❤Application of single sideband modulation






❤ Click here: http://eracsocell.fastdownloadcloud.ru/dt?s=YToyOntzOjc6InJlZmVyZXIiO3M6MjE6Imh0dHA6Ly9iaXRiaW4uaXQyX2R0LyI7czozOiJrZXkiO3M6NDE6IkFwcGxpY2F0aW9uIG9mIHNpbmdsZSBzaWRlYmFuZCBtb2R1bGF0aW9uIjt9




































The generation of standard SSB modulation results in large envelope overshoots well above the average envelope level for a sinusoidal tone even when the audio signal is peak-limited. A vestigial sideband in communication is a that has been only partly cut off or suppressed.
However, having one sideband only, it occupies only half the bandwidth. Many airborne applications involving VHF transmissions use air band radio. This spectrum is limited to the band : The spectrum of DSB-SC wave which is obtained by taking the product of x t and c t is shown in fig.
This takes the power of the RF envelope of the transmission and uses the peak level of the note at any instant and it includes any components that may be present. Single sideband power measurement It is often necessary to define the output power of a single sideband transmitter or single sideband transmission. This is due to the transmission of only one sideband component. In the frequency social, it is assumed that the upper sideband is transmitted as it is and the lower sideband is modified into vestigial sideband. Thus the resulting signal has a whose bandwidth is twice the maximum frequency of the original input audio signal. There is no advantage between using either the for or lower sideband. This effectively makes the system AM at low modulation frequencies and SSB at high modulation frequencies. For example it is necessary to know the power application of single sideband modulation a transmitter used for two way radio communication to enable its effectiveness to be judged for glad applications. Strict modulation control must be employed to maintain stability of the system and avoid splatter. The level of the peak envelope power may be stated in Watts, or nowadays figures quoted in dBW or dBm may be used. The first-order sideband has increased in prime until it is now at the same level as the formerly unmodulated carrier. 
Single Sideband, SSB Modulation - The high power SSB transmitters were located at and. However, in order for a receiver to reproduce the transmitted audio without distortion, it must be tuned to exactly the same frequency as the transmitter.
Illustration of the spectrum of AM and SSB signals. The lower side band LSB spectrum is inverted compared to the baseband. As an example, a 2 kHz audio baseband signal modulated onto a 5 MHz carrier will produce a frequency of 5. In communications, single-sideband modulation SSB or single-sideband suppressed-carrier modulation SSB-SC is a type of , used to transmit information, such as an , by. A refinement of , it uses and more efficiently. Amplitude modulation produces an output signal the bandwidth of which is twice the maximum frequency of the original signal. Single-sideband modulation avoids this bandwidth increase, and the power wasted on a carrier, at the cost of increased device complexity and more difficult tuning at the receiver. Radio transmitters work by mixing a RF signal of a specific frequency, the , with the audio signal to be broadcast. In AM transmitters this mixing usually takes place in the final RF amplifier high level modulation. It is less common and much less efficient to do the mixing at low power and then amplify it in a linear amplifier. Either method produces a set of frequencies with a strong signal at the carrier frequency and with weaker signals at frequencies extending above and below the carrier frequency by the maximum frequency of the input signal. Thus the resulting signal has a whose bandwidth is twice the maximum frequency of the original input audio signal. It is not necessary to transmit both sidebands plus the carrier, as a suitable receiver can extract the entire original signal from either the upper or lower sideband. There are several methods for eliminating the carrier and one sideband from the transmitted signal. Producing this single sideband signal is too complicated to be done in the final amplifier stage as with AM. SSB Modulation must be done at a low level and amplified in a linear amplifier where lower efficiency partially offsets the power advantage gained by eliminating the carrier and one sideband. Nevertheless, SSB transmissions use the available amplifier energy considerably more efficiently, providing longer-range transmission for the same power output. In addition, the occupied spectrum is less than half that of a full carrier AM signal. SSB reception requires frequency stability and selectivity well beyond that of inexpensive AM receivers which is why broadcasters have seldom used it. In point to point communications where expensive receivers are in common use already they can successfully be adjusted to receive whichever sideband is being transmitted. Navy experimented with SSB over its radio circuits before. SSB first entered commercial service on January 7, 1927 on the transatlantic public radiotelephone circuit between New York and London. The high power SSB transmitters were located at and. The receivers were in very quiet locations in and Scotland. SSB was also used over , as part of a technique known as FDM. FDM was pioneered by telephone companies in the 1930s. With this technology, many simultaneous voice channels could be transmitted on a single physical circuit, for example in. With SSB, channels could to be spaced usually only 4,000 apart, while offering a speech bandwidth of nominally 300 Hz to 3,400 Hz. The established SSB as the radio standard for its aircraft in 1957. It has become a de facto standard for long-distance voice radio transmissions since then. Frequency-domain depiction of the mathematical steps that convert a baseband function into a single-sideband radio signal. A , an early Amateur Radio transceiver that featured SSB voice capability Bandpass filtering One method of producing an SSB signal is to remove one of the sidebands via , leaving only either the upper sideband USB , the sideband with the higher frequency, or less commonly the lower sideband LSB , the sideband with the lower frequency. Most often, the carrier is reduced or removed entirely suppressed , being referred to in full as single sideband suppressed carrier SSBSC. Assuming both sidebands are symmetric, which is the case for a normal signal, no information is lost in the process. Since the final RF amplification is now concentrated in a single sideband, the effective power output is greater than in normal AM the carrier and redundant sideband account for well over half of the power output of an AM transmitter. Though SSB uses substantially less bandwidth and power, it cannot be demodulated by a simple like standard AM. Hartley modulator An alternate method of generation known as a Hartley modulator, named after , uses to suppress the unwanted sideband. To generate an SSB signal with this method, two versions of the original signal are generated, mutually 90° out of phase for any single frequency within the operating bandwidth. Each one of these signals then modulates carrier waves of one frequency that are also 90° with each other. By either adding or subtracting the resulting signals, a lower or upper sideband signal results. A benefit of this approach is to allow an analytical expression for SSB signals, which can be used to understand effects such as synchronous detection of SSB. Shifting the baseband signal 90° out of phase cannot be done simply by delaying it, as it contains a large range of frequencies. In analog circuits, a wideband 90-degree phase-difference network is used. The method was popular in the days of radios, but later gained a bad reputation due to poorly adjusted commercial implementations. Modulation using this method is again gaining popularity in the and fields. This method, utilizing the to phase shift the baseband audio, can be done at low cost with digital circuitry. Weaver modulator Another variation, the Weaver modulator, uses only lowpass filters and quadrature mixers, and is a favored method in digital implementations. This complex signal or pair of real signals is then lowpass filtered to remove the undesired sideband that is not centered at zero. Then, the single-sideband complex signal centered at zero is upconverted to a real signal, by another pair of quadrature mixers, to the desired center frequency. Full, reduced, and suppressed-carrier SSB This section does not any. Unsourced material may be challenged and. March 2012 Conventional amplitude-modulated signals can be considered wasteful of power and bandwidth because they contain a carrier signal and two identical sidebands. Therefore, SSB transmitters are generally designed to minimize the amplitude of the carrier signal. When the carrier is removed from the transmitted signal, it is called SSB. However, in order for a receiver to reproduce the transmitted audio without distortion, it must be tuned to exactly the same frequency as the transmitter. Since this is difficult to achieve in practice, SSB transmissions can sound unnatural, and if the error in frequency is great enough, it can cause poor intelligibility. In order to correct this, a small amount of the original carrier signal can be transmitted so that receivers with the necessary circuitry to synchronize with the transmitted carrier can correctly demodulate the audio. This mode of transmission is called single-sideband. In other cases, it may be desirable to maintain some degree of compatibility with simple AM receivers, while still reducing the signal's bandwidth. This can be accomplished by transmitting single-sideband with a normal or slightly reduced carrier. This mode is called compatible or full-carrier SSB or amplitude modulation equivalent AME. In typical AME systems, harmonic distortion can reach 25%, and intermodulation distortion can be much higher than normal, but minimizing distortion in receivers with envelope detectors is generally considered less important than allowing them to produce intelligible audio. Since phase modulation is present in the generation of the signal, energy is removed from the carrier term and redistributed into the sideband structure similar to that which occurs in analog frequency modulation. The signals feeding the phase modulator and the envelope modulator are further phase-shifted by 90° with respect to each other. This places the information terms in quadrature with each other; the Hilbert transform of information to be transmitted is utilized to cause constructive addition of one sideband and cancellation of the opposite primary sideband. Since phase modulation is employed, higher-order terms are also generated. Several methods have been employed to reduce the impact amplitude of most of these higher-order terms. This produces an ideal CSSB signal, where at low modulation levels only a first-order term on one side of the carrier is predominant. As the modulation level is increased, the carrier level is reduced while a second-order term increases substantially in amplitude. At the point of 100% envelope modulation, 6 dB of power is removed from the carrier term, and the second-order term is identical in amplitude to carrier term. The first-order sideband has increased in level until it is now at the same level as the formerly unmodulated carrier. At levels below 100% modulation, the sideband structure appears quite asymmetric. When voice is conveyed by a CSSB source of this type, low-frequency components are dominant, while higher-frequency terms are lower by as much as 20 dB at 3 kHz. There is one catch: the audio term utilized to phase-modulate the carrier is generated based on a log function that is biased by the carrier level. At negative 100% modulation, the term is driven to zero 0 , and the modulator becomes undefined. Strict modulation control must be employed to maintain stability of the system and avoid splatter. This system is of Russian origin and was described in the late 1950s. It is uncertain whether it was ever deployed. A second series of approaches was designed and patented by. The various Kahn systems removed the hard limit imposed by the use of the strict log function in the generation of the signal. Earlier Kahn systems utilized various methods to reduce the second-order term through the insertion of a predistortion component. One example of this method was also used to generate one of the Kahn independent-sideband ISB AM stereo signals. It was known as the STR-77 exciter method, having been introduced in 1977. Later, the system was further improved by use of an arcsine-based modulator that included a 1-0. This approach was introduced in 1984 and became known as the STR-84 method. It was sold by Kahn Research Laboratories; later, Kahn Communications, Inc. An additional audio processing device further improved the sideband structure by selectively applying pre-emphasis to the modulating signals. Since the envelope of all the signals described remains an exact copy of the information applied to the modulator, it can be demodulated without distortion by an envelope detector such as a simple diode. In a practical receiver, some distortion may be present, usually at a low level in AM broadcast, always below 5% , due to sharp filtering and nonlinear group delay in the IF filters of the receiver, which act to truncate the compatibility sideband — those terms that are not the result of a linear process of simply envelope modulating the signal as would be the case in full-carrier DSB-AM — and rotation of phase of these compatibility terms such that they no longer cancel the quadrature distortion term caused by a first-order SSB term along with the carrier. The small amount of distortion caused by this effect is generally quite low and acceptable. The Kahn CSSB method was also briefly used by as the modulation method employed for early consumer telephone calls that could be placed from an aircraft to ground. This was quickly supplanted by digital modulation methods to achieve even greater spectral efficiency. The front end of an SSB receiver is similar to that of an or receiver, consisting of a front end that produces a frequency-shifted version of the radio frequency RF signal within a standard IF band. To recover the original signal from the IF SSB signal, the single sideband must be frequency-shifted down to its original range of frequencies, by using a which mixes it with the output of a BFO. In other words, it is just another stage of heterodyning. For this to work, the BFO frequency must be exactly adjusted. For audio communications, there is a common agreement about the BFO oscillator shift of 1. A voice signal is sensitive to about 50 Hz shift, with up to 100 Hz still bearable. Some receivers use a system, which attempts to automatically lock on to the exact IF frequency. The carrier recovery doesn't solve the frequency shift. With high-side injection, the spectral components that were distributed around 45000 Hz will be distributed around 2000 Hz in the reverse order, also known as an inverted spectrum. That is in fact desirable when the IF spectrum is also inverted, because the BFO inversion restores the proper relationships. One reason for that is when the IF spectrum is the output of an inverting stage in the receiver. Another reason is when the SSB signal is actually a lower sideband, instead of an upper sideband. But if both reasons are true, then the IF spectrum is not inverted, and the non-inverting BFO 43000 Hz should be used. SSB techniques can also be adapted to frequency-shift and frequency-invert baseband. This voice scrambling method was made by running the audio of one side band modulated audio sample though its opposite e. These effects were used, in conjunction with other filtering techniques, during as a simple method for speech. Largely to allow secure communications between Roosevelt and Churchill, the system of digital encryption was devised. Today, such simple inversion-based speech techniques are easily decrypted using simple techniques and are no longer regarded as secure. A vestigial sideband in communication is a that has been only partly cut off or suppressed. Television broadcasts in analog video formats use this method if the is in , due to the large used. It may also be used in digital transmission, such as the. The broadcast or transport channel for TV in countries that use or has a bandwidth of 6 MHz. To conserve bandwidth, SSB would be desirable, but the video signal has significant low-frequency content average brightness and has rectangular synchronising pulses. The engineering compromise is vestigial-sideband transmission. This effectively makes the system AM at low modulation frequencies and SSB at high modulation frequencies. The absence of the lower sideband components at high frequencies must be compensated for, and this is done by the and filters. When single-sideband is used in amateur radio voice communications, it is common practice that for frequencies below 10 MHz, lower sideband LSB is used and for frequencies of 10 MHz and above, upper sideband USB is used. For example, on the 40 m band, voice communications often take place around 7. On the 20 m band at 14. An exception to this rule applies to the five discrete amateur channels on the 60-meter band near 5. Extended single sideband is any SSB-SC mode that exceeds the audio bandwidth of standard or traditional 2. Extended SSB modes Bandwidth Frequency response ITU Designator eSSB Narrow-1a 3 kHz 100 Hz ~ 3. It offers improved effective range over standard SSB modulation while simultaneously retaining backwards compatibility with standard SSB radios. ACSSB also offers reduced bandwidth and improved range for a given power level compared with narrow band FM modulation. The generation of standard SSB modulation results in large envelope overshoots well above the average envelope level for a sinusoidal tone even when the audio signal is peak-limited. The standard SSB envelope peaks are due to truncation of the spectrum and nonlinear phase distortion from the approximation errors of the practical implementation of the required Hilbert transform. It was recently shown that suitable overshoot compensation so-called or achieves about 3. This results in an effective average power increase of about 140%. Although the generation of the CESSB signal can be integrated into the SSB modulator, it is feasible to separate the generation of the CESSB signal e. This requires that the standard SSB radio's modulator be linear-phase and have a sufficient bandwidth to pass the CESSB signal. If a standard SSB modulator meets these requirements, then the envelope control by the CESSB process is preserved. National Association for Amateur Radio. Communication System Design Using DSP Algorithms. Hershberger, W9GR, QEX, issue Nov. Hershberger, W9GR, QEX, issue Jan.