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Czy modulacje amplitudy są modulacjami amplitudy? Glosa do prezentacji modulacji liniowych nośnej harmonicznej

Dobrogowski A.

Przegląd Telekomunikacyjny + Wiadomości Telekomunikacyjne

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2017

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nr 12

1184--1188

PL

Powszechne nazywanie modulacji liniowych nośnej sinusoidalnej modulacjami amplitudy nie jest uzasadnione, bowiem modulacji obwiedni zwykle towarzyszy modulacja kąta. Istnieją nawet przypadki, kiedy efektywnie modulowany jest tylko kąt. Rzeczywistą modulacją amplitudy jest wyłącznie modulacja AM. Przyczynami klasyfikacyjnych niedostatków są: historia wynalazków, nie dość konsekwentne interpretowanie pojęcia amplituda i niepostawienie pytania o efekt modulacji amplitudy, która powinna wytwarzać nośną zmodulowaną tylko w amplitudzie. Te dwie ostatnie przyczyny są szczegółowo rozważone w artykule, w którym także zasugerowano pewne zmiany w nazewnictwie. Ponadto w sytuacji specyficznego zakłócenia porównano odbiory homodynowy i heterodynowy. Zaproponowano sekwencję niektórych tematów prezentacji problematyki modulacji liniowych.

EN

Linear modulations of a sinusoidal carrier are usually described as amplitude modulations which is not a proper choice, since an envelope modulation is often accompanied by an angle modulation. There are even some cases, when only the angle is modulated effectively. The actual amplitude modulation is the modulation marked with an acronym AM. The classification and the naming misfits result from three reasons: history of inventions, a lack of a consequent interpretation of the term amplitude and not raising the question on an effect of the amplitude modulation which should produced amplitude only modulated carrier. The last two reasons are considered in the paper in detail. Some naming changes are suggested. Furthermore, for a specific interference the homodyne and the heterodyne receptions are compared. There is a proposal of a sequence of problems explaining concepts of linear modulations.

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The FDM-A AND FAM-C methods with regard to effects associated with transmission of rf signals

Gębura A., Mroszkiewicz K.

Prace Naukowe Instytutu Technicznego Wojsk Lotniczych

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2010

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nr 27

151-164

EN

The paper deals with issues related to analogies between methods used for conditioning, transmission and reception of diagnostic signals with use of the FAM-C1 and FDM-A2 techniques and corresponding phases that happen to phenomena associated with transmission of information in radio engineering. All these cases include modulation, transmission and demodulation of FM signals. The only difference is the content of information transmitted: for the diagnostic signal with use of FAM-C and FDM-A techniques it is the information about technical condition of kinematic pairs within the driving unit (demonstrated by defined modulation to angular velocity of kinematic pairs) whilst broadcast signals are used to transmit speech, music or specific sequences of sounds (acoustic signals). The transmission medium is also different. In case of RF signals conveyed between the transmitter and the receiver it can be air, vacuum or water whilst transmission with use of FAM-C and FDM-A techniques assumes signal propagation via rigid tension members of the transmission unit deployed between the monitored kinematic pairs and the electric current generator. The difference lies also in ranges of the carrier frequency - for broadcast transmission with FM modulation the carrier frequency is from a dozen of MHz to hundreds of MHz whilst FAM-C and FDM-A techniques assume the frequency from dozens of Hz to several kHz. The last major difference is also in the heterodyne3 frequency, which is from a dozen of MHz to hundreds of MHz for the RF transmission and from several hundreds of Hz up to several kHz for diagnostic purposes (depending on how the electric machine is designed).

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Heterodyna odbiornika cyfrowego DRM

Chaciński H., Jaros P.

Biuletyn Wojskowej Akademii Technicznej

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2007

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Vol. 56, nr sp.2

49-55

PL

W pracy przedstawiono układ heterodyny odbiornika DRM (Digital Radio Mundiale) zrealizowany w technologii DDS (direct digital synthesis). W technologii DDS sygnał jest wytwarzany technikami cyfrowymi z próbek sygnału odczytywanego z pamięci. Zrealizowano układ heterodyny, wykorzystując scalony układ DDS typu AD9852 wspomagany mikrokontrolerem AVR. Opracowane i zainstalowane na komputerze PC oprogramowanie umożliwia przyjazne sterowanie pracą układu heterodyny. Oprogramowanie składa się z dwóch części: pierwsza część programu steruje transmisją danych i wizualizacją realizowanych nastaw na ekranie monitora komputerowego; drugą część oprogramowania stanowią procedury w asemblerze mikrokontrolera, odbierające dane konfiguracyjne z komputera PC i dokonujące zmian nastaw w układzie generatora zgodnie z preferencjami użytkownika. Zrealizowany układ generatora pracuje w zakresie częstotliwości od kilkudziesięciu kHz do 90 Mhz.

EN

Receiving DRM (Digital Radio Mundiale) digital radio signals impose different requirements on electrical parameters of single receiver blocks than when receiving analogue modulation signals. An example of significantly higher demand being made is a block of local generator called heterodyne. Direct digital synthesis (DDS) has been used in implementation of a digital receiver's heterodyne system. It consists of fixed-shape wave-forms and frequency stabilization by a reference source, most commonly quartz. Taking into consideration the way in which DDS works, one can say that the signal is not exactly generated, but rather computed by digital systems. The system carrying out the DDS digital frequency synthesis consists of digital phase generator (phase accumulator), function generator, digital/analogue converter, and low-pass filter on the output. Phase accumulator consists of a register and an adder. With each reference generator of the clock, the number stored in the B-bit register is increased by a certain constant N. If the register overflows, carry from the bit is ignored and counting starts over again. Such a situation occurs for every stroke of the clock. Samples read from memory are transmitted to the D/A converter and next the signal is filtered by a low-pass filter. Signal frequency depends on tact frequency, size of phase accumulator register and the number N, being a tunable word. Heterodyne system has been implemented using AD9852 type DDS integrated system by AVR microcontroller-aided. The software developed and installed on a PC enables user-friendly control over heterodyne system functioning. The software consists of two parts: the first part controls data transmission and visualization of implemented settings; the second part consists of procedures in microcontroller's assembler, taking configuration data from PC and making changes to settings of the generator system according to user’s preferences. The implemented generator system operates in the frequency range from tens of kHz to 90 MHz. The required frequency range for the operation of a heterodyne, for the purposes of implemented DRM receiver is significantly smaller: from 45.1 MHz to 75.l MHz. This paper contains the results of a study on the composition of harmonic in the signal being generated and the signal amplitude as a function of retune frequency. Advantages of generators with DDS synthesis are substantial. These are: large frequency resolution and ability to quickly change signal frequency, as well as short setting time. Frequency resolution depends on the size of phase accumulator and the frequency standard. Large resolution is easier to be obtained than in case of the PLL technique. A drawback of direct synthesis is the fact that these systems consume significant amount of power, which results from high switching of generator system's constituents. Stability of the DDS-type generator is very high and depends on stability of the reference generator. The possibility of using very stable atomic standards enables us to use these generators in specialist projects. In the DDS technology, the maximum frequency of signal being generated equals half the frequency of reference signal.