satellite communication (217100 7)€¦ · the received antenna gain to system noise temperature...

SATELLITE COMMUNICATION

(2171007)

B.E. 7TH SEM LABORATORY MANUAL 2016

DEPARTMENT OF ELECTRONICS AND COMMUNICATION

GOVERNMENT ENGINEERING COLLEGE-MODASA

CERTIFICATE

This is to certify that Mr. /Ms. _____________________________________________

Enrollment no._______________________ of Seventh semester of B.E____________________

Class has satisfactorily completed his/her one full semester in “2171007 SATELLITE

COMMUNICATION” satisfactorily in partial fulfillment of Bachelor of Electronics and

communication Engineering degree to be awarded by Gujarat Technological University.

Prof. K.V.Patel

Prof. K.R.Patel

Date: - …. /… /…….

INDEX

EXP.

NO.

EXPERIMENT NAME PAGE

NO.

DATE OF

EXPERIMENT

SIGNATURE

1 Establishing a direct communication link between Uplink Transmitter and Downlink Receiver using tone signal

2 To implement matlab code to determine look angle (azimuth and elevation) of satellite

3 To implement matlab code for uplink and downlink budget calculation.

4 Transmitting and receiving three separate signals (Audio, Video, Tone) simultaneously through satellite link.

5 Transmitting and receiving Function generator waveforms through satellite link.

6 Transmitting and receiving PC data through satellite link.

7 Study the delay between Uplink Transmitter and Downlink Receiver during data transmission.

8 To calculate the carrier to noise ratio of established satellite link

9 To calculate signal to noise ratio of established satellite link.

10 To study the global positioning system and GPS receiver.

SATELLITE COMMUNICATION LAB MANUAL GEC MODASA Page 1

Experiment: 1

Objective:

Establishing a direct communication link between Uplink Transmitter and Downlink Receiver using tone signal

Equipments Needed:

• Uplink Transmitter

• Dish Antennas

• Downlink Receiver

• Connecting cables

Introduction: Uplink Transmitter controls

Procedure:

Setting at Uplink Transmitter:

Connect the Uplink Transrnitterto AC Mains.

Attach Antenna to Uplink Transmitter with BNC -BNC lead.


Switch 'ON' the Uplink Transmitter and frequency display will come on. The transmitting frequency can be selected by 'Frequency Select' key. The available frequencies are 2414/ 2432/ 2450/ 2468 MHz.

Select uplink frequency to 2468 MHz.


Note: It is suggested to select the higher frequencies 2468/ 2450 MHz always for Uplink transmission.

Now set the "Channel B" to 'Tone' mode using the 'Channel Select B' key, so as to transmit tone signal from Uplink Transmitter. The 'Tone' signal is transmitted through 'Audio II' channel of the transmitter.


The tone signal can be observed on oscilloscope at 'Tone Generator' section of Uplink Transmitter.

Setting at Downlink Receiver:

Place Downlink Receiver at a convenient distance of 5 - 7m. (It can go even up to 10m.).

Connect the Downlink Receiver to the AC Mains.

Attach Antenna to the Downlink Receiver with BNC - BNC lead.


Switch 'ON' the Downlink Receiver and frequency display will come on. The receiving

frequency can be selected by 'Frequency Select' key. The available frequencies are 2414/ 2432/ 2450/ 2468 MHz.

Select the Downlink Receiver frequency same as to Uplink Transmitting frequency ue. 2468 MHz.


Now set the 'Channel B' to 'Tone' mode using 'Channel Select B key, on as to receive

tone sq.! from Uplink Transmitter.

The tone signal can be observed on oscilloscope at 'Received Tone' section of Downlink

Receiver. Observe the variations In the frequency and the amplitude of the received tone signal by varying the frequency and amplitude of tone signal at 'Tone Generator' section of Uplink Transmitter.


Now set the 'Channel B' to 'Speaker' mode using 'Channel Select B key, so as to hear the

tone signal. The Tone signal is switched to Speaker of Receiver.

Result: A clear tone indicates that the direct communication link has been successfully setup between Uplink Transmitter and Downlink Receiver.


Experiment no: 2

Objective: To implement matlab code to determine look angle (azimuth and elevation) of satellite.

THEORY:


MATLAB CODE FOR LOOK ANGLE CALCULATION:

%Look angle calculation using Maltlab fprintf('\n\n'); fprintf('..........Look Angle parameters........\n\n'); Ls=input('satellite latitude ='); ls=input('satellite longitude ='); Le=input('Earth station latitude ='); le=input('Earth station longitude ='); rs=input('The distance between earth centre to satellite in meter ='); fprintf('\n'); Re=6378*10^3; %radius of earth in meter gama=acosd(cosd(Ls)*cosd(Le)*cosd(ls-le)+sind(Ls)*sind(Le)); d1=(Re^2+rs^2-2*Re*rs*cosd(gama)); d=sqrt(d1); %slant distance El=acosd((rs*sind(gama))/d); a=abs(le-ls); alfa=asind(sind(a)*cosd(Ls)/sind(gama)); fprintf('..........Look Angle calculation........\n\n'); if(Le>0 && ls>0) Az=180-alfa; fprintf('The azimuth angle in degree is= %f \n',Az); elseif(Le>0 && ls<0); Az=180+alfa; fprintf('The azimuth angle in degree is= %f \n',Az); elseif(Le<0 && ls>0) Az=alfa; fprintf('The azimuth angle in degree is= %f =\n',Az); else Az=360-alfa; fprintf('The azimuth angle in degree is= %f \n',Az); end fprintf('Elevation angle is = %f \n',El);


Experiment no: 3

AIM: to implement matlab code for uplink and downlink budget calculation.

THEORY:


MATLAB CODE FOR UPLINK AND DOWNLINK BUDGET CALCULATION:

fprintf('.........The uplink parameters.........\n\n');

C=3*10^8;

PI=3.14;

K=1.23*10^-23;

d=42164000;

Kdb=mag2db(K);

Ptu=input('Enter the transmit power in watt ='); %transmit power

Ptudb=pow2db(Ptu);

Wvtudb=input('Enter the waveguides loss in db =');%waveguides losses

Gtudb=input('Enter the transmit antenna gain in db =');

EIRPudb=Ptudb+Gtudb-Wvtudb;

Fu=input('Enter the uplink frequency in GHz =');%uplink frequencies

Fu=Fu*10^9;

lamdau=C/Fu;%wavelength

FSLu=((4*PI*d)/lamdau)^2;%free space calculation

FSLudb=mag2db(FSLu);

Ludb=input('Enter the other losses present in the free space in db =');%loss %present in space except the free spaceloss

Lutdb=FSLudb+Ludb;%total loss in atmosphere

Gru=input('Enter the receiver antenna gain =');%for this time the receiver %antenna gain is

% satellite antenna gain

Grudb=mag2db(Gru);

Wvrudb=input('Enter the received waveguide loss in db =');%received %waveguides loss in db


Prudb=EIRPudb+Grudb-Lutdb-Wvrudb;%received power or simply is known as %carrier power

Tsysu=input('Enter the system noise temperature in Kelvin =');

Tsysudb=mag2db(Tsysu);

GTRudb=Grudb-Wvrudb-Tsysudb;%gain to temperature ratio for satellite antenna

Nubw=input('Enter the noise bandwidth in Hz =');

Nubwdb=mag2db(Nubw);

Noudb=Kdb+Tsysu+Nubwdb;

CNRudb=Prudb-Noudb;%C/N ratio in db

fprintf('\n');

% link budget analysis for downlink

fprintf('.........The downlink parameters.........\n\n');

Ptd=input('Enter the transmit power in watt ='); %transmit power

Ptddb=pow2db(Ptd);

Wvtddb=input('Enter the waveguides loss in db =');%waveguides losses

Gtddb=input('Enter the transmit antenna gain in db =');

EIRPddb=Ptddb+Gtddb-Wvtddb;

Fd=input('enter the downlink frequency in GHz =');%uplink frequencies

Fd=Fd*10^9;

lamdad=C/Fd;%wavelength

FSLd=((4*PI*d)/lamdad)^2;%free space loss calculation

FSLddb=mag2db(FSLd);

Lddb=input('Enter the other losses present in the free space in db =');%loss %present in space

% except the free spaceloss

Ldtdb=FSLddb+Lddb;%total loss in atmosphere


Grd=input('Enter the received antenna gain =');% the receiver antenna gain

Grddb=mag2db(Grd);

Wvrddb=input('Enter the received waveguide loss in db =');%received %waveguides loss in db

Prddb=EIRPddb+Grddb-Ldtdb-Wvrddb;%received power also known as %carrier power

Tsysd=input('Enter the system noise temperature in kelvin =');

Tsysddb=mag2db(Tsysd);

GTRddb=Grddb-Wvrddb-Tsysddb;%gain to temperature ratio

Ndbw=input('Enter the noise bandwidth in Hz =');

Ndbwdb=mag2db(Ndbw);

Noddb=Kdb+Tsysd+Ndbwdb;

CNRddb=Prddb-Noddb;%C/N ratio in db

CNRt=((db2mag(CNRudb))^-1)+(db2mag(CNRddb)^-1);%total C/T ratio in db for %Uplink and

% downlink

CNRtdb=mag2db(CNRt);

fprintf('\n\n');

fprintf('........the Uplink calculation........\n\n');

fprintf('Transmit power in db is = %f\n',Ptudb);

fprintf('Wave guide loss for uplink in db is = %f\n',Wvtudb);

fprintf('EIRP in db is = %f\n',EIRPudb);

fprintf('Free space loss is in db = %f\n',FSLudb);

fprintf('The receiver antenna gain in db is = %f\n',Grudb);

fprintf('The received power in db is = %f\n',Prudb);

fprintf('Wave guide loss for uplink in db is = %f\n',Wvrudb);

fprintf('The system noise temperature in db is = %f\n',Tsysudb);


fprintf('The received antenna gain to system noise temperature ratio in db is = %f\n',GTRudb);

fprintf('The noise power bandwidth in db is = %f\n',Nubwdb);

fprintf('The noise power in the given bandwidth in db is = %f\n',Noudb);

fprintf('The Carrier to noise power ratio in db is = %f',CNRudb);

fprintf('\n\n');

fprintf('........the downlink calculation........\n\n');

fprintf('Transmit power in db is = %f\n',Ptddb);

fprintf('Wave guide loss for uplink in db is = %f\n',Wvtddb);

fprintf('EIRP in db is = %f\n',EIRPddb);

fprintf('Free space loss is in db = %f\n',FSLddb);

fprintf('The receiver antenna gain in db is = %f\n',Grddb);

fprintf('The received power in db is = %f\n',Prddb);

fprintf('Wave guide loss for uplink in db is = %f\n',Wvrddb);

fprintf('The system noise temperature is db is = %f\n',Tsysddb);

fprintf('The received antenna gain to systme noise temperature ratio in db is = %f\n',GTRddb);

fprintf('The noise power bandwidth in db is = %f\n',Ndbwdb);

fprintf('The noise power in the given bandwidth in db is = %f\n',Noddb);

fprintf('The Carrier to noise power ratio in db is = %f\n',CNRddb);

fprintf('\n\n');

fprintf('.......for uplink and downlink.......\n\n');

fprintf('The combined carrier to noise power ratio in db is=%f',CNRtdb);

fprintf('\n\n');

OUTPUT


.........The uplink parameters......... Enter the transmit power in watt =85 Enter the waveguides loss in db =2 Enter the transmit antenna gain in db =51 Enter the uplink frequency in GHz =6.1 Enter the other losses present in the free space in db =1 Enter the receiver antenna gain =23 Enter the received waveguide loss in db =0.5 Enter the system noise temperature in Kelvin =450 Enter the noise bandwidth in MHz =2.5 .........The downlink parameters......... Enter the transmit power in watt =10 Enter the waveguides loss in db =1.2 Enter the transmit antenna gain in db =30 enter the downlink frequency in GHz =3.6 Enter the other losses present in the free space in db =2 Enter the received antenna gain =41 Enter the received waveguide loss in db =1 Enter the system noise temperature in kelvin =140 Enter the noise bandwidth in MHz =2.5 ........the Uplink calculation........ Transmit power in db is = 19.294189 Wave guide loss for uplink in db is = 2.000000 EIRP in db is = 68.294189 Free space loss is in db = 401.285601 The receiver antenna gain in db is = 27.234557 The received power in db is = -307.256855 Wave guide loss for uplink in db is = 0.500000 The system noise temperature in db is = 53.064250 The received antenna gain to system noise temperature ratio in db is = -26.329694 The noise power bandwidth in db is = 127.958800 The noise power in the given bandwidth in db is = 119.756902 The Carrier to noise power ratio in db is = -427.013757 ........the downlink calculation........ Transmit power in db is = 10.000000 Wave guide loss for uplink in db is = 1.200000 EIRP in db is = 38.800000


Free space loss is in db = 392.124508 The receiver antenna gain in db is = 32.255677 The received power in db is = -324.068830 Wave guide loss for uplink in db is = 1.000000 The system noise temperature is db is = 42.922561 The received antenna gain to systme noise temperature ratio in db is = -11.666884 The noise power bandwidth in db is = 127.958800 The noise power in the given bandwidth in db is = -190.243098 The Carrier to noise power ratio in db is = -133.825733 .......for uplink and downlink....... The combined carrier to noise power ratio in db is=427.013757 Conclusion


Experiment: 4

Objective:

Transmitting and receiving three separate signals (Audio, Video, Tone) simultaneously through satellite link

Equipments Needed:

Uplink Transmitter Dish Antennas Downlink Receiver Connecting cables Satellite Transponder

Procedure:

Once you get the set up ready as per the experiment 2, proceed as follows. • Carry out the following settings at all three units starting from Uplink Transmitter then

Satellite Transponder and at last Downlink Receiver. This sequence of operation must be followed to avoid any kind of improper operation of the system.


Now set the "Channel A" to 'Video' mode using the `Channel Select A' key, so as to transmit video signals from Uplink Transmitter. The video signals are transmitted through `Video' channel of the transmitter. Similarly set the "Channel B" to 'Tone' mode using the `Channel Select B' key, so as to transmit tone signal from Uplink Transmitter. The 'Tone' signal is transmitted through `Audio II' channel of the transmitter.


Connect the audio/video signal at the input socket provided on uplink transmitter, video at video input and audio at audio-I input.

Setting at Satellite Transponder:


Keep the toggle switch to 'Telemetry off' position provided at Satellite Transponder unit.


Now set the "Channel A" to 'Video' mode using the 'Channel Select A' key, so as to receive video signals from Uplink Transmitter. The video signals are received through 'Video' channel of the receiver. Similarly Now set the 'Channel B' to 'Speaker' mode using 'Channel Select B key, so as to hear the tone signal. The Tone signal is switched to Speaker of Receiver.

Connect TV monitor to the Audio/Video output of Downlink Receiver. (Video from Video Output, audio from Audio I output) Set TV in AV Mode.


The TV monitor will display video and audio signal that you have connected to Uplink Transmitter input.

Also the tone signal can be heard in the speaker of receiver. • Try link fail by using Transponder “OFF”.

Result:

Three separate signals (Audio, Video and Tone) are successfully received at Downlink Receiver through satellite communication link.


Experiment: 5

Objective:

Transmitting and receiving Function generator waveforms through satellite link

Equipments Needed:

Uplink Transmitter Dish Antennas Downlink Receiver Connecting cables Satellite Transponder Function generator

Procedure:

Once you get the set up ready as per the experiment 2, proceed as follows. Connect Function generator Sine wave output to Audio-I socket provided on Uplink

Transmitter.


Feed the signal of 1 KHz Sine wave. Connect Audio-I socket of Downlink Receiver to the Oscilloscope.

You will observe similar wave of same frequency on Oscilloscope. • Function can be change to Triangular wave and Square wave up to 5 KHz frequency and

observe the output.

Result:

Function generator waveforms are successfully received at Downlink Receiver through satellite communication link.


Experiment: 6

Objective:

Transmitting and receiving PC data through satellite link

Equipments Needed:

Uplink Transmitter Dish Antennas Downlink Receiver Software Satellite Transponder USB cables -2 Nos Preferably 2 sets of PC's

Procedure:

Install the Satellite Communication software on both the PCs which are being used for transmitting and receiving the PC data. •

Install the USB driver if needed so that USB device is detected/ supported by the PCs. Once you get the set up ready as per the experiment 2, proceed as follows. • Carry out the following settings at all three units starting from Uplink Transmitter then

Satellite Transponder and at last Downlink Receiver. This sequence of operation must be followed to avoid any kind of Improper operation of the system.


Now set the 'Channel A' to 'PC Data' mode using 'Channel Select A' key, so as to transmit PC data signal from Uplink Transmitter. The PC Data signals are transmitted trough 'Video' channel of the transmitter.


Connect the USB cable to lisp connector of Uplink Transmitter and the other end to the USB port of PC 1.


Keep the toggle switch to 'Telemetry off' position provided at Satellite Transponder unit.


Note: To ensure the proper frequency selection, it is suggested to operate the 'Frequency Select' key to go through rather than depending on by default selected frequency. Setting at Uplink Transmitter:

Now set the 'Channel A' to 'PC Data' mode using 'Channel Select A' key, so as to receive PC data signal from Uplink Transmitter.

Connect the USB cable to USB connector of Downlink Receiver and the other end to the

USB port of PC 2.


Now check the Device manager property of PC1 and heck the Port setting to confirm the USB port number/name obtained by the Uplink Transmitter at PC1.


Open the Satellite Communication software window at PC 1 and select the same Port name/ number in the 'Transmitter' window.

Click the ‘connect’ button to connect it with the device.


In the same way check the Device manager property of PC2 and check the Port setting to confirm the USB port number/name obtained by the Downlink Receiver at PC2.


• Open the Satellite Communication software window at PC 2 and select the same Port name/ number in the 'Receiver window.


Click the ‘connect’ button to connect it with the device.

At PC1 Transmitter. Window, enter the text in text bar.


Click the 'Transmit button to transmit it. Check that the text appears in the transmitting

window.


When the link is established, the text transmitted from PC1 will be received PC2 via Satellite link. Check that the received text is appears in the Receiver window of PC2.

After completing the PC data communication ensure to disconnect the port by clicking

the 'Disconnect' buttons at both the PCs software windows to release the port so that communication can be repeated without any problem related to system support.


Note: once you finish the communication and switch off all the three units and wish to repeat the experiment, always follow the Instruction given below. In the start of any experiment; Switch 'ON' the Uplink Transmitter first and carryout all the setting required to do t e

experiment like Frequency selection, Channel A mode setting or Channel B mode setting.

After that switch on the Satellite Transponder (if applicable) and carryout the frequency setting for both; Uplink Receiver and then Downlink Transmitter.

At last switch on the Downlink Receiver and carryout all the setting required to do the experiment like Frequency selection, Channel A mode setting or Channel B mode setting.

To ensure the proper frequency selection, it is suggested to operate the 'Frequency Select' key to go through rather than depending on by default selected frequency.

while performing the experiment of PC data Communication, It is recommended to check the USB port name/ number in the properties of Device manager and also verify that the device is recognized by the PC or not In case if it need USB driver, then install it so that the device should be supported by the PC.

After finishing the PC data communication experiment, ensure to disconnect the USB port from the software window by clicking the 'Disconnect' button so that the USB ports


in used should be released properly and can be used again to perform the experiment without any problem related to system support.

Result: PC data transmitted from first PC is received in the second PC via Satellite link.


Experiment: 7

Objective:

Study the delay between Uplink Transmitter and Downlink Receiver during data transmission.

Equipments Needed:

Uplink Transmitter Dish Antennas Downlink Receiver Connecting cables. Digital Storage Oscilloscope Satellite Transponder

Procedure:

Once you get the set up ready as per the experiment 2, proceed as follows. Carry out the following settings at all three units starting from Uplink Transmitter then

Satellite Transponder and at last Downlink Receiver. This sequence of operation must be followed to avoid any kind of Improper operation of the system.


Now set the "Channel A" to 'Data' mode using the 'Channel Select A' key, so as to transmit data signals from Uplink Transmitter. The data signals are transmitted through 'Video' channel of the transmitter.


Connect the DSO CHI to Data Generator test point.


Keep the toggle switch to 'Telemetry On' position prey,. at Satellite Transponder unit.



Now set the "Channel A" to 'Data' mode using the 'Channel Select A' key, so as to receive data signals from Uplink Transmitter. The data signals are received through 'Video' channel of the receiver.

Connect the DSO CHIT to 'Received Data" section and observe the data.


The recommended DSO settings are as follows:

o Adjust the Time/Div knob at 50ms. o Adjust Volt/Div. Knob at 2V. o Set appropriate trigger level, so that the signal becomes stable on screen. o Select Acquisition mode to 'Normal' position. o Select Display 'Persist' to 'Off' position.

Now gradually rotate the 'Delay Adjust' knob and observe the changes in the delay

between the transmitted and received data.


Result: The experiment can be useful to observe simulated delay in satellite.


Experiment: 8

Objective: To calculate the carrier to noise ratio of established satellite link Equipments needed:

Uplink Transmitter Dish Antennas Satellite Transponder Downlink Receiver Oscilloscope Connecting cables

Procedure:

Connect the Satellite Uplink Transmitter to AC Mains. Switch 'ON' the transmitter by Mains switch and frequency display will light up. The transmitting frequency can be selected by Frequency Select switch. The frequency

can be changed from 2450-2468 MHz. Connect Antenna to Uplink Transmitter with BNC -BNC lead. Place Downlink Receiver at a convenient distance of 5-7m. (It can go even up to 10m.). Place a Satellite Transponder between Transmitter and Receiver at a convenient

distance; preferably all three can be placed in equidistant triangle of distance 5-7M. Connect the Satellite Transponder to the AC Mains and switch it 'ON' by mains switch. Connect the Downlink Receiver to the AC Mains and switch it 'ON' by mains switch. The Downlink Receiver Frequency can be changed from 2414-2432 MHz. Attach Antenna to the Downlink Receiver with BNC - BNC lead. Align both the Transmitter and Receiver Antenna's in line such that both are in parallel

alignment. Adjust transmitter uplink frequency to 2468 MHz and transponder receiver frequency

also to 2468 MHz. Keep Downlink Frequency of Transponder to 2414 MHz. Keep the Downlink Receiver 00 2414 MHz. Disable Tone mode for transmission. In this case only carrier will get transmitted from

Uplink Transmitter.


Observe the Carrier waveform on Spectrum Analyzer and measure Its power (It is power of Carrier and Noise without any input, say it "C1").

Now switch ''off'' the Transmitter and measure the power again (It Is power of noise, say it ''N'').

Now subtract amplitude of noise from previously received signal (Carrier noise), you can get actual Carrier signal amplitude (say it "C").

Calculate Carrier to noise ratio from the formula. Carrier +Noise Power (in dB) = C1 Noise Power (in dB) = N Carrier to noise ratio (In dB) = C = C1 - N

Calculation:

To calculate the carrier to noise ratio of established satellite link . Observe the Carrier waveform on Spectrum Analyzer and measure its power. It is power

of Carrier and Noise without any input, Cdbm = -35.3dBm


Now switch “OFF” the Uplink Transmitter and measure the power again. (It is power of Noise, Ndbm. = -99.8 dBm

The display gives the reading directly in terms of dB. Now to calculate Carrier to noise ratio proceed as follows

Calculation:

CNR Is a pre-detection measurement performed on RF signals. It Is the ratio of raw

carrier power to raw noise power. Technically speaking, when measuring CNR against real thermal noise, one actually Is measuring (C+N) / N.


CNR is generally accepted to be pre-detection measurement that is, one made at RF. Refer the figure as example only.

C/N ratios are often specified in decibels (dB):

CNRdb = 10log10 = Cdbm – Ndbm

Now we have recorded the reading in terms of dBm so

CNRdb = Cdbm - Ndbm = -35.3 dBm - (- 99.8dBm) = 60.5 dB

Carrier to Noise ratio (in numeric) = 25.15


Experiment: 9 Objective: To calculate signal to noise ratio of established satellite link Equipments Needed:

Uplink Transmitter Dish Antennas Satellite Transponder Downlink Receiver Oscilloscope connecting cables.

Procedure:

Connect the Satellite Uplink Transmitter to AC Mains. Switch 'ON the transmitter by Mains switch and frequency display will light up. The transmitting frequency can be selected by Frequency Select switch. The frequency

can be changed from 2450-2468 MHz. Connect Antenna to Uplink Transmitter with BNC -BNC lead. Place Downlink Receiver at a convenient distance of 5-7m. (It can go even up to 10m.). Place a Satellite Transponder between Transmitter and Receiver at a convenient

distance; preferably all three can be placed in equidistant triangle of distance 5-7m. Connect the Satellite Transponder to the AC Mains and switch It 'ON' by mains switch. Connect the Downlink Receiver to the AC Mains and switch It 'ON' by mains switch. The Downlink Receiver Frequency can be changed from 2414-2432 MHz. Attach Antenna to the Downlink Receiver with BNC - BNC lead. Align both the Transmitter and Receiver Antenna's in line, such that both are in parallel

alignment. Adjust transmitter uplink frequency to 2468 MHz and transponder receiver frequency

also to 2968 MHz. Keep Downlink Frequency of Transponder to 2414 MHz. Keep the Downlink Receiver to 2414 MHz. Now Select the Tone from "Channel Select B", so as to transmit tone signal from Uplink

Transmitter.


Make the Downlink Receiver in Tone mode with the help of "Channel Select B". Observe Tone Signal on Oscilloscope and measure its amplitude. (The received tone has

original signal and noise both, say it "S1"). Now change "Tone mode" to any other mode with the help of "Channel Select B" of the

Uplink Transmitter and again measure amplitude of received signal at Downlink Receiver (This signal have only noise, say it "N").

Now subtract amplitude of noise from previously received signal (Tone + noise), you can get actual tone signal amplitude (say it "S"). S = 51. – N

Calculate signal to noise ratio from the formula. Signal to Noise ratio = 5 / N Signal to Noise ratio (in dB) = 20 log S / N

Observation:

To calculate signal to noise ratio of established satellite link. Select 'Tone' mode at Uplink Transmitter and set the frequency pot to maximum

position and amplitude to 2Vpp. Observe the received 'Tone' signal at 'Received Tone' section of Downlink Receiver on

Oscilloscope and measure its amplitude. The received tone has original signal and noise both, say it 'S1'. Oscilloscope setting: CH1: 0.5V & Time Base: 0.1mS


Now at uplink Transmitter, change "Tone mode" to any other mode say 'MIC' mode using 'Channel Select B' key of the Uplink Transmitter and again measure amplitude of received signal at Downlink Receiver (This signal have only noise, say it "N").

Oscilloscope setting: CH1: 50mV & Time Base: 5uS

Calculation:

The signal-to-noise ratio express in decibels the amount by which a signal level exceeds its corresponding noise.

In the most general case, SNR express as the ratio of rms (root mean square) signal level, Srms, to the rms noise, Nrms,(SNR = Srms/Nrms).

SNR is generally accepted to be a pre-modulation or post-detection measurement that is one made on base signal.

Refer the figure as example only.


The received tone signal amplitude is 2Vpp. The received noise signal amplitude is 50mV approximately. Now subtract amplitude of noise from previously received signal (Tone + noise), you can

get actual tone signal amplitude (say it "S"). S = S1 - N = 2000mV - 50 mV= 1950mV

Calculate signal to noise ratio from the formula. Signal to noise ratio = S / N = 1950/50 = 39 Signal to noise ratio (in dB) = 20 log S / N = 31.82 Db


Experiment no: 10

Objective: To study the global positioning system and GPS receiver.

THEORY:-

The GPS system consists of a constellation of 24 satellites. While not officially declared fully operational, for all practical purposes the system is now fully operational. These satellites orbit the earth at an altitude of about 10,900 miles and at an inclination of 55 degrees. As I will demonstrate in my next column, this orbit translates to an orbital period of 12 hours. The orbits are distributed around the earth in such a way that at least 4 satellites are always visible from virtually any point on the surface of the earth. This provides a means of precisely determining the position of the user in longitude, latitude, and altitude. The satellites operate at two frequencies, known as L1 and L2. These two frequencies are 1575.42 MHz and 1227.6 MHz, respectively.

Fig 1. Constellation of GPS system

The whole system operates at a system clock frequency of 10.23 MHz, which is an exact submultiples of the L1 and L2 frequencies. The two transmission frequencies are modulated with a pseudo-random signal to produce spread spectrum signals. The L1 channel is modulated with both a 1.023 Mbps pseudo-random code known as the C/A (course/acquisition) code and a 10.23 Mbps PN code known as the P (precision) code. The L2 channel is only modulated with the P code. The two codes are considerably different in characteristics. The L1 code repeats every 1023 bits, or every 1 millisecond. The P code, on the other hand, only repeats itself every 267 days. Furthermore, the P code can be encrypted by the Department of Defense, so as to make it unavailable to civilian (or unauthorized) users. This limits the best accuracy obtainable by unauthorized users to about 30 meters, while allowing authorized users to achieve accuracies of up to 3 meters. Additionally, the DOD, at its discretion, can disseminate slightly inaccurate information pertaining to the location of the satellites, so as to further degrade the accuracy obtainable by unauthorized users to about 100 meters. These accuracy degradation


capabilities are important, since hostile nations could use the information against us in times of war. As time has gone by, however, more potential applications have been developed for GPS and many techniques have been developed to augment the accuracy available to unauthorized users. Techniques like carrier phase tracking and differential GPS can allow users to obtain centimeter level accuracy, especially in cases where measurements are being made at a fixed location. However, it is well established that even aircraft positions can be determined to an accuracy of better than several meters, even in real time. Other applications include moving map displays in cars and trucks. Attitudes of aircraft and spacecraft can also be determined with GPS. GPS equipment is currently set-up in the San Francisco area to allow researchers to measure the amount of shifting in the earth's surface during the next earthquake. GPS was also recently used to measure the height of Mount Everest and K2. Forest fire fighters use GPS to define the extent of fires and townships are using GPS equipped vans to map roads in a small fraction of the time that would be required for conventional surveying techniques.

Fig 2.Determining position using GPS

Determining Position

A GPS receiver "knows" the location of the satellites, because that information is included in satellite transmissions. By estimating how far away a satellite is, the receiver also "knows" it is located somewhere on the surface of an imaginary sphere centered at the satellite. It then determines the sizes of several spheres, one for each satellite. The receiver is located where these spheres intersect.


Signals In order for GPS to work, a network of satellites was placed into orbit around planet Earth, each broadcasting a specific signal, much like a normal radio signal. This signal can be received by a low cost, low technology aerial, even though the signal is very weak. Rather than carrying an actual radio or television program, the signals that are broadcast by the satellites carry data that is passed from the aerial, decoded and used by to the GPS software. The information is specific enough that the GPS software can identify the satellite, it’s location in space, and calculates the time that the signal took to travel from the satellite to the GPS receiver. Using different signals from different satellites, the GPS software is able to calculate the position of the receiver. The principle is very similar to that which is used in orienteering – if you can identify three places on your map, take a bearing to where they are, and draw three lines on the map, then you will find out where you are on the map. The lines will intersect, and, depending on the accuracy of the bearings, the triangle that they form where they intersect will approximate your position, within a margin of error. GPS software performs a similar kind of exercise, using the known positions of the satellites in space, and measuring the time that the signal has taken to travel from the satellite to Earth. The result of the “trilateration” (the term used when distances are used instead of bearings) of at least three satellites, assuming that the clocks are all synchronized enables the software to calculate, within a margin of error, where the device is located in terms of its latitude (East-West) and longitude (North-South) and distance from the center of the Earth.

Timing & Correction

In a perfect world, the accuracy should be absolute, but there are many different factors which prevent this. Principally, it is impossible to ensure that the clocks are all synchronized. Since the satellites each contain atomic clocks which are extremely accurate, and certainly accurate with respect to each other, we can assume that most of the problem lies with the clock inside the GPS unit itself. Keeping the cost of the technology down to a minimum is a key part of the success of any consumer device, and it is simply not possible to fit each GPS unit with an atomic clock costing tens of thousands of dollars. Luckily, in creating the system, the designers designed GPS to work whether the receiver’s clock is accurate or not. There are a few solutions. However the solution that was chosen uses a fourth satellite to provide a cross check in the trilateration process. Since trilateration from three signals should pinpoint the location exactly, adding a fourth will move that location; that is, it will not intersect with the calculated location. This indicates to the GPS software that there is a discrepancy, and so it performs an additional calculation to find a value that it can use to adjust all the signals so that the four lines intersect. Usually, this is as simple as subtracting a second (for example) from each of the calculated travel times of the signals.


Thus, the GPS software can also update its’ own internal clock; and means that not only do we have an accurate positioning device, but also an atomic clock in the palm of our hands.

Mapping

Knowing where the device is in space is one thing, but it is fairly useless information without something to compare it with. Thus, the mapping part of any GPS software is very important; it is how GPS works our possible routes, and allows the user to plan trips in advance. In fact, it is often the mapping data which elevates the price of the GPS solution; it must be accurate and updated reasonably frequently. There are, however, several kinds of map, and each is intended for different users, with different needs. Road users, for example, require that their mapping data contains accurate information about the road network in the region that they will be traveling in, but will not require detailed information about the lie of the land – they do not really worry about the height of hills and so forth. On the other hand, hiking GPS users might wish to have a detailed map of the terrain, rivers, hills and so forth, and perhaps tracks and trails, but not roads. They might also like to adorn their map with specific icons of things that they find along the way and that they wish to keep a record of – not to mention waypoints; locations to make for on their general route. Finally, marine users need very specific information relating to the sea bed, navigable channels, and other pieces of maritime data that enables them to navigate safely. Of course, the sea itself is reasonably featureless, but underneath quite some detail is needed to be sure that the boat will not become grounded.

Fishermen also use marine GPS to locate themselves and track the movement of shoals of fish both in real time, and to predict where they will be the next day. The advent of GPS fixing has also meant that co-operative fishing has become much easier, where there are several boats all relaying their locations to each other while they locate the best fishing waters. Special kinds of marine GPS, known as fish finders, also combine several functions in one to help fishermen.

GPS Accuracy

The accuracy of a position determined with GPS depends on the type of receiver. Most hand-held GPS units have about 10-20 meter accuracy. Other types of receivers use a method called Differential GPS (DGPS) to obtain much higher accuracy. DGPS requires an additional receiver fixed at a known location nearby. Observations made by the stationary receiver are used to correct positions recorded by the roving units, producing an accuracy greater than 1 meter. When the system was created, timing errors were inserted into GPS transmissions to limit the


accuracy of non-military GPS receivers to about 100 meters. This part of GPS operations, called Selective Availability, was eliminated in May 2000.

GPS Receiver:-

The Global Positioning System (GPS) works on the principle that if you know your distance from several locations, then you can calculate your location. The known locations are the 24 satellites located in six orbital planes at an altitude of 20,200Km. These satellites circle the Earth every 12 hours and broadcast a data stream at the primary frequency L1 of 1.575GHz which carries the coarse -acquistion (C/A) encoded signal to the ground. The GPS receiver measures the time of arrival of the C/A code to a fraction of a millisecond, and thus determines the distance to the satellite.

Fig 3. GPS Receiver


The Core Subsystems include: Front End The GPS L1 signals (Maximum = 24 signals) at 1.575GHz are received at the antenna and amplified by the Low-Noise-Amplifier (LNA). The RF front-end further filters, mixes, and amplifies (AGC) the signal down to the IF frequency where it is digitally sampled by an ADC. Baseband Processor/CPU The ADC samples of GPS C/A code signals are correlated by the DSP and then formulated to make range measurements to the GPS satellites. The DSP is interfaced with a general-purpose CPU, which handles tracking channels and controls user interfaces. TI OMAP integrates both DSP and ARM processor on the same chip. Memory The processor runs applications stored in memory. The OS is stored in non-volatile memory such as EE/FLASH/ROM. Applications may be loaded in FLASH or DRAM. User Interface Allows user to input/output data from the receiver using input commands via microphone, touch screen, and output MP3 to the earplug. Connectivity Allows the receiver to connect to the USB port. Conclusion:

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