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2014-02-03T01:44:21Z

66.167.212.112: /* Definition and first properties */

[[File:SSB bandform.svg|thumb|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 5.002 MHz if upper side band (USB) is used or 4.998 MHz if LSB is used.]]
{{Modulation techniques}}
In [[radio]] communications, '''single-sideband modulation''' ('''SSB''') or '''single-sideband suppressed-carrier''' ('''SSB-SC''') is a refinement of [[amplitude modulation]] that more efficiently uses [[transmitter]] [[electric power|power]] and [[bandwidth (signal processing)|bandwidth]]. Amplitude modulation produces an output signal that has twice the bandwidth of the original [[baseband]] signal. Single-sideband modulation avoids this bandwidth doubling, and the power wasted on a carrier, at the cost of increased device complexity and more difficult tuning at the receiver.

==History==
The first U.S. patent<ref>{{Patent|US|1449382|John Carson/AT&T: "Method and Means for Signaling with High Frequency Waves" filed on December 1, 1915; granted on March 27, 1923}}</ref> for SSB modulation was applied for on December 1, 1915 by [[John Renshaw Carson]]. The U.S. Navy experimented with SSB over its radio circuits before [[World War I]].<ref>[http://dj4br.home.t-link.de/ssb1e.htm The History of Single Sideband Modulation], ''Ing. Peter Weber''</ref><ref>[http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4051940 IEEE, Early History of Single-Sideband Transmission,] ''Oswald, A.A.''</ref> SSB first entered commercial service on January 7, 1927 on the [[longwave]] transatlantic public radiotelephone circuit between New York and London. The high power SSB transmitters were located at [[Rocky Point, New York]] and [[Rugby transmitting station|Rugby, England]]. The receivers were in very quiet locations in [[Houlton, Maine]] and [[Cupar]] Scotland.<ref>[http://massis.lcs.mit.edu/archives/history/underseas.cables History Of Undersea Cables], (1927)</ref>

SSB was also used over [[long distance calling|long distance]] [[telephone line]]s, as part of a technique known as [[frequency-division multiplexing]] (FDM). FDM was pioneered by telephone companies in the 1930s. This enabled many voice channels to be sent down a single physical circuit, for example in [[L-carrier]]. SSB allowed channels to be spaced (usually) just 4,000 [[Hertz|Hz]] apart, while offering a speech bandwidth of nominally 300–3,400 Hz.

[[Amateur radio operator]]s began serious experimentation with SSB after [[World War II]]. The [[Strategic Air Command]] established SSB as the radio standard for its aircraft in 1957.<ref>{{cite web|accessdate=
|format=PDF
|url=http://www.arrl.org/files/file/Technology/pdf/McElroy.pdf
|title=Amateur Radio and the Rise of SSB |publisher=National Association for Amateur Radio}}</ref> It has become a de facto standard for long-distance voice radio transmissions since then.

==Mathematical formulation==

Single-sideband has the mathematical form of [[IQ Modulation|quadrature amplitude modulation]] (QAM) in the special case where one of the [[baseband]] waveforms is derived from the other, instead of being independent messages''':'''

:<math>s_{ssb}(t) = s(t)\cdot \cos(2\pi f_0 t) - \widehat s(t)\cdot \sin(2\pi f_0 t),\,</math>

where <math>s(t)\,</math> is the message, <math>\widehat s(t)\,</math> is its [[Hilbert transform]], and <math>f_0\,</math> is the radio carrier frequency.

Coherent demodulation of <math>s_{ssb}(t)</math> to recover <math>s(t)</math> is the same as AM: multiply by <math>\cos(2\pi f_0 t)</math> and lowpass to remove the "double-frequency" components around frequency <math>2 f_0</math>. If the demodulating carrier is not in the correct phase (cosine phase here), then the demodulated signal will be some linear combination of <math>s(t)</math> and <math>\widehat s(t)</math>, which is usually acceptable in voice communications (if the demodulation carrier frequency is not quite right, the phase will be drifting cyclically, which again is usually acceptable in voice communications if the frequency error is small enough, and amateur radio operators are sometimes tolerant of even larger frequency errors that cause unnatural-sounding pitch shifting effects).

<math>s(t)\,</math> is [[Real number|real-valued]]; therefore its Fourier transform,  <math>S(f),</math>  is [[Hermitian function|Hermitian symmetrical]] about the  <math>f=0</math>  axis.  [[Double sideband]] modulation of <math>s(t)\,</math> to frequency <math>f_0\,</math> moves the axis of symmetry to <math>f=\pm f_0,</math> and the two sides of each axis are called [[sideband]]s. Single-sideband modulation eliminates one sideband of each axis, while preserving <math>s(t).\,</math> 

The easiest way to derive the QAM form above is to consider just the positive-frequency side of <math>S(f).</math>  Its inverse Fourier transform is a complex-valued function, proportional to''':'''

:<math>s_a(t)\ \stackrel{\mathrm{def}}{=}\ s(t)+j\cdot \widehat s(t),\,</math>

which is known as the [[analytic signal|analytic representation]] of <math>s(t).</math>   <math>\widehat s(t)</math>  is real-valued, so  <math>s(t)</math>  is just the real part of its analytic representation.

The product of  <math>s_a(t)\,</math>  with function  <math>e^{j2\pi f_0\cdot t}\,</math>  shifts the one-sided Fourier transform by amount <math>+f_0.</math><ref group="note">See [[Fourier shift theorem|row 103 of the Fourier transform table]]</ref>   The result still has no negative-frequency components, so it is an '''analytic representation''' of the single sideband radio signal''':'''

:<math>s_a(t)\cdot e^{j2\pi f_0 t} = s_{ssb}(t) +j\cdot \widehat s_{ssb}(t).\,</math>

Therefore, with [[Euler's formula]] to expand  <math>e^{j2\pi f_0 t},\,</math>

:<math>
\begin{align}
s_{ssb}(t) &= Re\big\{s_a(t)\cdot e^{j2\pi f_0 t}\big\}\\
&= Re\left\{\ [s(t)+j\cdot \widehat s(t)]\cdot [\cos(2\pi f_0 t)+j\cdot \sin(2\pi f_0 t)]\ \right\}\\
&= s(t)\cdot \cos(2\pi f_0 t) - \widehat s(t)\cdot \sin(2\pi f_0 t).
\end{align}
</math>

The same result can be derived by starting with the model of [[double sideband]] modulation, mathematically remove the lower sideband with an idealized highpass or bandpass filter, and derive the equivalent time-domain form with an inverse Fourier transform.<ref>{{cite web|title=Communication Systems: SSB 1|url=http://thesearemyinterests.blogspot.com/2013/01/communication-systems-ssb-1.html}}</ref><ref>{{cite web|title=Communication Systems: SSB 2|url=http://thesearemyinterests.blogspot.com/2013/01/communication-systems-ssb-2.html}}</ref><ref>{{cite web|title=Communication Systems: SSB 3|url=http://thesearemyinterests.blogspot.com/2013/01/communication-systems-ssb-3.html}}</ref> However, that approach unnecessarily complicates the inverse transform.

===Lower sideband===
<math>s(t)</math>  can also be recovered as the real part of the complex-conjugate, <math>s_a^*(t),</math>  which represents the negative frequency portion of <math>S(f).</math>  When <math>f_0\,</math> is large enough that <math>S(f-f_0)</math> has no negative frequencies, the product  <math>s_a^*(t)\cdot e^{j2\pi f_0 t}</math>  is another analytic signal, whose real part is the actual ''lower-sideband'' transmission''':'''

:<math>s_a^*(t)\cdot e^{j2\pi f_0 t} = s_{lsb}(t) +j\cdot \widehat s_{lsb}(t)\,</math>
:<math>
\begin{align}
s_{lsb}(t) &= Re\big\{s_a^*(t)\cdot e^{j2\pi f_0 t}\big\}\\
&= s(t)\cdot \cos(2\pi f_0 t) + \widehat s(t)\cdot \sin(2\pi f_0 t)
\end{align}
</math>

Note that the sum of the two sideband signals is''':'''

:<math>2s(t)\cdot \cos(2\pi f_0 t),\,</math>

which is the classic model of suppressed-carrier [[double sideband]] AM.

==Practical implementations==
[[File:Collins KWM-1.jpg|thumb|A Collins KWM-1, 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 [[Filter (signal processing)|filter]]ing, 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 [[Amplitude modulation|AM]] 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 [[envelope detector]] like standard AM.

===Hartley modulator===
An alternate method of generation known as a '''Hartley modulator''', named after [[Ralph Hartley|R. V. L. Hartley]], uses [[phase (waves)|phasing]] 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° [[out of phase]] 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<ref>[http://home.earthlink.net/~christrask/pshift.html Earthlink.net], listing numerous articles.</ref> is used. The method was popular in the days of [[vacuum-tube]] radios, but later gained a bad reputation due to poorly adjusted commercial implementations. Modulation using this method is again gaining popularity in the [[Amateur radio homebrew|homebrew]] and [[Digital signal processor|DSP]] fields. This method, utilizing the [[Hilbert transform]] to phase shift the baseband audio, can be done at low cost with digital circuitry.

===Weaver modulator===
Another variation, the '''Weaver modulator''',<ref>"A Third Method of Generation and Detection of Single-Sideband Signals" D K Weaver Jr. Proc. IRE, Dec. 1956</ref> uses only lowpass filters and quadrature mixers, and is a favored method in digital implementations.

In Weaver's method, the band of interest is first translated to be centered at zero, conceptually by modulating a complex exponential <math>\exp(j\omega t)</math> with frequency in the middle of the voiceband, but implemented by a quadrature pair of sine and cosine modulators at that frequency (e.g. 2 kHz). 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===
{{Unreferenced section|date=March 2012}}
In conventional (double sideband) AM the carrier signal is considered to represent a waste of transmission power and therefore SSB transmission generally attempts to reduce the (amplitude) level of the carrier signal to as close as possible to zero. This is known as ''[[suppressed carrier]] SSB''.

However to ensure that the transmitted audio is resolved at the correct pitch it is essential that the receiver is tuned to exactly the same frequency as the transmitter is operating on and it is often difficult to achieve the necessary level of precision. As a result audio transmitted by SSB can sound unnatural (or in severe cases suffer from poor intelligibility), which is why it is considered more suited for speech than music transmission.

To overcome this problem a small amount of carrier signal is transmitted in order that receivers with the necessary circuitry can synchronise with the transmitted signal. This transmission mode is known as ''single sideband [[reduced carrier|reduced (or pilot) carrier]]''.

In other cases it may be desirable to maintain some degree of compatibility with older AM receivers, while still retaining the advantage of reduced transmission bandwidth. This can be accomplished by only reducing the carrier by a small amount (or not at all) this is sometimes referred to as ''compatible (or full carrier) SSB''. Others used the term "Amplitude Modulation Equivalent" (AME). In typical AME devices, the level of quadrature distortion introduced is secondary to conveying the information to a receiver that makes use of an envelope (non-synchronous / phase insensitive) detector rather than the usual product detector utilized for suppressed carrier single sideband. Harmonic distortion with full carrier and one sideband can reach 25%. Intermodulation distortion is significantly higher.

A second, and, perhaps more correct definition of "Compatible Single Sideband" (CSSB) refers to a form of amplitude and phase modulation in which the carrier is transmitted, along with a series of sidebands that are predominantly above or below the carrier term. 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 FM modulation. The signals feeding the phase modulator and the envelope modulator are, further, phase shifted by 90 degrees 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) or most of these higher order terms. In one system, the phase modulated term is actually the log of the value of the carrier level plus the phase shifted audio / information term. 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, 6dB 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 of the formerly unmodulated carrier level. At the point of 100% modulation, the spectrum appears identical to a normal double sideband, AM transmission with the center term (now the primary audio term) at a 0dB reference level and both terms, on each side of the primary sideband at -6dB. The difference is that what appears to be the carrier has shifted by the audio frequency term towards the "sideband in use". 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 20dB at 3 kHz. The result is that the signal does occupy approximately 1/2 the normal bandwidth of a full carrier, DSB signal. 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 if it was ever deployed.

A second series of approaches was designed and patented by [[Leonard R. Kahn]]. 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 1-0.52E term in the denominator of the arcsin generator equation. E represents the envelope term; roughly half the modulation term applied to the envelope modulator is utilized to reduce the second order term of the arcsin "phase" modulated path; thus reducing the second order term in the undesired sideband. A multi-loop modulator / demodulator feedback approach was used to generate an accurate arcsin signal. 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. of NY. 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 cause by this effect is generally quite low and acceptable.

The Kahn CSSB method was also briefly used by [[Airphone]] 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.

While CSSB is seldom used today in the AM/MW broadcast bands worldwide, some experimentation of CSSB continues today in amateur radio allocations.

==Demodulation==
The front end of an SSB receiver is similar to that of an [[Amplitude modulation|AM]] or [[Frequency modulation|FM]] receiver, consisting of a [[superheterodyne]] [[radio frequency|RF]] front end that produces a frequency-shifted version of the radio frequency (RF) signal within a standard [[intermediate frequency]] (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 [[baseband]] frequencies, by using a [[product detector]] which mixes it with the output of a [[beat frequency oscillator]] (BFO). In other words, it is just another stage of heterodyning.(mixing down to base band). For this to work, the BFO frequency must be exactly adjusted.
If the BFO frequency is off, the output signal will be frequency-shifted (up or down), making speech sound strange and "[[Donald Duck]]"-like, or unintelligible.
For audio communications, there is a common agreement about the BFO oscillator shift of 1.7 kHz. A voice signal is sensitive to about 50 Hz shift, with up to 100 Hz still bearable. Some receivers use a [[carrier recovery]] system, which attempts to automatically lock on to the exact IF frequency. The carrier recovery doesn't solve the frequency shift. It gives better S/N ratio on the detector output.

As an example, consider an IF SSB signal centered at frequency <math>F_{if}\,</math> = 45000 Hz. The baseband frequency it needs to be shifted to is <math>F_b\,</math> = 2000 Hz. The BFO output waveform is <math>cos(2\pi\cdot F_{bfo}\cdot t)\,</math>. When the signal is multiplied by (aka '[[heterodyne]]d with') the BFO waveform, it shifts the signal to  <math>(F_{if}+F_{bfo})\,</math>  and to  <math>|F_{if}-F_{bfo}|\,</math>, which is known as the ''beat frequency'' or ''image frequency''. The objective is to choose an <math>F_{bfo}\,</math> that results in  <math>|F_{if}-F_{bfo}|=F_b\,</math> = 2000 Hz. (The unwanted components at <math>(F_{if}+F_{bfo})\,</math> can be removed by a [[lowpass filter]] (for which an output transducer or the human [[ear]] may serve)).

Note that there are two choices for <math>F_{bfo}\,</math>''':''' 43000 Hz and 47000 Hz, called ''low-side'' and ''high-side'' injection. 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 in not inverted, and the non-inverting BFO (43000 Hz) should be used.

If <math>F_{bfo}\,</math> is off by a small amount, then the beat frequency is not exactly <math>F_b\,</math>, which can lead to the speech distortion mentioned earlier.

== SSB as a speech-scrambling technique ==

SSB techniques can also be adapted to frequency-shift and frequency-invert baseband [[waveform]]s.
These effects were used, in conjunction with other filtering techniques, during [[World War II]] as a simple method for speech [[encryption]]. [[Radiotelephone]] [[conversation]]s between the US and [[United Kingdom|Britain]] were intercepted and "decrypted" by the Germans; they included some early conversations between [[Franklin D. Roosevelt]] and [[Winston Churchill|Churchill]]. In fact, the signals could be understood directly by trained operators. Largely to allow secure communications between Roosevelt and Churchill, the [[SIGSALY]] system of digital encryption was devised.

Today, such simple inversion-based speech [[encryption]] techniques are easily decrypted using simple techniques and are no longer regarded as secure.

==Vestigial sideband (VSB)==
[[File:VSB bandform.svg|thumb|VSB modulation]]
A '''vestigial sideband''' (in [[radio]] communication) is a [[sideband]] that has been only partly cut off or suppressed. Television broadcasts (in analog video formats) use this method if the [[video]] is [[transmission (telecommunications)|transmitted]] in [[amplitude modulation|AM]], due to the large [[bandwidth (signal processing)|bandwidth]] used. It may also be used in digital transmission, such as the [[ATSC standard]]ized [[8-VSB]]. The Milgo 4400/48 [[modem]] (circa 1967) used vestigial sideband and [[phase-shift keying]] to provide 4800-bit/s transmission over a 1600 Hz channel.

The video baseband signal used in [[analog TV]] in countries that use [[NTSC]] or [[ATSC]] 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 modulation. In vestigial sideband, the full upper sideband of bandwidth W2 = 4 MHz is transmitted, but only W1 = 1.25 MHz of the lower sideband is transmitted, along with a carrier. 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 [[radio frequency|RF]] and [[intermediate frequency|IF]] filters.

==Frequencies for LSB and USB in amateur radio voice communication==
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 above 10 MHz, upper sideband (USB) is used.<ref>{{cite web|url=http://www.brats-qth.org/training/advanced/operate5.htm |title=BRATS – Advanced Amateur Radio Tuition Course |publisher=Brats-qth.org |date= |accessdate=2013-01-29}}</ref> For example, on the 40m band, voice communications often take place around 7.100 MHz using LSB mode. On the 20m band at 14.200 MHz, USB mode would be used.

== Extended single sideband (eSSB) ==
Extended single sideband is any [[J3E]] (SSB-SC) mode that exceeds the audio bandwidth of standard or traditional 2.9 kHz SSB J3E modes (ITU 2K90J3E) in order to support the fidelity required and desired for relative high fidelity, full range clean and articulate vocal audio.
{| class="wikitable"
|-
! Extended SSB modes !! Bandwidth !! Frequency response !! ITU Designator
|-
| eSSB (Narrow-1a) || 3 kHz || 100 Hz ~ 3.10 kHz || 3K00J3E
|-
| eSSB (Narrow-1b) || 3 kHz || 50 Hz ~ 3.05 kHz || 3K00J3E
|-
| eSSB (Narrow-2) || 3.5 kHz || 50 Hz ~ 3.55 kHz || 3K50J3E
|-
| eSSB (Medium-1) || 4 kHz || 50 Hz ~ 4.05 kHz || 4K00J3E
|-
| eSSB (Medium-2) || 4.5 kHz || 50 Hz ~ 4.55 kHz || 4K50J3E
|-
| eSSB (Wide-1) || 5 kHz || 50 Hz ~ 5.05 kHz || 5K00J3E
|-
| eSSB (Wide-2) || 6 kHz || 50 Hz ~ 6.05 kHz || 6K00J3E
|}

=== ITU designations ===
In 1982, the [[International Telecommunication Union]] (ITU) designated the types of amplitude modulation:
{|class="wikitable"
|-
!Designation!!Description
|-
|A3E||[[double sideband|double-sideband]] full-carrier – the basic amplitude-modulation scheme
|-
|R3E||single-sideband [[Reduced-carrier transmission|reduced-carrier]]
|-
|H3E||single-sideband full-carrier
|-
|J3E||[[Single-sideband suppressed-carrier transmission|single-sideband suppressed-carrier]]
|-
|B8E||[[independent sideband|independent-sideband]] emission
|-
|C3F||[[vestigal sideband|vestigial-sideband]]
|-
|Lincompex||linked [[compander|compressor and expander]]
|}

== Notes ==
{{reflist|group=note}}

==See also==
* [[ACSSB]], amplitude-companded single sideband
* [[Independent sideband]]
* [[Modulation]] for other examples of modulation techniques
* [[Sideband]] for more general information about a sideband

==References==
<references/>

==General references==
*Partly from [[Federal Standard 1037C]] in support of [[MIL-STD-188]]

==Further reading==
* Sgrignoli, G., W. Bretl, R. and Citta. (1995). "VSB modulation used for terrestrial and cable broadcasts." ''IEEE Transactions on Consumer Electronics.'' v. 41, issue 3, p. 367 - 382.
* J. Brittain, (1992). "Scanning the past: Ralph V.L. Hartley", ''Proc. IEEE'', vol.80,p. 463.
* eSSB [http://www.nu9n.com/essb.html]
{{Analogue TV transmitter topics}}

{{DEFAULTSORT:Single-Sideband Modulation}}
[[Category:Radio modulation modes]]
[[Category:Electronic design]]

Talk:Gas constant

2013-12-04T21:41:33Z

66.167.75.42: /* Which calories? */

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If uptime drops below this figure in any given month then you do not pay for that months hosting, it's as basic as that! We would never ever think about utilizing a host that did not provide a solid uptime assurance; this is purely because there is just one good reason a host will not offer an uptime guarantee - undependable uptime! 30 Day cash back assurance - This has actually become a quite standard attribute in the hosting community, though it's nice to have for added peace of mind. Instant setup - A lot of hosting carriers take 24-48 hours to setup your account but Hostgator promises to have you going in under 15 minutes (they do not charge a setup fee either)! Unlimited MySQL data sources - This is very helpful since each Fantastico (see below) script needs its own MySQL database. Fantastico DeLuxe - This excellent program permits you to immediately set up over 50 scripts through your control panel. Scripts include blog sites, online forums, galleries, shopping carts, and more. Endless e-mail accounts - Permits you to have as many, or as couple of, different email addresses as you such as. cPanel control board - At the heart of any hosting experience is the control panel, luckily Hostgator makes use of among the very best systems around, a cPanel. It's well set out and easy to operate. It contains lots of attributes and offers great performance. Most importantly, there is a full working demo on the Hostgator site, so you can test it out yourself! Customer care and technical support Hostgator provides us 24/7 phone support, and live online talk. The reality that you are offered 2 choices to get immediate technical support at any time of the day is excellent. Our experience has actually constantly been very excellent when getting in touch with Hostgator, their operatives are very courteous and most significantly they appear to understand their stuff when dealing with technical problems. Performance The efficiency from Hostgator's servers is outstanding! Hostgator place much tighter limits on the number of internet sites sharing the same server compared with most other shared hosting companies. This provides greater reliability due to the fact that less pressure is put on the servers; and it also significantly improves the speed at which your internet pages run. Server performance is an additional one of the essential locations where Hostgator identify themselves from the group of various other webhosting. Our decision Generally there is so much to like about the method Hostgator does company, they actually do seem to have a good grasp on exactly what the average client needs from an internet hosting supplier. Hardly ever do you stumble upon reports of dissatisfied Hostgator clients, and after hosting with them ourselves we now understand why! Dependability, performance, and uptime from the servers is first rate, likewise customer care is way ahead of the majority of various other web hosts out there. When you loved this informative article and you would want to receive more information about [http://multimisiekpl.cba.pl/?author=4185 Hosgator Reviews] please visit our own web-site. The location where Hostgator really excels is value for cash. At just $9.95 / month for the "Baby" plan (that includes endless domains); anyone planning to host more than one site has a quite easy decision to make. The other terrific thing about this bundle is that you do not have to register to an agreement. You pay on a month-by-month basis, which leaves you cost-free to cancel your account at any time without losing money. To sum up, we do not actually have any bad things about Hostgator; at the costs they charge, we genuinely feel that they offer an exceptional service. Keep up the great Hostgator!