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ELEKTRONIKA TELEKOMUNIKASI
Universitas Mercu Buana
Fina Supegina, ST, MT
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Tujuan Komunikasi Radio
Mengirimkan informasi dari sumber ke
tujuan (dapat berjauhan letaknya) dengan
memanfaatkan media udara sebagaisaluran transmisi
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Bagan Komunikasi Radio Secara Umum
SUMBER TUJUAN
PEMANCAR (TX) PENERIMA (RX)
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Bagian TX dan RX Tersusun Atas Bagian-bagian Berikut
Pemancar (TX)
SUMBER MODULATOR
OSCILLATOR
PENGUAT
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Penerima (RX)
PENGUAT DEMODULATOR TUJUAN
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Jika diperhatikan lebih lanjut,maka terdapat beberapa hal yangmenjadi perhatian, yaitu :
Modulator dan Demodulator (Detector)
Oscillator
Penguat
Modulasi (akan dibahas tersendiri) Antenna
Saluran Transmisi
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Modulator
Berfungsi untuk memodifikasi sinyalpembawa (carrier) dari oscillator sesuaisistem modulasi yang digunakan
(pemodulasi)
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Demodulator (Detector)
Berfungsi sebagai alat untuk mendapatkaninformasi yang terkandung dalam sinyalcarrier termodulasi
Rangkaian Demodulator tergantung jenismodulasi yang digunakan
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Oscillator
Berfungsi sebagai Pembangkit SinyalPembawa (Carrier) pada Pemancar
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Penguat (Amplifier)
Berfungsi memberikan penguatanterhadap sinyal yang akandikirim/diterima
Pada penerima, dapat berfungsi sebagaifilter karena karakteristik responsefrequency mirip band pass filter
Pada pemancar, berfungsi mengjilangkanharmonisa dari rangkaian-rangkaianpemancar
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Antenna
Berfungsi meradiasikan gelombangelektromagnetik terbimbing padasaluran ke udara bebas
Masing-masing bentuk antenna punyapola pancaran (radiasi) yang berbeda
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Saluran Transmisi
Agar daya sinyal dapat dipancarkansecara maksimal, maka impedansi outputrangkaian pemancar dengan impedansikarakteristik saluran transmisi, sertaimpedansi beban harus sama (match)
Jika tidak sama, maka akan terjadigelombang pantul
Jika komunikasi radio dipandang dalamkonteks saluran transmisi, maka dapatdigambarkan seperti berikut
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Analogue Signals and Digital
Signals1. Analogue Signals
Analogue signals: These are usually
older electronic gadgets (introduced
before the mid 1990s). A goodexample of an analogue signal is the
loud-speaker of a stereo system.
When the volume is turned up the
sound increases slowly and
constantly.
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Analogue Signals and Digital
Signals2. Digital Signals
Digital signals: Modern electronic
products such as computers and
mobile phones depend on digitalsignals. However, a good example
of a digital signal is Morse Code.
The signal is sent as a series of
on and off pulses. The signal is
either present or it is not.
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Analog signal must be converted into Digitalform (Discrete) before DSP techniques canbe applied. The analog signal is basically
denoted asx
[t] orx
a[t] because it varied bytime. The analog signal comes in form ofsinusoid (sine or cosine wave).
The Analog signal is digitized by usingIntegrated Electronic Circuit device called anAnalog-to-Digital Converter (ADC). Theoutput of ADC will be in the form of binarynumber that represents the analog signal
such as electrical voltage.
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The analog signal are always come with noise.
Thus the noise filtering is needed before the
signal goes to ADC. The filtering can be doneby using DSP techniques.
The special purpose microprocessors are
designed to carry out application of DSP. It is
named as Digital Signal Processors (DSPs)
and used in real time application.
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DSPs are programmable devices and capable of carrying outmillions of instruction per second.
It is vital to know how Digital Signal Processing work before we go
to DSPs (The diagram of the process is shown in Figure 1 and 2).
The signals and systems must come together. The systems areneeded to operate the signals. For example, we need to useThermometer to measure Temperature, Microphone to carry outanalog signal (human voice) and convert it to electrical signal,
Charge-Couple Device (CCD) used in in Camera or Digital Camerato convert image to picture and so on. In general, the system ischaracterized by the type of operation that it performs on thesignal.
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Figure 1 : Digitized process of signal
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Figure 2 : Complete Process of Digital Signal
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From the diagram, it can be seen that ADC and
DAC are 2 vital devices used in signal
processing to convert the signal from analog todiscrete (digital) and vice versa.
ADC is basically consists of Sampler, Quantizer
and Coder. All this elements are built up byCMOS Switched-Capacitor (for Sampling), Op-
Amp (Signal Amplification) & Comparator
(Quantizer).
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Quantization is the conversion of discrete-time continuous-valued to discrete-timediscrete- valued (digital) signal. The
difference of this is called Quantization Error.
The coder in ADC will convert the output ofthe Quantizer to b-bit binary sequence that
can be read by DSPs (Digital SignalProcessors).
The DAC, will perform a reverse operation ofADC in order to generate back analog signal.
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DSP CAN BE APPLIED IN THE FOLLOWING FIELDS :
=> COMMUNICATION SYSTEMS
(MOBILE PHONE, SATELLITE, RADAR, SONAR,INTERNET)
=> ENTERTAINMENT ELECTRONICS
(RADIO, TV, Hi-Fi, CD/VCD/DVD PLAYER,MP3),
=> MULTIMEDIA
(ACOUSTICS, IMAGE, SPEECH RECOGNIZATION&
VIDEO CODING, DIGITAL CAMERA),
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=> MEDICAL INSTRUMENT
(ECG Electrocardiogram provides
information about the condition of patients heart),=> GEOPHYSICS (Seismology)
(Apparatus used to measure earth movement)
=> INSTRUMENTATION(ELECTRONIC TESTER Such as Digital Multimeter,
Oscilloscope)=> IC TECHNOLOGY
=> DATA COMPRESSION
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Advantages of using digital filters
The following list gives some of the mainadvantages of digital over analog filters.
1. A digital filter isprogrammable, i.e. its
operation is determined by a program stored
in the processor's memory. This means thedigital filter can easily be changed without
affecting the circuitry (hardware). An analog
filter can only be changed by redesigning
the filter circuit.
2. Digital filters are easily designed, tested
and implementedon a general-purpose
computer.
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3. The characteristics of analog filter
circuits (particularly those containing
active components) are subject to drift and
are dependent on temperature. Digitalfilters do not suffer from these problems,
and so are extremely stable with respect
both to time and temperature.
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4. Unlike their analog counterparts, digitalfilters can handle low frequencysignals
accurately. As thespeed of DSP technology continues toincrease, digital filters are being applied tohigh frequency
signals in the RF (radio frequency) domain,which in the past was the exclusivepreserve of analog
technology.
5. Digital filters are very much moreversatile in their ability to process signals ina variety of ways; this includes the ability ofsome types of digital filter to adapt tochanges in the characteristics of the signal.
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1. The analog signal are always come with ________2. DSP or digital signal processing is the __________of
the signals digitally or by digital means.
3. ADC is basically consists of_______, Quantizer andCoder.
4. The coder in ADC will _____the output of theQuantizer to b-bit binary sequence that can be read byDSPs (Digital Signal Processors).
5. Unlike their analog counterparts, digital filters canhandle____frequencysignals accurately
Test 1
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NOISEPROCESSING
Sampler
ConvertLow
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Test 1
What is the meaning of DSP ?
List the application of DSP ?
Electrical signal are in two form. What are
they ? List example of digital signals and
analogue signals?
Mention the advantages of using digitalfilters ?
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Deret Fourier
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Menurut Fourier setiap fungsi periodik
dapat dinyatakan sebagai jumlah fungsi
sinus dan cosinus yang tak berhingga
jumlahnya dan dihubungkan secaraharmonis. Maka, karena respons paksaan
terhadap setiap bentuk
sinusoida/cosinusoida dapat ditentukandengan mudah dengan konsep fasor.
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Bentuk Trigonometris dari Deret Fourier
Mula-mula kita tinjau sebuah fungsi periodik f(t) yangdidefinisikan sebagai :
f(t) = f(t + T)
dengan T adalah perioda. Selanjutnya kita anggap bahwafungsi f(t) memenuhi sifat-sifat berikut :
f(t) berharga tunggal dimana, yakni f(t) memenuhi definisimatematis dari sebuah fungsi.
Integral ada (yakni, tidak tak berhingga) untuk
setiap pemilihan to
f(t) mempunyai diskontinuitas yang terbatas banyaknyadidalam setiap perioda
f(t) mempunyai maksimum dan minimum yang terbatasbanyaknya didalam setiap perioda.
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. Dengan adanya fungsi periodik f(t) seperti itu, maka
teorema Fourier mengatakan bahwa f(t) dapat dinyatakan
dengan deret tak berhingga
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GELOMBANG GENAP
GELOMBANG GENAP
f(t) = f(-t)
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GELOMBANG GANJIL
f(t) = - f(-t)
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Contoh :
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Kisi-kisi
Sinyal, deret fourier
Osilator
Power amplifier
Modulasi, demodulasi, sistem rx n tx