cdr2(sajjad tarahomi)

Career Episode 2 RDS Encoder

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RDS Encoder

Introduction CE2.1

Designing and Construction of RDS modulator was one of my valuable experiences in TAKTA Company that I did it in 2011 and it was developed in 2012. New version with more features and new options ended in 2011 and now it’s ready for industrial productions after prototyping production, debugging in software and hardware. I have tried to give a good overview about RDS system in broadcasting with related software and hardware and my experience about this part of FM Transmitter.

Background The nature of overall engineering project: CE 2.2

RDS (Radio Data System) is a protocol for transferring digital information in conventional FM (or VHF) broadcast over regular audio programs. This information include date and time, advertising and other text messages, and perform additional ID, control and housekeeping functions. On the other hand RDS offers the possibility for data service provider to introduce new data services to many users. Thus RDS can accommodate a wide range of possible implementation options.

Physical layer of RDS system Method of modulation CE 2.3 The subcarrier is amplitude modulated by the shaped and bi-phase coded signal. The subcarrier is suppressed. This method of modulation may alternatively be thought of as a form of two-phase shift keying (PSK) with a phase deviation of ± 90 degrees.


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The source data at the transmitter are differentially encoded using below table:

Where 𝑡𝑡𝑖𝑖 is some arbitrary time and 𝑡𝑡𝑖𝑖−1 is the time one message-data clock period earlier, and where the message-data-clock rate is equal to 1187.5 Hz. Thus when the input level is 0, the output remains unchanged from the previous output bit, and when an input 1 occurs, the new output bit is the complement of the previous output bit. Baseband coding CE 2.4 Figure below shows the structure of the baseband coding. The largest element in the structure is called a “group” of 104 bits. Each group comprises 4 blocks of 26 bits. Each block comprises an information word and a check word. Each information word comprises 16 bits and each check word comprises 10 bits.


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Objectives to be achieved with RDS Features CE 2.5

The following fields are some features in RDS system:

- AF (Alternative Frequency) This option allows a receiver to retune to a different frequency providing the same station when the first signal becomes too weak. That is, RDS receivers (e.g. car radio receivers) search for the best signal that carries the same program with no audible interruption.

- CT (Clock Time) RDS is capable of setting the date and time on RDS receivers equipped with a clock. Using of this option is arbitrary.

- PS (Program Service) This is the station’s name that might typically appear on the receiver faceplate display. PS can be up to eight characters in length and can be as simple as the station’s call letters. For long message transferring, RDS use dynamic PS, that is, it sends long message in a succession of eight character frames.

- PTY (Program Type) This data flag identifies the station format from a list of pre-assigned categories. Many RDS receivers are able to seek the listener’s preferred listening preference automatically. This helps a broadcaster catch a certain transient audience share …

- RT (Radio Text) This is a 64-character block of plain text that the listener is able to select for visual display, but on only those radios that have an INFO or TEXT button. The RT is not typically available on automobile receivers for legacy safety considerations.

- TMC (Traffic Message Channel) Traffic information can be send by RDS. It is often available for automotive navigation systems. In many countries only encrypted traffic data is broadcast, and so an appropriate decoder, possibly tied to a subscription service, is required to use the traffic data.


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The nature of my particular work area: CE 2.6 The RDS project was done in TAKTA Company and was divided into different parts: Designing the overall block diagram, Designing the schematics and circuits, analyzing different parts of the circuits, Assembly, Connecting different parts together, constructing, programming and finally testing and optimizing it. Designing the circuits, programming and analyzing it, was my particular work in this project as an electronic-communication engineer. I was also regularly controlling the progress of the project and was responsible for different stages of construction. It was a golden opportunity for me to increase my project management abilities and skills to professionally utilize the resources of the project. A chart of the organizational structure highlighting my position: CE 2.7 TAKTA Electronic Research and Production Company have three main divisions: Business Department, Technical Department and Financial Department. The Research and Development (R&D) Section is a Technical division.


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TAKTA Electronic Research and

Production Company

Financial SectionTechnical SectionCommercial Section

Research and Develeopment

(R&D)Production Section Technical Support

Suppervisor

Technical Engineer Technician (Mountaging)Quality Control

I have been working as an Electronic and Microwave Engineer in the Research and Development Department (R&D). My job includes designing, simulation, optimization and test of different electronic and communication circuits. I have designed the main passive parts of digital UHF Transmitters and High Power FM Transmitter(for example: combiner, splitter, sampler, directional coupler, different types of adaptors and connectors, impedance matching circuits and etc.) and some electronic and active parts of UHF Digital transmitters and FM Transmitter (for example: High power amplifier, AGC, Drive Amplifier, RDS Encoder and etc). At the first stage I design and simulate circuits with related software (for example: ADS, CST Microwave office, HFSS, DXP and etc). After an optimization and simulation, I draw its PCB with Alitium2004 software. Then these Circuits Boards files are sent to print. After the print, I usually assemble different elements on the PCB and test it with different advanced Electronic Measurement instruments. At the end of the process, I usually write a complete report and documentation about my work to be able to have a useful background from my jobs in the future.


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A statement of my duties: CE 2.8 I was responsible to: - Design the Block diagram of different parts of the project. - Design, Simulation and programming of the circuit of the project (with related software). - Assembling, test and Correction of the PCB. - Supervise on each step of my tasks and finalize the construction. - Manage the team and control the project progress steps.

Personal Workplace Activity CE 2.9

Leading features of my board include: . All of groups in RDS (EN50067 standard) supported. . UECP protocol supported (it use for RDS parameter control in network) . Offers RS232, RS485 serial and TCP/IP connectivity . The front-panel LCD screen and keyboard for local data entry without computer using . A build-in scheduler can automatically transmit RDS commands based on date & time . Embedded web server (HTTP) .Convenient loop-through or side-chain operation with any exciter/stereo coder combination . Software adjustable amplitude and phase of output signal . High security and conditional access for network data entry . Huge memory for data bank saving . Software development by customer ordering


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Strategies devised by me including any original or creative design work

CE 2.10

I designed and assembled the below circuit according to the purposes of the project and my electronic engineering studies.

Technical Specifications:

My project technical parameters are summarized in below table:

RDS Signal

Differential & Biphase Coding DSSC Modulation 57 KHz±6Hz Center Frequency ±2.4 KHz Band Width

0-2500mv p-p (5mv Step) Level

0-360 (6˚ Step) Phase

Internal or External(Automatic Switching) Synchronization

Un balanced Output Type

Interface

RS232 , RS485 (DB9) Serial

Full duplen 10/100 M Base-T (RJ45) TCP/IP

2 opto – isolation & 1 relay (DB9) I/O

MPX or 19KHz in (BNC) Connector In

RDS Out (BNC) Connector Out

RDS Features

PS-PI-TP-TA-PTY-PTYN-MS-DI-RT-CT-AF-EON-EWS-IH-TMC-TDC-PIN-SLC-LINK-FFG-ODA


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Block diagram CE 2.11 Below figure is a simplified block diagram of my board. As a brief description, output signal is produced in CPU2 after D/A (Digital to Analog conversion) and filtering with gain control process. It may be added to MPX input signal if you need or send to output connector directly. Synchronization signal (114 KHz clock) can be constructed in TIMEBASE unit internally or may be extracted from input signal by filtering and other process in PLL unit. CPU2 acts as a communicator with other devices via serial port and LAN port. It processes all of the information and then it sends the results to CPU1. Input signal will be send to output connector without any change via bypass relay when there is any problem in the board or if encoder power is lost. On the other hand, there is a RTC chip (Real Time Clock) with battery backup in my board for date and clock synchronization.

CPU2

CPU1

3 bi

t

D/A GainControl

57 KHzBPF D/A

Rectifier

12 bit

∑

Rectifier

+5 V

Bypass Relay RDS/MPXOutput

Side/LoopSwitchPilot/MPX

Input

19 KHzBPF

PLL

LOCK

114 KHz Clock

Time Base114 KHz Clock

SPI

LAN Processor 3 bit

SPI

Interupt

Clock

RJ45 LCD

Key Pad

LED

I/O

DB9

EEPROMRTC

BAT

RS232

DB9

RS485

DB9

Block Diagram


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Circuit Description: CE 2.12

Circuit descriptions refer to the next two pages schematic diagram. Stereo pilot recovery- a sample of MPX signal is filtered by the band pass configuration of op-amp U8 (TL072 from TI) to recover the 19 KHz stereo pilot. Tone decoder U14 (LM567 from national) lends further filtering action and squares up the 19 KHz waveform. PLL unit consists of U10 (CD4046) and U11 (CD4018), the output of PLL unit is a 114 KHz square wave six times multiplication of the stereo pilot. This is a clocking that is used by digital processing stages to generate the RDS subcarrier. RDS waveform synthesis- U7(DSPIC33FJ128GP804 from Microchip) is a high speed microprocessor with onboard memory and other useful subsystems. The function of this unit is to synthesize the RDS waveform. This chip has an on-board crystal oscillator to establish an internal master clock for RDS waveform generation if the stereo pilot is not obtained. Digital subcarrier waveform are sent to D/A chip U6 (DAC902 from TI) for digital to analog conversion. Band-pass filter and combining stage- the segmented RDS waveform from the D/A chip is passed through dual band pass filter stages, U4 (TL072 from TI). This 57 KHz filter removes higher order distortion components. U3 (AD817 from AD) is a unity gain output driver stage for combining. with switching K1 in side chain mode , only the RDS subcarrier will be passed at combining stage to the output connector. With switch K1 in loop through operation, MPX signal applied to MPX input connector will be added to RDS subcarrier and combining signal will appear at output connector. Encoder data formatting- U20(DSPIC33FJ256GP710 from microchip) is a second microprocessor that is responsible for receiving and formatting all incoming RDS data. This chip is able to interface directly with the LAN port, U23 (ENC424J600 from microchip), and RS-232 serial interface, U16 (MAX232 from maxim), and RS485 interface, U18 & U19 (MAX 485 from maxim). U20 also addresses the LCD display and receive menu commands from the keypad.


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My engineering knowledge and skills in this project CE 2.13 Software consideration Proteus- I have used this software for some hardware parts such as filters, buffers and amplifier simulation after first designing. Protel DXP- I used this one for PCB (Printed Circuit Board) preparation. The last and final PCB was provided after three times by prototype debugging and board development. Next picture is a sample layer of my board. This board was constructed on 2-layer FR4 board.

Microsoft office Front page- by notice that my board acts as web server, I need to design some web page for all RDS parameter setting and monitoring. This software is like as other HTML programming software. For example, you can see code and final related web page below.


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My project programming code: ~inc:header.inc~ <div class="result fail" style="display:~status_fail~">Error: ~err_cont~</div> <form method=post action=dpsrt.htm name=dpsrt> <input type=hidden id=kka name=kka> <table class="one"> <caption><h1>Dynamic PS & RT</h1></caption> <thead><tr><th><br/>DPS buffer: <input type=radio name=dps value=1 checked>Cyclic <input type=radio name=dps value=3>del <input type=radio name=dps value=4>del All <input type=button name=set value=update onclick=subcheck(1)> </th></tr> </thead> <tbody><tr><td><div class=scrollarea style="height: 100px; width:99%;"> <table width=96% id=test onclick="ROW()"> <thead><tr><th width=10%>DPS No.</th><th width=85%>Content</th></tr></thead> <tbody> <tr><td>01</td><td>~da(0)~</td></tr> <tr><td>02</td><td>~da(1)~</td></tr> <tr><td>03</td><td>~da(2)~</td></tr> <tr><td>04</td><td>~da(3)~</td></tr> <tr><td>05</td><td>~da(4)~</td></tr> </tbody></table></div></td></tr> <tr><td>No.:<select id=dpn name=dpn></select> <input type=text name=ddd style=width:85%></td> <tr><td>Repetition(1-5):<input type=text name=psr value=~db~ size=1> Scrolling speed:<select name=dss> <option value=30 ~dc(0)~>Low</option> <option value=20 ~dc(1)~>Normal</option> <option value=10 ~dc(2)~>Fast</option> </select> Scrolling char(1-8):<input type=text name=psc value=~dd~ size=2 maxlength=1> </td></tr> <thead> <tr><th> RT buffer: <input type=radio name=rts value=1 checked>Cyclic <input type=radio name=rts value=3>del <input type=radio name=rts value=4>del All nbsp; <input type=button name=set value=update onclick=subcheck(2)> </th></tr></thead> <tr><td><div class=scrollarea style="height: 100px; width:99%;"><table width=96%> <thead><tr><th width=9%>RT No.</th><th width=80%>Content</th></tr></thead> <tbody> <tr><td>01</td><td>~de(0)~</td></tr> <tr><td>02</td><td>~de(1)~</td></tr> <tr><td>03</td><td>~de(2)~</td></tr> <tr><td>04</td><td>~de(3)~</td></tr> <tr><td>05</td><td>~de(4)~</td></tr> </tbody></table></div></td></tr> <tr><td>No.:<select id=rtn name=rtn></select><input type=text id=rt1 name=rt1 onkeydown=RTBoxes()></td></tr> <tr><td>Repetition(1-5):<input type=text name=rtr value=~df~ size=1 maxlength=1> Group version:<select name=rtg> <option value=0 ~dg(0)~>A type</option> <option value=1 ~dg(1)~>B type</option> </select> RT A/B flag:<select name=rtf>

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<option value=0 ~dh(0)~>ON</option> <option value=1 ~dh(1)~>OFF</option> </select> </td></tr> </tbody> </table><br/></form></div> <script language="javascript">  </script> ~inc:footer.inc~


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Web Page

Mplab- this is a C compiler from Microchip Co. main part of program in relation with CPU1 and

CPU2 was written in this environment. All of programs were implemented on their Flash memory. Any particular difficulties /problems I encountered and how I solved them CE 2.14 Hardware consideration All of main parts of hardware were installed and tested separately. By this step by step procedure, I could debug and solve some problem like these: Regulator temperature- at the first design, I used only one regulator to supply 3,3v to CPU1 and CPU2 and some other components. It became hot after 15 minutes working. So I decided to use two regulators for CPUs separately. Then they work in better conditions and I got good noise reduction additionally. LAN fail- when we connect to board via Ethernet port, some packet will be lost. I reduced the data transfer speed but I could not solve the problem, so I understood that there is no software


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problem. I checked the hardware, by try and error and changing the capacitance of related crystal oscillator, I could solve this problem (by using of 10pF capacitor instead of 20pF). RTC fail- CPU1 had not good performance and worked slowly in final board checking. When I checked it , I saw that RTC chip (PCF8593) interrupt the CPU1 in one second interval except one minute. That is, CPU was very busy for RTC chip interruption. I changed this chip by new and original one, so it worked properly. How I worked with other team members CE 2.15 Team working was important factor in my achievement to the progress. Apart from exclusive design related activities done by me, I was responsible for all stages of the project procedure. I had very friendly relationship with all team members. I prepared project schedule and determined each member task. I carefully followed and updated schedule based on the reports given by project team members. I collected very useful information from other experienced engineers and different books and web sites to increase my technical knowledge and share all information with other team members. There was not any conflict between team members because I tried to clearly define all tasks of project. In a word it was very successful team working and I earned many practical and valuable experiences during the project progress.

Summary My view of the overall project CE 2.16 RDS project was one of the best and high tech projects of TAKTA Company which I did it with the help of other team members. I considered many different factors in this project. For example I selected my necessary Electronic and Mechanic elements according to their quality, prices and their accessibility. Many costumers before this project and our RDS Encoder product, were complaining about the minor quality and high price of other similar RDS Encoder systems which had been produced. After finishing the project, customer feedback showed a significant rise in the customer satisfaction. To sum up, it was very successful project both in technically and financially view.


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How my personal role contributed to the project CE 2.17 Before the starting the project I spent a considerable time on gaining more information about different types of RDS Encoders. I studied different related books, surfed the web and talked to expert engineers about this subject. Finally according to collected information and other important factors (financial, accessibility, quality, features and etc) I designed the best block diagram for this project. In addition my knowledge about the designing and analyzing electronic circuits and equipment specifications helped the project to be successful considerably.

cdr2(sajjad tarahomi)

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