MIDDLE EAST TECHNICAL UNIVERSITY

ELECTRICAL AND ELECTRONICS ENGINEERING

DEPARTMENT

EE300 SUMMER PRACTICE REPORT

STUDENT NAME: OKAY ARIK STUDENT ID#: 144281-3 SP DATE: 18.06.2007 – 13.07.2007 SUBMISSION DATE: September 15, 2007 STUDENT CONTACT INFORMATION: PHONE NUMBER: 0.505.959 66 57 E-MAIL ADRESS: okayarik@gmail.com THE COMPANY: TRT (Turkish Radio and Television Corporation) COMPANY DIVISION: ARIM (Research and Production Division) COMPANY LOCATION: Turan Guneş Boulevard OR-AN, ANKARA COMPANY PHONE AND E-MAIL: (0-312) 490 17 86, arim@trt.net.tr RELATED FIELD: TELECOMMUNICATIONS, SIGNAL PROCESSING

TABLE OF CONTENT

1. DESCRIPTION OF THE COMPANY......................3

1.1 COMPANY NAME ................................................................................................... 3 1.2 COMPANY LOCATION ................................................................................................ 3 1.3 ORGANIZATIONAL STRUCTURE.............................................................................. 5

1.3.1 Organizational Structure of TRT.................................................................... 5 1.3.2 Organizational Structure of ARIM................................................................. 6

1.4 NUMBER AND DUTIES OF ENGINEERS EMPLOYED............................................ 6 1.5 MAIN AREA OF BUSINESS ......................................................................................... 6 1.6 A BRIEF HISTORY OF THE COMPANY ....................................................................9

2. INRODUCTION......................................................10

3. RF (RADIO FREQUENCY) FILTER .....................11

3.1 WHAT IS RF (RADIO FREQUENCY) ........................................................................ 11 3.2 FM TRANSMITTER ..................................................................................................... 12 3.3 PASSIVE BAND – PASS FILTER ............................................................................... 14

3.3.1 Structure of the Filter....................................................................................... 14 3.3.2 Measurement of the Filter............................................................................... 15 3.3.3 Reformation of Cylindrical Inductors.......................................................... 17

4. CONCLUSION........................................................20

5. REFERENCES.........................................................21

6. APPENDIX..............................................................22

1. DESCRIPTION OF THE COMPANY

1.1 COMPANY NAME

TRT (Turkish Radio and Television Corporation)

1.2 COMPANY LOCATION

TRT Headquarters which include the division where I performed my summer practice,

ARIM, is in Oran on the Turan Guneş Boulevard. Its adress is:

Turan Guneş Boulevard OR-AN, ANKARA

Fig 1.1

TRT Headquarters and ARIM Division Building

Fig 1.2

Fig 1.3

1.3 ORGANIZATIONAL STRUCTURE

1.3.1 Organizational Structure of TRT

Fig 1.4

1.3.2 Organizational Structure of ARIM

Fig 1.5

1.4 NUMBER AND DUTIES OF ENGINEERS EMPLOYED

14 engineers, 28 technicians, 4 experts, 3 masters and 16 administrative staff members

whose total number is 65, are employed in ARIM. Most of these engineers works in

Directorate of Development Laboratory, in engineering groups.

1.5 MAIN AREA OF BUSINESS

ARIM (Research and Production Division) products various devices used by TRT,

realizes research and development activities of the company, and also sells its products to

other companies. ARIM is the unique producer of many devices produced by the division.

SOME PRODUCTS OF ARIM *

• Clock System: A clock system which are connected to main clock by radio signals.

Main clock synchronize itself via BBC to World Clock System. (Fig 1.6)

Fig 1.6

• Clock Beep Generator: It generates 0.5 second long 1kHz beeps at every hour and

half hour by the information generated by main clock. When the signal which comes

from main clock, it generates “no information” warning signal. (Fig 1.7)

Fig 1.7

• DAB Project: After FM strereo radio broadcasting, the most important development

in radio technology is DAB (Digital Audio Broadcasting) technic. DAB provides

broadcasting sound and data in 6 programs with a single transmitter in the quality of a

CD. In order to follow these developments in the world, in 2002, ARIM started to

experimental broadcasting on VHF 12B channel in Ankara.

• KAMOK: During broadcasting, speaker read the text which will be read from this

device. Therefore the speaker never lose eye-contact with the audience. The device

has all editing properties in Windows Word program.

• FM Transmitter: It is designed for high quality radio broadcasting. Running interval

of the device is between 87,5 and 108 MHz. (Fig 1.8)

Fig 1.8

• Mic/Line Dividing Amplifier: It amplifies each of 16 channel microphone and line

input signals to 4 output signal with arbitrary values.

• Sound Amplifiers and Loudspeaker: ARIM products various sound amplifiers

having different properties and active and passive loudspeakers.

• EBU Reporter Device: This device is used to communicate reporters and

commentators to broadcasting studio on telephone line in sport matches and some

organizations. It is acceptable to criterias of EBU (European Broadcasting Union).

(Fig 1.9)

Fig 1.9

1.6 A BRIEF HISTORY OF THE COMPANY

TRT (Turkish Radio and Television Corporation) was founded in 1964 as an

autonomous establishment in order to realize the national public radio and television

broadcasting of Turkey. The first programmed radio broadcasting was realized in 1965 and at

the news time all the radios were connected to Ankara Radio. In 1968, the first experimental

television broadcasing was realized. In 1972, by broadcasting Munich Summer Olympics,

TRT broadcasted live from a foreign country first time. In 1974, television broadcasting

reached to seven days for a week. All the radios of Turkey started to be broadcasted in the

name of “TRT 1” for twenty four hours. In 1975, 20th Eurovision Song Contest which TRT

participated first time was broadcasted live from Stockholm. In 1976, the first full color

television broadcasting was realized. After 1984, whole television broadcasting of TRT was

full color. In the same year, radio broadcasting became stereo. In 1986, TRT 2 and in 1989,

TRT 3 – TRT GAP started to broadcasting. In 1990, teletext broadcasting which is called

“ telegün” started. In the same year, TRT 4, in 1992 TRT-INT-AVRASYA started to

broadcasting.

Like many broadcasting companies, TRT founded a research laboratory starting to

production in 1968. In 1976, this research laboatory became Research and Production

Division (ARIM – in turkish first two letters of the words “araştırma” and “imalat”). Before

1989, ARIM has producted 10W and 50W television transmitter and antennas. However, after

this year, production and management of television transmitters are entrusted to PTT.

Therfore, since 1989, the division focused on production of radio transmitters and devices

used in television and radio studios. Today, ARIM products various devices used by TRT,

realizes research and development activities of the company, and also sells its products to

other companies. The aim of the activities of ARIM is high technology, high performance and

satisfaction of users.

2. INRODUCTION

I have performed my first summer practice TRT (Turkish Radio and Television

Corporation), which is the national public broadcaster of Turkey. Today, TRT broadcasts

from 7 distinct TV channel and 6 distinct radio channel for 24 hours in a day. My practice

lasted totally four weeks starting from 18.06.2007 and ending in 13.07.2007. The division

where I performed my practice is ARIM (Research and Production Division) which designs,

develops, and produces some of devices used in broadcasting. During my summer practice,

we measured and regulated RF filters designed by ARIM. These are band pass filters which

allow to pass signal whise frequencies are between 88 and 108 MHz. We measured filters

with impedance analyzer. While regulating filter, we reformed cylindrical inductors of the

filter.

3. RF (RADIO FREQUENCY) FILTER

3.1 WHAT IS RF (RADIO FREQUENCY)

RF is a kind of communication technology. It works with a transmitter and a receiver

circuits designed in order to transmit and receive the electromagnetic wave having a specific

frequency. Sensitivity of the transmitter and the receiver depends on the distance which

enables communication. For long range communication, such as television and radio

broadcasting, transmitter has high power output. Ontheotherhand, for short range

communication, such as bluetooth, low power output is enough to communicate. Objects

between transmitter and receiver do not blocks communication in this technology thanks to

penetration property of RF. In contrast, some tecnologies such as infrared, this is a serious

problem. In RF tecnology, datum are coded in a specific frequency spectrum and the reveiver

receives this signal by being modulated in this frequency spectrum. Radio frequencies are

restricted for specific aims by the government (fig3.1). For example, FM radio broadcasting

uses spectrum of 88-108 MHz, cell phones use spectrum of 900-1800 MHz, and bluetooth,

wireless communication technology use spectrum of 2.4 GHz.

Fig 3.1

3.2 FM TRANSMITTER

This is a kind of transmitter which generates frequency modulated signals. They

generates sinusodial signal with stable amplitude. Frequency of the signal varies according to

the datum. A non-modulated signal has stable frequency and this is called “center frequency”.

While being modulated, frequency of output signal varies and become greater or smaller than

central frequency. Wheather or not output signal is modulated, amplitude of output signal is

stable (Fig 3.2).

Fig 3.2

The number and type of circuits used in a FM transmitter varies according to the

characteristics of output signal. However, there are some circuits which are common for all

FM transmitters. In fig 3.3, a simple FM transmitter circuit which includes all the necessary

parts is shown. This circuit consists of a oscillator, a FM modulator, buffer and RF power

amplifier.

Fig 3.3

In this circuit, the non-modulated signal generated by oscillator has central frequency.

When the modulation was applied, frequency of output signal of oscillator varies according to

the frequency of applied signal to oscillator. Infact, the signal applied to the circuit by

modulator is capacitive or inductive reactance. The type and value of rectance applied to

oscillator by modulator depends on amplitude of input signal of modulator. Therefore,

frequency of output signal of oscillator varies acording to amplitude of input signal of

modulator. Modulated output signal of oscillator passes through buffer amplifier and applied

to RF power amplifier. Here, buffer amplifier does not only isolate output signal of oscillator

from RF power amplifier but also amplifies the signal. RF power amlifier amplifies the

output signal of buffer amplifier in order to make the signal enough powerful to broadcast.

3.3 PASSIVE BAND – PASS FILTER

Engineers of ARIM has designed a passive band-pass filter. This designed circuit has

been mass-produced in another company. Our mission was testing these circuits that they

have acceptable values or not. Moreover we should have also reform cylindrical inductors by

pulling or pushing in order to make small changes to their inductance values. First of all, I

have to mention some concept about filters and inductors.

3.3.1 Structure of the Filter

We know that requency band used in radio signals is between 88 and 108 MHz. This

circuit was designed in order to allow the signals having frequency between 88 and 108 MHz

and stop the signals having frequency below 88 MHz and above 108 MHz. Circuit diagram of

this filter is shown below (Fig 3.4).

Fig 3.4

The circuit consists of three cylindrical inductors and more than three capacitors which

are parallel connected. In fig 3.4 a simplified version of the circuit is shown. For capacitors,

chip capacitors are used (fig 3.5). Chip capacitors are rectangular prism shaped element

whose terminals are two opposite side of the prism. They have no wire as other capacitors

used in electronics therefore there is no need to pierce the circuit card. Consequently,

production cost is minimized. Moreover they are used in high frequencies as RF technology.

Chip Capacitors

Fig 3.5

3.3.2 Measurement of the Filter

We realized the measurements with a impedance analyzer. This device can measure

and plot transfer function of the measured circuit in given frequency band without any aid of

external hardware as we do in the course EE214. However, values of transfer function is in

logatitmic scale (bode plot) and measured in decibel (dB). We know that in a filter, half

power point are main parameters. At these points, power is half done therefore voltage

becomes its one over squareroot of two. Because power is direct proportional to square of

voltage.

H( fc) (in dB) = 20 log [Vo ( fc) / log V in ( fc)]

= 10 log [Vo2 ( fc) / log V in

2 ( fc)]

= 10 log [ ½ ] = -3.0103 ≈ -3

For this reason, we focused –3 dB value for a bit above 108 MHz and a bit below 88

MHz. Furthermore, between 88 and 108 MHz transfer function should not be excess small. In

Electronics Workbench program, bode diagram of the filter is below (fig 3.6-7-8). The graphs

we observed in the impedance analyzer is smilar with this graph. Nevertheless, the graphs we

observed is not as rigid as the graph drawn by the program.

Fig 3.6

Fig 3.7

Fig 3.8

3.3.3 Reformation of Cylindrical Inductors

I had mentioned our reforming cylindrical inductors by pulling or pushing them in

order to change the inductance values of them. Therefore, we will have obtain remarkable

chances in bode diagrams of the filters. Consequently, this necessitate to mention briefly

inductance of a cylindrical inductor (solenoid).

A Solenoidal and Magnetic Field Created by Current

Fig 3.9

A solenoid is a helix shaped wire designed for a remarkable inductance. It is accepted

that magnetic field created by the current passing through the solenoid is focused

homogenously inside of the cylinder envelopes the solenoid (fig 3.9). Moreover, outside of

the cylinder, magnetic field is neglectable. This is a good property to use in electronic circuits

in order to avoid affect of coils each other as mutual conductors. In addition, this fact gives us

an easiness to calculate the inductance of solenoid. In theorical calculation, we designed a

loop passing through the solenoid linearly, and arrives its end on a arbitrary path outside the

cylinder we mentioned (fig 3.10).

Fig 3.10

On the path c, we apply Ampére’s Law: "c B·dl = B l = µ0 nI, here n is the number of

turns. Therefore, B = µ0 nI / l .

By the Faraday’s Law of Induction: V = n A dB/dt = µ0 n2 A (dI/dt) / l = L(dI/dt), here

A is the base area of the cylinder we mentioned above.

Briefly, the inductance of the solenoidal L = µ0 n2 A / l . Consequently, the inductance

is inversely proportional to l, the length of solenoidal.

However, in practice, we did not mind these theorical calculation. I wanted to show

that length of the sinusodial is a variable of the inductance above. We applied arbitrary

operations on cylindric inductors. When we reached a satisfactory bode diagram whose I

mentioned proficiency criteria in the part titled “Measurement of the Filter”, we stoped and

passed next circuit.

4. CONCLUSION

At the beginning of my summer practice, we took a trip in broadcasting studios of

TRT. We saw analogue and digital studios.

In the first two weeks of my summer practice, I was sat in the digital lab. It is told me

that an engineer studying on microcontroller programming was in an education program and

he would come. Hence, I would have contributed in microcontroller programming works.

Nevertheless, that was not realized. Consequently, in the first two week, I did not participate

in engineering works except for some repairings. However, I studied on programming

“PIC16F84” and the programming language “assebly”.

One of these repairings was on a control part of the radio transmitters. Inside this

device, there is a modem sending signals via GSM as cell phones and informs that the

transmitter run regularly or not. The problem was on the LCD panel and replacing it was

enough to solve the problem. In order to get a new LCD panel we went to “the store” which is

managed by Directorate of Reserve Control and Store Branch mentioned in the part titled

“Organizatioan Structure of ARIM” (fig 1.5). In the store, there is spare parts of all

components of products of ARIM. Every component has a code which makes finding wanted

part easier. During two weeks, I have also done some office works. For example, I made a list

of scrap office and laboratory materials.

In the second half of my summer practice, I was in RF laboratory. Here, I participate

jobs mentioned in the part titled “RF (Radio Frequency) Filter”. While we measure RF filters,

we did not use crocodiles or probes in order to connect the RF filter to impedance analyzer.

While connectining filters, we soldered input and output cables to the filter. Hence, we gained

pratique of soldering. This is a harder way of connecting nevertheless this method gives more

clear results.

During my summer practice, I participated a lecture on digital television broadcasting.

The lecturer was a representative of a private foreign company. He told different technologies

on digital broadcasting.

5. REFERENCES

• http://www.trt.net.tr • http://en.wikipedia.org/wiki/Turkish_Radio_and_Television_Corporation • http://en.wikipedia.org/wiki/Frequency_modulation • http://www.tpub.com/content/et/14086/css/14086_38.htm • http://news.thomasnet.com/fullstory/13303 • http://members.wri.com/jeffb/visualization/solenoid.shtml • http://www.physics.sjsu.edu/becker/physics51/mag_field.htm

6. APPENDIX

* Catalogue of the Products of ARIM