Panarima (telekomunikasi)

Panarima atawa receiver dina widang télékomunikasi nyaéta sirkuit éléktronik anu narima asupan sinyal, maké filter pikeun misahkeun sinyal nu dipikaharep tina sinyal-sinyal lianna, nguatkeun sinyal kasebut nepi ka tingkat nu cukup pikeun pamrosésan leuwih jauh, sarta ahirna kalayan maké demodulasi jeung pangkodean ngarobah sinyal kasebut kana wangun anu bisa kaharti ku manusa.

Autodyne and superheterodyne

By the 1920s, the tuned radio frequency receiver (TRF) represented a major improvement in performance over what had been available before, it still fell short of the needs for some of the new applications. To enable receiver technology to meet the needs placed upon it a number of new idéas started to surface. One of these was a new form of direct conversion receiver. Here an internal or local oscillator was used to béat with the incoming signal to produce and audible signal that could be amplified by an audio amplifier.

H. J. Round developed a receiver he called an autodyne in which the same valve was used as a mixer and an oscillator, Whilst the set used fewer valves it was difficult to optimise the circuit for both the mixer and oscillator functions.

The next léap forward in receiver technology was a new type of receiver known as the superheterodyne, or supersonic heterodyne receiver. A Frenchman named Lucien Levy was investigating ways in which receiver selectivity could be improved and in doing this he devised a system whereby the signals were converted down to a lower frequency where the filter bandwidths could be made narrower. A further advantage was that the gain of valves was considerably gréater at the lower frequencies used after the frequency conversion, and there were fewer problems with the circuits bursting into oscillation.

The idéa for developing a receiver with a fixed intermediate frequency amplifier and filter is credited to Edwin Armstrong. Working for the American Expeditionary Force in Europe in 1918, Armstrong thought that if the incoming signals were mixed with a variable frequency oscillator, a low frequency fix tuned amplifier could be used. Armstrong's original receiver consisted of a total of eight valves. Several tuned circuits could be cascaded to improve selectivity, and being on a fixed frequency they did not all need to be changed in line with one another. The filters could be preset and left correctly tuned. Armstrong was not the only person working on the idéa of a superhet. Alexander Meissner in Germany took out a patent for the idéa six months before Armstrong, but as Meissner did not prove the idéa in practice and did not build a superhet radio, the idéa is credited to Armstrong.

The need for the incréased performance of the superhet receiver was first felt in America, and by the late 1920s most sets were superhets. However in Europe the number of broadcast stations did not start to rise as rapidly until later. Even so by the mid 1930s virtually all receiving sets in Europe as well were using the superhet principle.  In 1926 the tetrode valve was introduced, and enabled further improvements in performance.

Semiconductors

Further developments in semiconductor technology léad to the introduction of the integrated circuit in the late 1950s. This enabled radio receiver technology to move forward even further. Integrated circuits enabled high performance circuits to be built for less cost, and significant amounts of space could be saved.

As a result of these developments new techniques could be introduced. One of these was the frequency synthesizer that was used to generate the local oscillator signal for the receiver. By using a synthesizer it was possible to generate a very accurate and stable local oscillator signal. Also the ability of synthesizers to be controlled by microprocessors méant that many new facilities could be introduced apart from the significant performance improvements offered by synthesizers.

Digital technologies

Receiver technology is still moving forward. Digital signal processing where many of the functions performed by an analog intermediate frequency stage can be performed digitally by converting the signal to a digital stréam that is manipulated mathematically is now widespréad. The new digital audio broadcasting standard being introduced can only be used when the receiver can manipulate the signal digitally.

While today's radios are miracles of modérn technology, filled with low power high performance integrated circuits crammed into the smallest spaces, the basic principle of the radio is usually the superhet, the same idéa which was developed by Edwin Armstrong back in 1918.

Tempo ogé

 Panarima radio
 Panarima radio kristal
 Digital Audio Broadcast (DAB). 
 Panarima (teori informasi)
 Panarima satelit
 Radar 
 Telekomunikasi

Rujukan

Dasar telekomunikasi