{"id":780,"date":"2026-06-07T09:35:42","date_gmt":"2026-06-07T07:35:42","guid":{"rendered":"https:\/\/www.i8zse.it\/en\/?page_id=780"},"modified":"2026-06-07T09:46:47","modified_gmt":"2026-06-07T07:46:47","slug":"amplitude-modulation","status":"publish","type":"page","link":"https:\/\/www.i8zse.it\/en\/modulation\/amplitude-modulation\/","title":{"rendered":"Amplitude modulation"},"content":{"rendered":"<p>As is well known, the history of radio begins with one of the simplest forms of long-distance communication: <strong>Morse code<\/strong>.<br \/>\nMorse code can, in many respects, be considered a primitive form of digital transmission, since information is not represented by a continuous quantity but by a discrete sequence of symbols: the dot and the dash, the latter conventionally equivalent to three dots. Transmission therefore occurs through the presence or absence of the carrier, which can be reduced to two logical states, &#8220;on&#8221; (1) and &#8220;off&#8221; (0). Wireless telegraphy thus demonstrated, from its very beginnings, the validity and effectiveness of digital communication, long before the introduction of electronic computers and modern digital signal processing techniques. But let us remain in the <em>analog<\/em> domain.<\/p>\n<p>A fundamental step took place at the beginning of the twentieth century, when <strong>Reginald Fessenden<\/strong> succeeded in transmitting the human voice for the first time using a radio wave as a carrier. This marked the transition from telegraphy to radiotelephony and introduced a completely analog system. It was in this context that <strong>amplitude modulation<\/strong> (AM) was born, in which a high-frequency sinusoidal carrier is varied in amplitude according to the information signal, typically an audio signal.<\/p>\n<p>From an operational standpoint, amplitude modulation consists of <em>shaping<\/em> the envelope of the carrier so that it follows the variations of the modulating signal. This aspect is crucial because it allows for extremely simple demodulation: at the receiver, an envelope detector\u2014often implemented with a diode followed by a filter\u2014is sufficient to recover the audio signal, which can then be amplified and made audible. This circuit simplicity was one of the main reasons for the early success of AM.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-medium wp-image-3121\" src=\"https:\/\/www.i8zse.it\/wp-content\/uploads\/2026\/04\/modulazione-300x277.png\" alt=\"\" width=\"300\" height=\"277\" \/><\/p>\n<p>A fundamental parameter of amplitude modulation is the <em>modulation depth<\/em>, or modulation index, which expresses how much the carrier amplitude is varied by the information signal. When modulation is below 100% (undermodulation), the transmitted signal does not fully exploit its potential, resulting in lower energy efficiency. Conversely, excessive modulation (overmodulation) causes distortion of the envelope, making correct demodulation with simple detectors impossible and generating spurious emissions that extend beyond the intended bandwidth. Proper control of the modulation index is therefore essential to ensure both signal quality and compliance with spectral limits.<\/p>\n<p>When analyzed in the frequency domain, amplitude modulation generates three main components: the carrier and two sidebands, one upper and one lower, symmetrical about the carrier frequency. These sidebands contain the information and are redundant, since they carry the same information content. As a result, the required bandwidth is twice that of the modulating signal: for example, a voice signal limited to approximately 3 kHz requires about 6 kHz of total bandwidth.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-medium wp-image-3122\" src=\"https:\/\/www.i8zse.it\/wp-content\/uploads\/2026\/04\/spettro-300x235.png\" alt=\"\" width=\"300\" height=\"235\" \/><\/p>\n<p>Despite its simplicity, AM has several important limitations. It is particularly sensitive to interference and additive noise, which appear as unwanted amplitude variations and therefore directly degrade the useful signal. Furthermore, its energy efficiency is low: a significant portion of the transmitted power is concentrated in the carrier, which conveys no information, while each sideband contributes only part of the total transmitted power.<\/p>\n<p>To overcome these limitations, several variants were developed over time.<\/p>\n<p>A first evolution was DSB-SC (Double Side Band Suppressed Carrier), in which the carrier is suppressed and only the two sidebands are transmitted, improving efficiency but requiring a more complex receiver capable of reconstructing the carrier. A further refinement is SSB (Single Side Band), in which only one sideband is transmitted, completely eliminating redundant components. This reduces the bandwidth to the minimum necessary (about 3 kHz for voice communications) and concentrates all transmitted power on the information itself, which is why this technique became widely adopted in amateur radio from the middle of the last century onward.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-medium wp-image-3124\" src=\"https:\/\/www.i8zse.it\/wp-content\/uploads\/2026\/04\/AM-300x105.png\" alt=\"\" width=\"300\" height=\"105\" \/> <img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-medium wp-image-3123\" src=\"https:\/\/www.i8zse.it\/wp-content\/uploads\/2026\/04\/dsb-300x105.png\" alt=\"\" width=\"300\" height=\"105\" \/><\/p>\n<p>In amateur radio, SSB has become the reference technique for voice communications on the shortwave bands, thanks to its high spectral and energy efficiency. The choice of which sideband to use follows a long-established convention: LSB (Lower Side Band) is used on the lower HF bands (typically below 10 MHz, such as 160, 80, and 40 meters), while USB (Upper Side Band) is used on the higher bands (starting from 20 meters and above).<\/p>\n<p>This distinction has no inherent physical justification, since both sidebands contain exactly the same information. Rather, it arose from historical and operational standardization considerations, linked to the evolution of radio equipment and the need to ensure compatibility between different stations. The universal adoption of this convention prevents tuning errors and enables interoperability among amateur radio operators worldwide without operational ambiguity.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>As is well known, the history of radio begins with one of the simplest forms of long-distance communication: Morse code. Morse code can, in many respects, be considered a primitive form of digital transmission, since information is not represented by a continuous quantity but by a discrete sequence of symbols: the dot and the dash, [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":771,"menu_order":24,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-780","page","type-page","status-publish","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Amplitude modulation - I8ZSE<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.i8zse.it\/en\/modulation\/amplitude-modulation\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Amplitude modulation - I8ZSE\" \/>\n<meta property=\"og:description\" content=\"As is well known, the history of radio begins with one of the simplest forms of long-distance communication: Morse code. 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