at the highest elevation angle Nevertheless the slop is less steep than the other satellites The usual gain pattern as describes 2 3 can account for that drop 22 5 Conclusion My study points out some of the factors which can affect C NO values such as satellite antenna gain pattern receiving antenna gain pattern antenna preamplifier gain multipath interference and receiver noise I also compared different antennas NovAtel 501 Tri M Mighty Mouse Tri M Mighty Mouse 2 and Tri M Big Brother which gave the best performance in terms of C NO values To develop this project and the knowledge of SNR effects on the quality of the GPS observations I would compare C No with elevation angle and azimuth for each satellit
5. Signal to Noise Ratio Effects on the Ouality of GPS Observations Sophie HETET Supervisor Richard B Langley August 30 2000 Department of Geodesy and Geomatics Ecole Superieure des Geometres et PO BOX 4400 Topographes Fredericton NB 1 Boulevard Pythagore Canada E3B 5A3 72000 Le Mans France N UNB Table of Contents I Introduction What is GPS How does it work GPS antenna GPS receiver performance Topic of my project work 2 Purpose of my study 1 SNR and its relationships to the uncertainty of GPS observations 2 The different effects on SNR 3 My study OV ee ae 3 Observations 1 NovAtel receiver 2 Antennas 3 NovAtel WINSAT software and NMEA interface ps 4 How to sort the data 4 Analysis SNR 0 C NO f Time Average C NO f Azimuth Average C NO f Elevation angle Study of different satellites in view A RW N 5 Conclusion 6 References 7 Appendix p p plo pll pll p13 p14 p15 p23 p24 p25 1 Introduction 1 What is Global Positioning System The Global Positioning system GPS is a space based radio positioning and navigation system that provides 24 hour all weather world wide coverage with position velocity and timing information It is composed of a space segment a control segment and a user segment The space segment is a constellation of 25 satellites divided in different blocks specifically II ITA and IIR SV11 SV13 and SV20 who
6. c of my project work My project was to study the variation of the signal to noise ratio of the GPS signals with satellite elevation angle and azimuth and from satellite to satellite for different antennas 2 Purpose of my study I SNR and its relationships to the uncertain of GPS observations The level of GPS receiving eguipment system noise determines in part how precisely pseudorange and carrier phases can be measured It is measured by the signal to noise ratio SNR where S is the power of the received signal and N the noise power at baseband which means at the band occupied by the signal after demodulation We also describe the signal level against the noise level the carrier to noise density ratio C NO which represents the SNR in a 1Hz bandwidth The effect of the noise is assessed by e The code tracking loop or delay loop DLL is given by ee mal Z where is the dimensionless DLL discriminator correlator factor BL is the equivalent code loop noise bandwidth Hz c n is the carrier to noise density C NO and is given by c n0 10 10 with C NO in dB Hz T is the inverse of the predetection bandwidth Ac is the wavelength of the PRN code 293 05m for C A code 29 305m for P code e The carrier tracking loop similarly to the code tracking loop is given by ou si where BP is the carrier loop bandwidth Hz is the wavelength of the carrier e These factors linked to the signal to noise ratio or car
7. de pseudorange accuracy within 10 cm The NovAtel product is able to measure and output satellite code and carrier phase data at a rate of up to 20 times per second and can compute up to 10 position solutions per second 2 Antennas Novatel e Active GPS Antenna Model 501 CGA95060099 Tri M e Mighty Mouse Model SM25 S N 2503276 Big Brother Model SM66 S N 6994330 Mighty Mouse II D010370 Table of specifications Sources antennas user manual 114diameter x 58 6height 58x48x15 58x48x15 58x48x15 m TNC Universal FME to TNC Universal FME to TNC Universal FME to TNC Cable Independent RG174 U Integrated RG174 U Integrated RG174 U Integrated RG223 U Loss 7dB Intercomp P N 2 2232A Operating temperature 45 C to 85 C 30C to 85 C 30C to 85 C 40C to 85 C Freguency MHz 1575 42 1575 42 1575 42 1575 42 Gain pattern dB ele 90 9 5 5 el 15 gt 0 el 10 1 1 el 5 gt 3 gt 1 gt 1 el 30 lt 10 ELE 4 5V 0 5 22mA max 5V 12mA 5V 12mA 2 5 5 5V 5mA Noise figure dB 3 0 3 6 max 1 5 2 5 max 1 5 2 5 max 1 6 Remark As the length of the cables is 5m the location on the roof is very close to the tube to enable the connection to the receiver in the lab 3 NovAtel WINSAT Software and NMEA Interface NMEA 0183 is a GPS receiver interface standard It has been developed by the National Marine Electronics Association for interfacing marine electronic devices The concept of the standard is talkers and li
8. e as I expect satellite transmitter power varies from satellite to satellite Moreover it would be interesting to identify the satellites with high multipath and remove their observations from the data to measure how strong is the multipath effect on C NO values Then it would be better to use another software to sort all the data A file of 24 hours observations contains about 200 000 data So the sorting process with EXCEL and macros developed in Visual Basic language is very slow and complex and EXCEL is not useful to plot properly such a lot of data MATLAB software would perhaps be more efficient 23 6 References A Primer on GPS Antennas by Richard B Langley GPS World INNOVATION July 1998 GPS Receiver System Noise by Richard B Langley GPS World INNOVATION June 1997 GPS Theory and Practice by B Hofmann Wellenhof H Lichtenegger and J Collins Ath edition SpringerWienNewYork 1997 NMEA 0183 A GPS Receiver Interface Standard by Richard B Langley GPS World INNOVATION July 1995 NMEA 0183 Standard For Interfacing Marine Electronics Association Version 2 30 March 1 1998 Tracking Vehicles using GPS and Packet Radio by Geoffroy de Montigny Geodetic Research Laboratory UNB August 14 1999 Memorandum GPS SNR Observations by Paul Collins and Peter Stewart Geodetic Research Laboratory UNB July 21 1999 Possible Weighting Schemes For GPS Carrier Phase Observations in the Presence of Multipath by Paul Colli
9. e column of data Sub col Dim 1 As Integer Dim j As Integer For i 1 To 7960 For j 1 To 6 Sheet1 Cells 7960 J Sheet1 Cells 1 j 6 Sheet1 Cells i 15920 J Sheet1 Cells 1 j 12 Sheet1 Cells i 23880 J Sheet1 CellsG j 18 Next j Next 1 End Sub 25 Macro elaz to create 2 sheets by elevation angle and azimuth Sub elaz Dim 1 As Integer For 1 1 To 28000 Sheet2 Cells 1 1 Sheet1 Cells 1 4 Sheet2 Cells 1 2 Sheet1 Cells 1 6 Sheet3 Cells 1 1 Sheet1 Cells 1 5 Sheet3 Cells 1 2 Sheet1 Cells 1 6 Next 1 End Sub Macro svO to delete the SNR values equal to 0 Sub svO Dim 1 As Integer M For 1 2 To 30000 If Sheet1 CellsG 6 lt gt 0 Then M Sheet2 Cells 1 1 Sheet1 Cells 1 1 M Sheet2 Cells 1 2 Sheetl Cells 1 2 M Sheet2 Cells 1 3 Sheetl1 Cells 1 3 Sheet2 Cells 1 4 Sheet1 Cellsq 4 Sheet2 Cells 1 5 Sheet1 Cellsq 5 Sheet2 Cells 1 6 Sheet1 Cells 1 6 End If Next 1 M End Sub Macro sat to sort the data by satellite Sub satl Dim 1 As Integer 26 For 1 1 To 10000 If Sheet11 Cells 1 3 1 Then Sheet1 Cells 1 1 Sheet11 Cells 1 1 Sheet1 Cells 1 2 Sheet11 Cells 1 2 Sheet1 Cells 1 3 Sheet11 Cells 1 4 Sheet1 Cells 1 4 Sheet11 Cells 1 5 Sheet1 Cells 1 5 Sheet11 Cells 1 6 End If If Sheet 1 Cells i 3 2 Then Sheet2 Cells 1 1 Sheet11 Cells 1 1 S
10. es BB _ Tri M Big Brother antenna Y axis C NO dB Hz MM Tri M Mighty Mouse antenna MMII Tri M Mighty Mouse 2 antenna Tri M Big Brother August 03 04 p f Elevation angle Azimuth 13 Comments The first plot points out two drops in the northern and southern areas The polar plot explains the bump in the North by representing the fact that there is no satellite in view in this area The second drop at an azimuth around 180 can be accounted for by the location of the antenna on Gillin Hall roof Indeed the penthouse on the roof prevents tracking satellites from this area of the sky 4 Average C NO f elevation angle e All the sets of data 50 48 46 n 0507 42 n 0607 2 mm 1907 gt bb 2407 g0 mm2 2707 mme2 0208 bb 0308 mm 0408 n 0808 36 34 32 30 SF O RD 8 O SGP MK PHS PHP WOE wD LP AD O SO E O H O BOA LE H Elevation angle Legend N NovAtel antenna X axis Elevation degrees BB _ Tri M Big Brother antenna Y axis C NO dB Hz MM Tri M Mighty Mouse antenna MMII Tri M Mighty Mouse 2 antenna I plotted Average C NO f Elevation angle for each set of data 3 sets with the NovAtel antenna and 2 sets with each Tri m antennas I calculated the average of C NO values for each elevation angle General trend This plot shows the trend of carrier to noise density against elevation angle For low elevation angle below 50
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12. h 3 GPS antenna The GPS antenna receives the energy of the electromagnetic waves arriving from the satellites and has to convert it into an electric current that can be processed by the electronics of the receiver The size and shape of the antenna are very significant characteristics as they control the antenna s ability to pick up and pass on to the receiver the very weak signal provided by the satellites The gain pattern is also an important property of a GPS antenna It describes its sensitivity over some range of elevation and azimuth angles and its ability to discriminate against some multipath signals The GPS antennas are typically omnidirectional with a nondirectional pattern in azimuth and a directional pattern in elevation angle NovAtel 501 antenna elevation gain pattern GPS Anicnoa Elevatlon Gain Patter GFS Antenna Elevalian Galn Pattern Alght Hand Circular Polarization Lett Hand Clreular Folarlzailon Generally an antenna is combined with a low noise preamplifier LNA that boosts the level of the signal before it 1s sent to the receiver 4 GPS receiver performance The performance of a receiver is assessed by its ability to precisely measure the pseudorange and carrier phase which depend on noise linked to the signals in the receiver s tracking loops The quality of the signal in the presence of noise is measured by the signal to noise ratio SNR The larger the ratio is the stronger the signal 1s 5 Topi
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14. ines e Sort by column sat and delete checksum e Create a new sheet svO run the macro svO to delete the SNR values equal to zero and sort by sat then by date then by time 2 How to sort the data by satellite e Create 3 files with a sheet by satellite file ddmm 1 xls satellites 1 to 10 file ddmm 2 xls satellites 11 to 20 file ddmm 3 xls satellites 21 to 31 and copy the data in each file in sheet11 data e Create sheet for each satellite and 1 sheet SNR e Write the calculation of average of SNR and SNR without O values by AVERAGE E E and AVERAGE F F in columns G and H of all the sheets satellite e Run macro sat 3 Others macros e I developed others macros in EXCEL to sort the data to make the different plots below e All the macros are listed in Appendix 10 4 Analysis 1 SNR 0 I plotted the averaged C NO values against elevation angle and azimuth and these plots indicate some values equal to zero I also checked my data s files and the tracking of satellites by observing WINSAT processing After having looked at the interface working it seems that the SNR value equal to O correspond to a phase in the observations when the receiver is tracking a satellite but can t lock that observation Most of the time it appears o the first time the satellite is visible o when the elevation angle is about 5 degrees until 10 degrees o when the azimuth is between 170 a
15. lock I antenna The Block ITA satellites are essentially identical to the standard block II with one exception In the event the ground stations are unable to upload new navigation information the satellites will continue to transmit the same navigation message for up to 180 days From a user standpoint signals from the Block IIA the orbit of the satellite will change over this period of time Without periodic navigation updates from the ground the accuracy of the system will degrade over time However the system would at least still be operational The Block IIR satellites feature autonomous navigation That is they can create their own navigation messages without uploads from the ground This allows the system to maintain system accuracy for much longer periods between contacts with the ground Then the Block IR satellites are any different compared to the constellation of Block II IIA satellites and perform at the same power levels 16 5 Study of different satellites in view e Satellite in view SV31 These plots describe the elevation angle and azimuth against time and C NO against time of the satellite in view SV31 for four 24 hours observations figl X axis Time 1 unit 30s Y axis Elevation and Azimuth degrees fig2 X axis Time unit 30s Y axis C NO dB Hz SV31 Elevation f Time Azimuth f Time 210 SY31 CINO f Time 50 V P nd il 45 i _ iia i tf she ia HP Af Pi l T m i
16. nd 210 degrees indeed that range 1s unusable due to signal blockage Then I decided to study the data after having deleted the SNR value egual to 0 2 C NO f Time These plots represent the raw values of 24h of observations against time for all the four sets of data Tri M Mighty Mouse II August 02 03 Tri M Big Brother August 03 04 Tri M Mighty Mouse August 02 03 and Novatel August 08 09 I plotted time in x axis which unit is hhmmss where h is hour m minute and s second and C NO in y axis which unit is dB Hz Results These plots show the range of the C NO values for these four days of observations O NO A DT s CVO E A ttt I ON O gt O NO M O0 WO St 4 st VV VV O ce oo LAZZ OUUD VV VV ON o mn lt A o ee m 5 5 o bo gt 52 PEPR lt 2D op ee or Zanes S222 Ze RE Then the antenna providing the strongest signal seems to be the Tri M Big Brother as we could expect given the higher gain of its preamplifier 12 3 Average C NO f Azimuth I plotted the averaged SNR values against azimuth for the nine sets of observations I did And the polar plot shows the elevation and azimuth of all the satellites in one day of observations Average CINO f Azimuth p DLA W A UW ay I Min A Eu AN il O hy WA PRO WN A el a EN R ISET OE BOB SONS shin Legend N NovAtel antenna X axis Azimuth degre
17. ng distance between satellites and receiver e Receiving system s impacts Antenna s effects The amount of noise power from a particular source intercepted by an antenna depends on the directions from which the electromagnetic waves arrive and the gain of the antenna in that direction The sensitivity of an antenna is linked to its size shape and location So these characteristics have impact on noise power and also signal power Receiver s noise The receiver noise consists of cable losses and noise generated internally in the receiver The signal travelling through a coaxial cable between the antenna and the receiver or the preamplifier is attenuated That attenuation depends on the type and the length of the cable Moreover improper matching antenna and receiver connectors can generate more loss and delay Furthermore as the power to extract a GPS signal is concentrated in the receiver noise is partly produced by the receiver And most of the time a low noise preamplifier LNA is combined to the receiver or the antenna active antennas to increase the signal s level Its performance is given by its noise figure typically about 1 2 to 2 5 dB e Satellites effects The variation of C NO values depends on the satellite transmitter s power output and differences in satellite and receiver antenna gain with elevation and azimuth angles It is also due to losses engendered by the other satellites in view and the various
18. ns and Richard B Langley Geodetic Research Laboratory UNB March 1999 WINSAT Graphical Interface Program User Manual NovAtel Communication Ltd GPSCard Command Descriptions Manual NovAtel communication Ltd GPSCard OEM Series Installation and Operating Manual NovAtel communication Ltd Introduction to GPS Applications by John T Beadles http www redsword com gps A Comparison of four popular AMPLIFIED GPS ANTENNAS by Joe Mehaffey http joe mehaffey com gpsantrev1 htm Test Results of some Low Cost GPS Antennas by David Martindale http www gpscables com ant test htm http home 2 worldonline nl samsvl anttest htm http home 2 worldonline nl samsvl anttable htm http home 2 worldonline nl samsvl mm2test htm 24 7 Appendix macro developed in Visual Basic 1 Macro time to insert time and day of observations Sub time Dim i As Integer Dim j As Integer M For 1 1 To 11000 M Forj 1To3 If Sheet1 Cells i 1 GPZDA Then If Sheet1 CellsGi j 1 GPGSV Then Sheetl Cells 1 J 5 Sheet1 Cellsq 2 Sheet1 Cells 1 j 11 Sheetl Cells 1 2 Sheet1 Cells i j 17 Sheet1 Cells 1 2 Sheet1 Cells 1 j 23 Sheet1 Cellsq 2 Sheet1 Cells i J 6 Sheet1 Cellsq 3 Sheet1 Cells i j 12 Sheet1 Cellsq 3 Sheet1 Cells 1 J 18 Sheet1 Cells 1 3 Sheet1 Cells 1 J 24 Sheet1 Cellsq 3 End If End If Next j Next 1 End Sub 2 Macro col to sort the data and obtain on
19. rier to noise density have effects on the weigh matrix P in the least squares method of data analysis and then on the uncertainty of the observations 2 The different effects on SNR In radio based communication and navigation systems noise comes from various sources the equipment and natural terrestrial and extraterrestrial sources e Natural effects A GPS receiver s antenna picks up a certain amount of noise in the form of naturally produced electromagnetic radiation This radiation comes in part from the sky The sky noise is composed of the effect of the random electromagnetic radiation emitted by the sun the Milky Way and other discrete cosmic objects It depends too on the earth s atmospheric conditions absorption and re radiation of the GPS signals The electromagnetic radiation is also due to the ground and objects in the environment of the receiver The phenomenon of multipath explains losses and gains in the strength of the satellites signals It is caused by reflecting surfaces near the receiver Moreover the antenna s location can bring about a reduction in signal intensity particularly if signals pass through structures like wooden frame houses automobile dashboard or window recesses of aircraft It is worth pointing out others environmental factors such as temperature moisture salt vibration and mechanical shock which can effect the performance of a GPS antenna These space losses change also with a varyi
20. se identification is composed of numbers Pseudo Random Noise PRN code and orbital position number The control segment consists of a system of tracking stations located around the world and a master control station Then the user segment is composed of equipment that receives and tracks the satellite signals such as the NovAtel receiver used in my work 2 How does it work The satellites in view broadcast 2 microwave signals at the L1 frequency 1575 42 MHz and L2 frequency 1227 60 MHz LI provides the Standard Positioning Service The L2 is used to measure the ionospheric delay by Precise Positioning Service equipped receiver US Military L1 and L2 carrier phases are modulated by 3 binary codes The C A Coarse Acquisition Code and the Navigation Message modulate the L1 carrier phase The former code gives the civil SPS whose accuracy used limited through the application of a process called Selective Availability and is no longer in effect now The later describes the GPS satellite orbits clock corrections and other system parameters The P Precise Code modulates both L1 and L2 carrier phases and gives the PPS It is encrypted to prevent use by unauthorised users The encryption process is known as Anti Spoofing There are different sources of errors in GPS noise and bias Noise errors include receiver noises Bias errors result from satellite clock errors ephemeris data errors tropospheric and ionospheric delays and multipat
21. steners For GPS observations the talker is the GPS receiver and the listener is a computer that receives the data The transmissions of the data use plain text with characters coded using 7 bit ASCII and are made in serial which means bits are sent one at a time with one bit following the next Moreover the data are transmitted at a rate of 4 800 bits per second Then data are sent from a talker to a listener in the form of sentences with a maximum length of 82 characters NovAtel WINSAT is a software that records displays and interprets the data sentences My study requests information about time elevation angle azimuth and signal to noise ratio So I chose to log in GPGSV and GPZDA sentences in WINSAT software The GSV sentence provides the number of satellites in view and for each satellite its PRN number elevation angle azimuth and carrier to noise density And the ZDA sentence gives time and date of observation GSV Satellites in view GPGS V Total Message Total Satellite Elevation Azimuth SNR Oo check number of number number of ID angle 0 to 360 C NO A SV sum message 1 to9 satellites in number 0 to 90 deg 0 to 99 to 3 view deg dB Hz ZDA Time and date Settings Menu I have used a NovAtel OEM card The configuration I used is PC Port COM2 OEM Port COMI Window Menu First I have specified different functions in Command Control gt unfix to unfix the position gt ecutoff 0 to collect all the da
22. t 04 05 2000 50 50 48 48 E n estes 46 577 Dx ate an i AK y if PR VY 42 SD P SOE sg aii n jh 40 A 38 j iA fd V V A j Fi V Pi id 36 5 G ji i V h NW H h j 34 I i 34 Hy a J f A A l 32 H J M ESN 30 G g a g OSOR E E R D 2 D D E S g R Ri S A R T R EE A T RE TRETA A AT E E C iR iR iR iR A E g A A TE g aa a R E a R p p E G E E T a a a n E R DR E E E I e N T A a R Ri eS E 30 FHT o L5 o OF OF o N GL t ico BS aR am A8 o pth ODO S SE ENAAN An 8 AS S S D58 O 8 RR RDG 6065 Elevat gle Elevation angle 15 Tri M Big Brother August 03 04 2000 Tri M Mighty Mouse II August 02 03 2000 Conseguences It seems that there is no particular difference between the two blocks of satellites It also depends on the antennas I used The C NO values vary by 1 or 2 units SV11 gives the most variable plot SV13 and SV20 give better SNR values than the Block II A But I can t clearly define any general trend Indeed the Block II satellite is designed to provide reliable service over a 7 5 year life span The satellite design reguires minimal interaction with the ground and allows all but a few maintenance activities to be performed without interruption to the signal broadcast Periodic uploads of data from the control segment cause no disruption to service The improved Block II antenna provides slightly greater gain than the B
23. ta for an elevation angle from 0 to 90 deg Then I have made the configuration of the observations in Logging Control gt Edit logs NMEA then GPGSV and GPZDA gt Trigger On time period 30 0 s gt Output Save as a GPS file ASCII and binary mixed gt Time 24h of collecting gt Start log To check the good evolution of the testing it is possible to observe the tracking of satellites in view by using Command Tracking Status the good solution of the position of the antenna by reading Position and to note the recording by loading ASCII Records Converter When the logging is finished it 1s advised to use the converter linked to WINSAT to avoid the junk data and convert the selected file to ASCII Format logs as the NMEA format logs are not clearly defined as ASCII or binary format 4 How to sort the data 1 How to sort by elevation angle and by azimuth e Open the file gps with EXCEL by using separations by comma and and save it ddmm sv xls e Insert a line of legend sat elev az snr sat elev az snr sat elev az snr sat elev az snr e Insert 2 columns before the columns called sat e Run the macro time to insert time and day of observation and sort by columnA e Cut GPZDA lines and create a new file ddmm t xls to paste these data e Make one column with GPGSV lines and delete the 4 first columns by running macro col after having checked the number of l
24. the carrier to noise density increases It reaches its highest value at 50 and becomes stable 14 C NO Drops All the curves are scattered I guess that multipath effects can explain the bumps at the same elevation angles for each set of data It is worth remarking that those drops are more significant at elevation angles below 50 Comparison of the antennas The Big Brother s signal to noise ratio values are largely 2 or 3 units larger than the other antennas during the two days of observations The Tri M Mighty Mouse antenna gave better results August 02 and 03 than July 19 and 20 I wonder what can account for that irregularity I checked my observations file and I pinpointed that I have less information the first day of data than the second one In general its results are better than Tri M Mighty Mouse II and Novatel antennas The Tri M Mighty Mouse II and Novatel antennas are very close in performance e Comparison between the block II IIA satellites and block IIR satellites I plotted the averaged values of C No dB Hz against elevation angle degrees for the entire IT IIA block of the satellites and for each IIR satellites SV11 SV13 and SV20 for 4 sets of observations Tri M Mighty Mouse 2 August 02 03 Tri M Big Brother August 03 04 Tri M Mighty Mouse August 04 05 and NovAtel 501 August 08 09 Novatel August 08 09 2000 Tri M Mighty Mouse Augus
25. tk s M V h br ji dd ni We if p aa 35 A 30 25 17 Zoom N 08 08 MM 04 08 7 BB 03 08 MMII 02 08 Time from 200 to 500 Legend NovAtel August 08 09 2000 Tri M Mighty Mouse August 04 05 2000 Tri M Big Brother August 03 04 2000 Tri M Mighty Mouse II August 02 03 2000 Results The plots show how the signal strength varies for a satellite with a high elevation angle The expected consequences are obvious the SNR value increase as the elevation is higher and becomes constant as the satellite reaches a 50 elevation angle But the second plot C NO f Time describes a drop when the elevation angle is the highest 50 The third plot a zoom at an elevation angle of 50 confirms that drop Concerning the azimuth the angle value shift very quickly it drops down from 180 to 60 in little time It maybe can explain the bumpiness of C NO values Remark There is a drop down of the elevation angle in the observations with Tri M Big Brother August 03 04 I checked the EXCEL file and the ASCII file I found the same drop 18 e Satellite in view SV22 As previously I plotted elevation angle and azimuth against time and C NO against time for the satellite SV22 figl X axis Time 1 unit 30s Y axis Elevation and Azimuth degrees fig2 X axis
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