What is lsb radio?

A new Technician Class operator is likely to get started in ham radio with VHF and UHF phone operations using FM simplex channels and repeaters. The channelized world of VHF/UHF FM offers relative simplicity of operations and is a great way to get on the air immediately upon earning the Technician Class license. However, after mastering repeaters and gaining comfort with on-air FM phone QSOs, the next step for many hams is the more challenging domain of single sideband (SSB) phone operations.

Single sideband phone ops offer a broader range of radio contact opportunities, including long distance and international communications. Generally, SSB signals tend to propagate greater distances and exhibit more graceful degradation over distance than FM signals. Single sideband phone may be used on the VHF and UHF bands available to the Technician Class licensee, on the 10-meter band phone segment available to Technicians (28.3 to 28.5 MHz), and on all HF phone sub-bands available to higher license classes. Single sideband is the predominant phone mode used for over-the-horizon skip propagation via the ionosphere. This article takes a closer look at the basics of SSB phone mode for better understanding of its complexities and operating nuances relative to FM channelized ops.

Related Learning:

Take a look at our Technician Learning - Section 1.1 media list and listen to the "Mode Characteristics" audio to hear the differences between FM and SSB signals, including signal degradation, noise, and audio quality. In the same section, watch the video "Operations with SSB Mode" to see the operating differences in tuning and signal characteristics with SSB.

What is SSB? Single sideband is a special form of amplitude modulation (AM). What’s so ‘special’ about it? Besides just encoding voice information with variations in signal amplitude, or power, SSB consumes a little less than half the bandwidth of a full “double band” AM signal. Let’s unfold that last statement for the uninitiated new ham.

First, some bandwidth basics: A radio signal is comprised of a range of transmitted frequencies. When an operator tunes up a specific frequency on a transceiver, that displayed frequency value is the carrier frequency. The carrier may be thought of as a reference position for a small, contiguous band of spectrum (frequency range) that will all be transmitted simultaneously when the push-to-talk button is depressed and some voice audio is provided to the microphone. So, a transmitter does not emit only that singular tuned carrier frequency, but rather it emits an entire little band of frequencies near the carrier value that is used to encode the information of all the various audio frequencies of a voice. The extent of this little transmitted band of signals will vary with different types of modulation, or modes, and we refer to the extent or total range of frequencies emitted as the signal’s bandwidth, in units of hertz.

Consider this bar chart comparison of the bandwidth consumed by the signals of common operating modes, including SSB. Notice that FM consumes the widest band of frequencies and is variable from roughly 10 kHz to 15 kHz. (The FM bandwidth varies with the power or ‘loudness’ of the voice audio provided.) Although not a phone mode, CW has the narrowest bandwidth since it must produce only a simple tone and not a wide range of audio frequencies to represent a human voice.

The AM signal is about 6 kHz wide, and if we examine it in more detail we will find that it is actually comprised of two bands, one on each side of the carrier frequency, and they are ‘mirror imaged’ redundant bands or “sidebands.” That is, a complete voice signal is carried by each of the two sidebands comprising the AM signal. Additionally, the AM signal includes transmission of the carrier frequency itself. While this redundant double band AM signal provides robust and high quality audio, it consumes a relatively wide band of spectrum.

As the name implies, single sideband mode utilizes only one of the two AM sidebands and also suppresses the carrier frequency in transmission. So, the SSB signal is just under one-half the bandwidth of the double sideband conventional AM signal. The narrower bandwidth of SSB has a couple of important implications: 1) The SSB signal consumes less of the available spectrum within an amateur band, thereby allowing more signals simultaneously on the band without interference; and 2) The power of a transmission is more densely applied in the narrower band, providing a higher average effective power across the transmitted band, and thereby giving the SSB signal more ‘punch’ than a comparably powered FM or AM signal in which the power is spread across a much broader range of frequencies.

Related Learning:

Take a look at our Technician Learning - Section 1.1 media list and see the video "SSB Bandwidth Advantage" for a visual illustration of the two advantages listed above.

You may now be asking, “Which sideband is used with SSB mode?” The convention used by hams is that bands above the 30-meter band (frequencies higher than 10 MHz), including all VHF and UHF bands, use the upper sideband (USB) – the band of frequencies adjacent to, and higher than, the carrier frequency. For bands below 30-meters (frequencies lower than 10 MHz), the lower sideband is used. [The 30-meter band is a digital modes-only band where SSB is not used, and another exception occurs in the 60-meter band (5.3 MHz) where only five USB channels are allowed.]

The trade-off with SSB as compared to conventional double-sideband AM and especially to FM phone mode is the quality of the audio. Narrower bandwidth dictates a reduction in audio information carried by the SSB signal. As a result, SSB audio will sound a bit thinner and less rich, but it is still quite intelligible and more than sufficient for weak signal phone communications.

Weak Signals: Signals that are transmitted great distances, such as those refracted by the ionosphere over the horizon and back to earth hundreds or thousands of miles distant, become very weak in comparison to the initial output power at the transmitting antenna. As radio waves expand their power is distributed over a greater volume of space, reducing the effective power at a distant receiving station. Further, signal polarization essentially becomes randomized during transit through the ionosphere and earth's magnetic field, further reducing the signal’s ability to induce currents on a distant receiving antenna at which the polarization is unlikely to be matched. These so-called ‘weak signal’ operations benefit from the relatively high power density of the SSB signal noted above.

Even signals that do not utilize ionospheric skip can benefit from the extended reach offered by SSB, such as VHF or UHF signals transmitted across a more local region. It is common for local VHF/UHF SSB signals to be viable well over 100 miles, depending upon specific terrain features and polarization. For non-skip SSB, operators use horizontal polarization with antenna elements parallel to the surface of the earth.

Related Learning:

Take a look at our Technician Learning - Chapter 3 and Chapter 5 lists to learn more about using SSB on VHF and UHF bands in the two articles: "SSB on 2-meters" and "VHF Multi-mode Transceiver."

No SSB Channelization: Unlike FM phone operations, SSB tuning does not use predefined channels. Rather, tuning across a phone sub-band is contiguous. That means that an operator may select any carrier frequency desired across the extent of the sub-band and transmit and receive signals on the 3 kHz bandwidth adjacent to the carrier frequency. The typical receiver will normally employ a SSB receive band of the standard 3 kHz SSB bandwidth, demodulating whatever signals are received within that 3 kHz band into audio. In order to receive a signal properly, the receiver’s receive band must be aligned across the frequencies with the precise band position of the signal being received. Otherwise, if there is misalignment between the receive band position and the signal position, the signal will sound distorted and may be unintelligible. Audio distortion of a received signal is clearly heard as it is gradually ‘tuned in’ to correct registration with the receive band, as you will see and hear in the Technician Learning video "Operations with SSB Mode" recommended near the beginning of this article.

Further, since no predefined channels exist across the band to keep different stations’ signals properly separated from one another as with FM ops, it is easy for signals to ‘overlap’ in the same spectrum space and cause interference. The receiving station will demodulate any and all signals within its receive band of 3 kHz, and sometimes that will be multiple different signals. Some portion of each signal will be heard in the receive audio, with various degrees of distortion and interference to the desired signal. A narrower receive bandwidth may be used by implementing receive filters, helping to reduce any such interference from nearby signals on the band. Receive filters can be implemented to attenuate undesired signals or noise in nearby portions of the band so that the desired signal is more easily demodulated and heard by the operator.

Related Learning:

Take a look at our Technician Learning - Section 6.2 lists to learn more about using receive filters with SSB mode in our article, "SSB Receive Filters."

These are some of the challenges of SSB operations, carefully tuning in a contiguous manner rather than readily snapping through predefined channels, and cleverly implementing various filtering techniques to isolate and select only the single desired signal out of possibly several near the band location in which are operating. It requires a bit more attention to detail to make sure that your signal remains within proper portions of the bands for SSB modes, and that you keep within sub-bands compliant with your license privileges. Good amateur practice also requires that you be considerate on the air, taking care to ensure adequate unused band near your selected carrier frequency before you transmit in order to minimize interference with others. And when interference does occur, be polite and willing to move along to another location on the band for your operations.

-- Stu WØSTU

Lower sideband (LSB)--The common single-sideband operating mode on the 40, 80 and 160-meter amateur bands.

Upper sideband (USB)--The common single-sideband operating mode on the 20, 17, 15, 12 and 10-meter HF amateur bands, and all the VHF and UHF bands.

[Source for both above: http://www.arrl.org/ham-radio-glossary]

It's a historical oddity. Early amateur SSB rigs used a 9 MHz IF system, and it was easier and cheaper to generate LSB below 9 MHz and USB above 9 MHz. With most designs these days, USB and LSB are equally easy to use, but we keep to the old convention.

[Source: http://www.arrl.org/forum/topics/view/1337]

You will notice that on 160, 80 and 40 meters, LSB is mostly used and on the higher frequency bands, USB is used. This is a leftover from the early days of SSB when radios were designed a certain way, when SSB was in its infancy. Operating habits will not likely change in the future.

[Source: http://www.arrl.org/forum/topics/view/190]

Single Sideband (SSB)

Whereas an AM transmitter outputs two identical copies of the voice information, called sidebands, a SSB signal outputs only one. This signal is much more efficient and saves precious radio-spectrum space. (AM still has a dedicated following of hams who appreciate the mode’s characteristic fidelity and equipment, however.)

Most voice signals on HF are SSB, so you have to choose between USB upper sideband (USB) and lower sideband (LSB). The actual SSB signals extend in a narrow band above (USB) or below (LSB) the carrier frequency displayed on the radio.

How do you choose? By long tradition stemming from the design of the early sideband rigs, on the HF bands above 9 MHz, the convention is that voice operation takes place using USB. Below 9 MHz, you find everyone on LSB except (by FCC decree) on 60 meters.

Because hams must keep all signals within the allocated bands, you need to remember where your signal is actually transmitted. Most voice signals occupy about 3 kHz of bandwidth. If the radio is set to USB, your signal appears on the air starting at the displayed frequency up to 3 kHz higher.

Similarly, on LSB, the signal appears up to 3 kHz below the displayed frequency. When you’re operating close to the band edges, make sure that your signal stays in the allocated band. On 20 meters, for example, the highest frequency allowed for ham signals is 14.350 MHz.

When transmitting a USB signal, you may tune your radio no higher than 14.350 MHz — 3 kHz = 14.347 MHz to keep all your signal inside the band and stay legal.

In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, that are the result of the modulation process. The sidebands carry the information transmitted by the radio signal. The sidebands comprise all the spectral components of the modulated signal except the carrier. The signal components above the carrier frequency constitute the upper sideband (USB), and those below the carrier frequency constitute the lower sideband (LSB). All forms of modulation produce sidebands.

We can illustrate the creation of sidebands with one trigonometric identity:

Adding cos ⁡ ( A ) {\displaystyle \cos(A)} to both sides:

Substituting (for instance)   A ≜ 1000 ⋅ t {\displaystyle A\triangleq 1000\cdot t}   and   B ≜ 100 ⋅ t , {\displaystyle B\triangleq 100\cdot t,}   where t {\displaystyle t} represents time:

Adding more complexity and time-variation to the amplitude modulation also adds it to the sidebands, causing them to widen in bandwidth and change with time. In effect, the sidebands "carry" the information content of the signal.[1]

In the example above, a cross-correlation of the modulated signal with a pure sinusoid, cos ⁡ ( ω t ) , {\displaystyle \cos(\omega t),} is zero at all values of ω {\displaystyle \omega } except 1100, 1000, and 900. And the non-zero values reflect the relative strengths of the three components. A graph of that concept, called a Fourier transform (or spectrum), is the customary way of visualizing sidebands and defining their parameters.

Amplitude modulation of a carrier signal normally results in two mirror-image sidebands. The signal components above the carrier frequency constitute the upper sideband (USB), and those below the carrier frequency constitute the lower sideband (LSB). For example, if a 900 kHz carrier is amplitude modulated by a 1 kHz audio signal, there will be components at 899 kHz and 901 kHz as well as 900 kHz in the generated radio frequency spectrum; so an audio bandwidth of (say) 7 kHz will require a radio spectrum bandwidth of 14 kHz. In conventional AM transmission, as used by broadcast band AM stations, the original audio signal can be recovered ("detected") by either synchronous detector circuits or by simple envelope detectors because the carrier and both sidebands are present. This is sometimes called double sideband amplitude modulation (DSB-AM), but not all variants of DSB are compatible with envelope detectors.

In some forms of AM, the carrier may be reduced, to save power. The term DSB reduced-carrier normally implies enough carrier remains in the transmission to enable a receiver circuit to regenerate a strong carrier or at least synchronise a phase-locked loop but there are forms where the carrier is removed completely, producing double sideband with suppressed carrier (DSB-SC). Suppressed carrier systems require more sophisticated circuits in the receiver and some other method of deducing the original carrier frequency. An example is the stereophonic difference (L-R) information transmitted in stereo FM broadcasting on a 38 kHz subcarrier where a low-power signal at half the 38-kHz carrier frequency is inserted between the monaural signal frequencies (up to 15 kHz) and the bottom of the stereo information sub-carrier (down to 38–15 kHz, i.e. 23 kHz). The receiver locally regenerates the subcarrier by doubling a special 19 kHz pilot tone. In another example, the quadrature modulation used historically for chroma information in PAL television broadcasts, the synchronising signal is a short burst of a few cycles of carrier during the "back porch" part of each scan line when no image is transmitted. But in other DSB-SC systems, the carrier may be regenerated directly from the sidebands by a Costas loop or squaring loop. This is common in digital transmission systems such as BPSK where the signal is continually present.

If part of one sideband and all of the other remain, it is called vestigial sideband, used mostly with television broadcasting, which would otherwise take up an unacceptable amount of bandwidth. Transmission in which only one sideband is transmitted is called single-sideband modulation or SSB. SSB is the predominant voice mode on shortwave radio other than shortwave broadcasting. Since the sidebands are mirror images, which sideband is used is a matter of convention.

In SSB, the carrier is suppressed, significantly reducing the electrical power (by up to 12 dB) without affecting the information in the sideband. This makes for more efficient use of transmitter power and RF bandwidth, but a beat frequency oscillator must be used at the receiver to reconstitute the carrier. If the reconstituted carrier frequency is wrong then the output of the receiver will have the wrong frequencies, but for speech small frequency errors are no problem for intelligibility. Another way to look at an SSB receiver is as an RF-to-audio frequency transposer: in USB mode, the dial frequency is subtracted from each radio frequency component to produce a corresponding audio component, while in LSB mode each incoming radio frequency component is subtracted from the dial frequency.

Frequency modulation also generates sidebands, the bandwidth consumed depending on the modulation index - often requiring significantly more bandwidth than DSB. Bessel functions can be used to calculate the bandwidth requirements of FM transmissions. Carson's rule is a useful approximation of bandwidth in several applications.

Sidebands can interfere with adjacent channels. The part of the sideband that would overlap the neighboring channel must be suppressed by filters, before or after modulation (often both). In broadcast band frequency modulation (FM), subcarriers above 75 kHz are limited to a small percentage of modulation and are prohibited above 99 kHz altogether to protect the ±75 kHz normal deviation and ±100 kHz channel boundaries. Amateur radio and public service FM transmitters generally utilize ±5 kHz deviation.

To accurately reproduce the modulating waveform, the entire signal processing path of the system of transmitter, propagation path, and receiver must have enough bandwidth so that enough of the sidebands can be used to recreate the modulated signal to the desired degree of accuracy.

In a non-linear system such as an amplifier, sidebands of the original signal frequency components may be generated due to distortion. This is generally minimized but may be intentionally done for the fuzzbox musical effect.

LSB also stands for Lower Side Band, which is a term denoting the sideband produced by the difference frequencies when one signal is modulated by another as in FM synthesis or broadcast transmissions. The result of one signal or waveform being modulated by another (or others).