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by disinfoniacs #69 & #1
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Ham radio, that curious pastime of the technical and insane, is a world replete with an array of modes of operation, each one a cipher of the endless possibilities of communication. These modes, with their own esoteric language and technical intricacies, offer an opportunity for the ardent enthusiasts of this obscure art to transmit information across vast distances with remarkable precision.
One of the most widely used of these modes is Frequency Modulation, or FM. FM operates by modulating the frequency of a signal, making it possible to transmit both voice and digital information with an accuracy that borders on the mystical. In fact, FM is so ubiquitous that you may recognize it from the FM broadcast radio band, which employs this mode to bring the news and music that accompany our daily routines.
FM is most commonly found in VHF and UHF voice repeaters and simplex, where its ease of use and clarity have made it a favorite among ham radio operators. However, like a dense fog that can impede even the most skilled navigator, FM can sometimes be hampered by its large bandwidth requirements, which can lead to inefficiencies in certain situations.
Despite its limitations, FM remains a mode of operation that is both versatile and adaptable. In the hands of a skilled operator, it can transmit digital information, as in VHF packet radio transmissions, making it a mode of operation that is constantly evolving and improving.
Let us proceed now to discuss AM and its subordinate, single sideband (SSB), the second most widely used mode in ham radio. Unlike FM, which alters the frequency of a signal to convey information, AM operates by modulating the signal strength, known as amplitude. This explains why it is called amplitude modulation, or AM, for short. Single sideband, on the other hand, is a form of amplitude modulation that uses only one sideband without the carrier for transmitting information.
The graphic above illustrates an AM signal and its two sidebands. Both sidebands are responsible for conveying all the information within the signal, along with the carrier, which resides at the center of the signal. In SSB transmissions, only one of the sidebands (either upper or lower) is used, while the other is suppressed. Lower sideband is used on lower HF bands, while upper sideband is predominantly used for 10-meter HF, VHF and UHF single-sideband communications. SSB is most often utilized for long-distance (weak signal) contacts on the VHF and UHF bands.
SSB transmissions enjoy several benefits over other modes, such as FM. For instance, SSB requires only one sideband, resulting in a more efficient use of bandwidth. While FM signals have a bandwidth of 10-15 kHz, SSB transmissions occupy only 3 kHz. This makes SSB ideal for bandwidth-constrained scenarios or when long-distance communication is necessary. Furthermore, SSB can receive multiple signals simultaneously, whereas FM can only handle one signal at a time.
Let us now turn our attention to the curious case of Morse code, a mode of communication that has long captivated the most astute ham radio enthusiasts. While no longer required for a ham radio license, Morse code remains a popular mode of communication, beloved for its simplicity and reliability. Another name for Morse code is continuous wave, or CW, as it relies on a carrier wave that is switched on and off, creating the distinctive "beeping" sound that has become synonymous with this mode.
Despite its apparent simplicity, Morse code is a remarkably efficient means of communication. It relies on just one on/off tone that can be either long or short, known as "dits" and "dahs" respectively. This straightforward encoding scheme makes it possible to transmit messages with remarkable precision and speed, even under challenging circumstances.
One advantage of Morse code over other modes, such as FM or SSB, is its exceptionally narrow bandwidth. In fact, Morse code has the narrowest bandwidth of any of the common modes, with an approximate maximum bandwidth of just 150 Hz. This narrow bandwidth makes it possible to transmit Morse code signals over long distances using relatively low power, making it a valuable mode of communication for ham radio operators around the world.
Ham radio is not merely limited to voice messages or dits and dahs. One such option, amateur television, represents a fascinating and exciting frontier for the most intrepid ham radio enthusiasts using the NTSC mode to transmit an analog fast-scan color TV signal.
Amateur television represents a major advancement in the field of ham radio, opening up a whole new world of possibilities for those who seek to explore the limits of communication. By combining both voice and video, amateur television makes it possible to convey information with an unparalleled level of clarity and precision, allowing operators to share their experiences with others in real-time. This has made it a favorite among ham radio operators who seek to push the boundaries of what is possible.
As the chart above illustrates, the most efficient mode in terms of bandwidth usage is CW, or Morse code. This venerable mode occupies a mere 150 Hz of bandwidth, making it an ideal choice for low-power, long-distance communication.
Next up is SSB, which requires a narrow bandwidth of just 3 kHz to transmit information. This mode is ideal for long-distance, weak signal communication, and is widely used by ham radio operators around the world.
FM phone signals, which are commonly used for VHF and UHF communication, require a modest bandwidth of 10 to 15 kHz per signal. This is still relatively narrow compared to some other modes, such as amateur television, which utilizes the NTSC fast-scan TV mode and occupies a whopping 6 MHz of bandwidth per transmission.
As this chart illustrates, the amount of bandwidth required to transmit information varies widely depending on the mode being used. While Morse code may be the most efficient mode in terms of bandwidth usage, other modes offer distinct advantages in terms of clarity, speed, and range. The key for any ham radio operator is to carefully consider the requirements of each mode, and to select the optimal mode for a given situation, ensuring effective and reliable communication between stations.
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