Ssb sc demodulation

There are many users of single sideband modulation. Many users requiring two way radio communication will use single sideband and they range from marine applications, generally HF point to point transmissions, military as well as radio amateurs or radio hams. Single sideband modulation is normally used for voice transmission, but technically it can be used for many other applications where two way radio communication using analogue signals is required.

As a result of its widespread use there are many items of radio communication equipment designed to use single sideband radio including: SSB receiver, SSB transmitter and SSB transceiver equipments. By removing some of the components of the ordinary AM signal it is possible to significantly improve its efficiency. It is possible to see how an AM signal can be improved by looking at the spectrum of the signal. When a steady state carrier is modulated with an audio signal, for example a tone of 1 kHz, then two smaller signals are seen at frequencies 1 kHz above and below the main carrier.

If the steady state tones are replaced with audio like that encountered with speech of music, these comprise many different frequencies and an audio spectrum with frequencies over a band of frequencies is seen. When modulated onto the carrier, these spectra are seen above and below the carrier.

It can be seen that if the top frequency that is modulated onto the carrier is 6 kHz, then the top spectra will extend to 6 kHz above and below the signal. In other words the bandwidth occupied by the AM signal is twice the maximum frequency of the signal that is used to modulated the carrier, i.

Analog Communication - SSBSC Modulation

Amplitude modulation is very inefficient from two points. The first is that it occupies twice the bandwidth of the maximum audio frequency, and the second is that it is inefficient in terms of the power used. The carrier is a steady state signal and in itself carries no information, only providing a reference for the demodulation process.

Single sideband modulation improves the efficiency of the transmission by removing some unnecessary elements.

ssb sc demodulation

In the first instance, the carrier is removed - it can be re-introduced in the receiver, and secondly one sideband is removed - both sidebands are mirror images of one another and the carry the same information. While signals that use single sideband modulation are more efficient for two way radio communication and more effective than ordinary AM, they do require an increased level of complexity in the receiver.

As SSB modulation has the carrier removed, this needs to be re-introduced in the receiver to be able to reconstitute the original audio. This generates a carrier signal that can be mixed with the incoming SSB signal, thereby enabling the required audio to be recovered in the detector. This circuit is often called a product detector because like any RF mixer the output is the product of the two inputs.To demodulate SSB transmissions a beat frequency oscillator or carrier insertion oscillator is used along with a mixer or product detector.

As described in previous pages, single sideband is a form of amplitude modulation where the carrier and one sideband have been suppressed or reduced in level. In order to demodulate single sideband, SSB, it is necessary to reintroduce the carrier. To achieve this two main elements are required:. When receiving SSB it is necessary to have a basic understanding of how a receiver works. Most radio receivers that will be used to receive SSB modulation will be of the superheterodyne type.

Here the incoming signals are converted down to a fixed intermediate frequency. Many radio receivers will have a switch to select this, other receivers will have a BFO pitch control which effectively controls the frequency. The BFO needs to be positioned to be in the correct position for when the signal is in the centre of the receiver passband.

This typically means that it will be on the side of the passband of the receiver. Once this has been done, then the main tuning control of the receiver can be used, and once a signal is audible with the correct pitch, then it is also in the centre of the receiver passband.

Adjust the main tuning control so that the pitch is correct, and the signal should be comprehensible. SSB demodulation basics As described in previous pages, single sideband is a form of amplitude modulation where the carrier and one sideband have been suppressed or reduced in level. Single sideband modulation In order to demodulate single sideband, SSB, it is necessary to reintroduce the carrier. The same type of oscillator was used for SSB demodulation and the term persisted.

It is a more correct term than BFO, but not was widely used. The output from the mixer is the demodulated audio signal. Producing a product or multiplication of the value of the inputs is the function of a mixer, but the term product detector was used in the early days of the use of SSB, and has remained in use, although it is less widely used than it was previously.

With a little practice it should be possible to easily tune in SSB signals. Supplier Directory For everything from distribution to test equipment, components and more, our directory covers it. Selected Video What is a Spectrum Analyzer? Featured articles.The demodulation of single-sideband SSB signals requires special attention, because simple mixing leads to superposition of the upper and lower sidebands at audio frequencies.

The following article gives an overview of the different methods for SSB demodulation and their use in software defined radios.

ssb sc demodulation

SSB modulators and demodulators are sometime also referred to as image reject mixers. The filter method is the traditional SSB reception method in analog superhet receivers. Typically a first mixer translates the signal to an intermediate frequency IF first. At the IF a sharp band-pass filter e.

Then the second mixer converts the remaining sideband to audio frequencies. If required, the audio spectrum can be inverted by using high-side LO injection in one of the mixer stages. The filter method requires the availability of very sharp filters at the IF and is widely spread in the analog domain, where quartz filters are used. Sideband suppression is determined by the sharpness and attenuation of the filter at the unwanted sideband. The phasing method uses complex IQ processing to resolve the superposition of lower and upper sideband at audio frequencies.

The incoming signal is directly converted to audio frequencies by a complex mixer creating I and Q components.

Double-sideband suppressed-carrier transmission

The complex mixer requires a sine and cosine LO e. The following low-pass filters with a width of one sideband determines the final bandwidth. This is hardly practical with analog components. However in the digital domain, the LO phase shift can easily be realized by a sine and cosine waveform. This makes the phasing method interesting for implementation in a software defined radio. In practice already small phase deviations lead to prohibit very good sideband suppression, especially for frequencies at the frequency borders of the sidebands.

ssb sc demodulation

Sideband suppression for the phasing method with different phase and amplitude errors shows the vulnerability to imbalances. Even a tiny amplitude error of only 0. It differs a little bit from the first two methods since it does not resolve any superposition of lower and upper sideband.

Instead the Weaver simply converts a portion of the spectrum to audio frequencies without any ambiguities. The Weaver demodulator uses two complex mixing stages.

The first mixer stages translates the signal in order to center it at zero frequency. A second mixer stage translates the signal in order to align its frequencies with the audio frequencies.

Summing or subtracting I and Q selects the orientation of the output spectrum normal or inverted. The Weaver method is very well suited for software defined radios, because digital mixers and their sine and cosine LO signals can be generated with extremely high phase and amplitude accuracy. The same holds for the two identical low-pass filters.

Thus no gain and phase variations occur and the circuit is perfectly balanced for very high performance. Further methods for SSB demodulation are possible, that e. Therefore its practical relevance is somehow limited. Another method performs signal conversion to the audio band in the frequency domain.

For this purpose first a FFT is executed and then the relevant sideband frequency bins are copied to audio frequencies. SSB Demodulation Techniques The demodulation of single-sideband SSB signals requires special attention, because simple mixing leads to superposition of the upper and lower sidebands at audio frequencies. The filtering method for SSB reception.

ssb sc demodulation

The Phasing method for SSB reception. The Weaver method for SSB reception.Since, the two sidebands carry the same information, there is no need to transmit both sidebands. We can eliminate one sideband.

The process of suppressing one of the sidebands along with the carrier and transmitting a single sideband is called as Single Sideband Suppressed Carrier system or simply SSBSC.

It is plotted as shown in the following figure. In the above figure, the carrier and the lower sideband are suppressed. Hence, the upper sideband is used for transmission. Similarly, we can suppress the carrier and the upper sideband while transmitting the lower sideband. This SSBSC system, which transmits a single sideband has high power, as the power allotted for both the carrier and the other sideband is utilized in transmitting this Single Sideband. Let us consider the same mathematical expressions for the modulating and the carrier signals as we have considered in the earlier chapters.

The quality of the signal gets affected unless the SSB transmitter and receiver have an excellent frequency stability. Previous Page. Next Page. Previous Page Print Page.To demodulate SSB transmissions a beat frequency oscillator or carrier insertion oscillator is used along with a mixer or product detector. As described in previous pages, single sideband is a form of amplitude modulation where the carrier and one sideband have been suppressed or reduced in level.

In order to demodulate single sideband, SSB, it is necessary to reintroduce the carrier. To achieve this two main elements are required:. When receiving SSB it is necessary to have a basic understanding of how a receiver works. Most radio receivers that will be used to receive SSB modulation will be of the superheterodyne type. Here the incoming signals are converted down to a fixed intermediate frequency. Many radio receivers will have a switch to select this, other receivers will have a BFO pitch control which effectively controls the frequency.

The BFO needs to be positioned to be in the correct position for when the signal is in the centre of the receiver passband. This typically means that it will be on the side of the passband of the receiver. Once this has been done, then the main tuning control of the receiver can be used, and once a signal is audible with the correct pitch, then it is also in the centre of the receiver passband.

Adjust the main tuning control so that the pitch is correct, and the signal should be comprehensible. SSB demodulation basics As described in previous pages, single sideband is a form of amplitude modulation where the carrier and one sideband have been suppressed or reduced in level. Single sideband modulation In order to demodulate single sideband, SSB, it is necessary to reintroduce the carrier. The same type of oscillator was used for SSB demodulation and the term persisted.

It is a more correct term than BFO, but not was widely used. The output from the mixer is the demodulated audio signal. Producing a product or multiplication of the value of the inputs is the function of a mixer, but the term product detector was used in the early days of the use of SSB, and has remained in use, although it is less widely used than it was previously. With a little practice it should be possible to easily tune in SSB signals.

Supplier Directory For everything from distribution to test equipment, components and more, our directory covers it. Featured articles.Double-sideband suppressed-carrier transmission DSB-SC is transmission in which frequencies produced by amplitude modulation AM are symmetrically spaced above and below the carrier frequency and the carrier level is reduced to the lowest practical level, ideally being completely suppressed.

DSB-SC transmission is a special case of double-sideband reduced carrier transmission. It is used for radio data systems. This mode is frequently used in Amateur radio voice communications, especially on High-Frequency bands. DSB-SC is generated by a mixer. This consists of a message signal multiplied by a carrier signal.

The mathematical representation of this process is shown below, where the product-to-sum trigonometric identity is used. Demodulation is done by multiplying the DSB-SC signal with the carrier signal just like the modulation process.

This resultant signal is then passed through a low pass filter to produce a scaled version of original message signal. The equation above shows that by multiplying the modulated signal by the carrier signal, the result is a scaled version of the original message signal plus a second term. Once this signal passes through a low pass filter, the higher frequency component is removed, leaving just the original message.

This is best shown graphically. Below is a message signal that one may wish to modulate onto a carrier, consisting of a couple of sinusoidal components with frequencies respectively Hz and Hz. The name "suppressed carrier" comes about because the carrier signal component is suppressed—it does not appear in the output signal.

This is apparent when the spectrum of the output signal is viewed. In the picture shown below we see four peaks, the two peaks below Hz are the lower sideband LSB and the two peaks above Hz are the upper sideband USBbut there is no peak at the Hz mark, which is the frequency of the suppressed carrier. From Wikipedia, the free encyclopedia.

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Coherent Detection of DSB-SC Waves

Federal Standard C. General Services Administration. Archived from the original on Categories : Radio modulation modes. Namespaces Article Talk. Views Read Edit View history. By using this site, you agree to the Terms of Use and Privacy Policy.The carrier does not contain any information and its transmission results in loss of power.

Thus only sidebands are transmitted that contains information. This results in saving of power used in transmission. This saved power can be inserted into the 2 sidebands. Hence, ensuring a stronger signal that transmits over long distances. As during suppression, the baseband signal does not get affected in any way.

As we know that transmission power and bandwidth are the two important parameters in a communication system. Hence, resulting in a considerable power loss.

SSBSC Demodulator

By frequency shifting property of Fourier transform. From the above equation, it is clear that only 2 components are present in the spectrum. The mathematical representation of the signal at the output of the product modulator is given as. Thus, at the output, the DSB-SC wave contains a signal whose frequency is twice the frequency of the baseband signal. The carrier without any information content is suppressed by a balanced modulator.

Its principle of operation is such that, when two signals of the different frequency are passed through a non-linear resistance then an amplitude modulated signal with the suppressed carrier is achieved at the output.

A non-linear device has the capability to produce 2 sidebands with a carrier. On substituting the above-given value of i 1 and i 2 in the output equation, we will have. Thus, from the above expression, it is clear that output voltage is a combination of modulating signal along with the DSB-SC signal. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment.

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