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Introduction
Amateur radio enthusiasts are likely familiar with Single Side Band (SSB), a popular mode of voice transmission. However, SSB hasn't always been the standard. In the early days of radio, Amplitude Modulation (AM) was the widely used form of voice transmission. This blog explores the progression from AM to SSB, how SSB was developed, and its advantages and applications in weak signal conditions.
The Era of Amplitude Modulation (AM)
Before the introduction of SSB, AM was the primary mode of voice transmission on radio waves. AM was simple to receive, even with basic equipment like a crystal set and headphones. It was popular because it not only transmitted voice effectively, but also music. AM signals are still widely used today on medium and longwave bands.
The Need for Single Side Band (SSB)
So why did the need for SSB arise if AM was already popular? The main reason is that SSB occupies less space, allowing for more channels. Additionally, SSB performs exceptionally well in weak signal conditions, making it ideal for communication in noisy environments. However, SSB is not suitable for transmitting music, which is why AM still continues to be used today.
The Complexity of AM Transmitters
While receiving AM signals is straightforward, transmitting them is more complex and inefficient. AM transmitters consist of a carrier signal that is constantly transmitted, along with modulation applied to increase the transmitter's power in sync with the audio input. This constant power transmission requires well-rated components and results in inefficiency. High-level modulation, where modulation is applied to the output stages of the transmitter, is a popular method, but it demands high audio levels and complex components.
The Development of SSB
To understand how SSB was developed, it's essential to visualize an AM transmission. A typical AM transmission consists of two sidebands and a carrier frequency. SSB was developed by removing the carrier signal and one of the sidebands, resulting in a narrower transmission channel. This process, known as "nulling out the carrier," significantly improves efficiency and allows for better signal-to-noise ratio in weak signal conditions.
Transition to SSB Transmitters
The introduction of commercial SSB transmitters for handbands began in the early 1950s, but SSB didn't become popular until the 1960s. Many amateur radio operators were still using AM until the late 1950s. In the early days of SSB, equipment was often homebuilt, and crystals were commonly used to create narrow passbands. Phasing was another alternative system, although it was challenging for home builders to construct and maintain. The first British SSB transmitter was the KW Viceroy, available in both low and high power versions.
The Advantages of SSB
SSB offers several advantages over AM, making it the preferred mode for many amateur radio operators. The narrow transmission channel width (usually around 2.8 kHz) allows for more channels and better signal-to-noise ratio. SSB transmitters are more efficient because they only generate power when audio is present. Tuning in SSB signals is relatively simple, and modern receivers are designed to receive SSB without the need for a separate BFO (Beat Frequency Oscillator).
SSB Tuning and Frequencies
Tuning in SSB signals may require some practice for beginners. In the LSB (Lower Side Band) mode, tuning from high to low frequencies in each band is often easier. On the other hand, tuning in USB (Upper Side Band) mode is more straightforward when starting from the bottom of the band and tuning up. It's important to note that SSB is not channelized, unlike other modes like FM. Operators should be prepared to adjust frequencies within the band and not expect all SSB signals to be on specific channels.
SSB for Weak Signal Communication
SSB is highly effective for weak signal communication, and many operators choose to operate using QRP (low power) levels. QRP, officially defined as 5 watts and below, can still provide significant coverage in SSB. While power levels have increased over the years, SSB remains a reliable mode for weak signal communication. It's worth noting that with the rise in power levels, competition among SSB operators has also increased.
Conclusion
SSB has come a long way since its introduction in the early 20th century. As technology advanced, the amateur radio community embraced SSB for its efficiency and effectiveness in weak signal conditions. Although AM is still used today, SSB has become the standard mode for voice transmission in amateur radio. Whether you're a newcomer or an experienced operator, SSB continues to provide reliable communication and opens up a world of possibilities for amateur radio enthusiasts.
