Understanding Unusual Sounds in Shortwave Radio - A Deep Dive

Many shortwave radio enthusiasts experience a peculiar phenomenon where they hear unusual sounds, often described as hissing or static. Characters like the 'sh' sound you mention are not random but are due to a variety of factors, including natural and artificial noise sources. Let's explore what these sounds really mean and their origins.

Physics Behind Unusual Sounds

The 'sh' sound doesn't come from the shortwave broadcast itself, but rather from the inherent properties of the receiving equipment and the environmental conditions. Here's a detailed look at the scientific basis:

Thermal Noise

The first sound you hear might be 'the sound of The Sun Jacobus Straka and the background radiation of the cosmos,' which is a euphemism for a more common term: 'thunderous noise.' This noise is actually a type of thermal noise, often referred to as 'Johnson noise,' named after John B. Johnson, who described it in 1928. Thermal noise is a random electromagnetic disturbance generated by the inherent thermal motion of charge carriers (electrons and holes) in an electrical conductor. It is a broadband noise that is present in all electrical circuits and can be particularly prominent in the input circuits of amplifiers and receivers.

Shot Noise and Atmospheric Noise

Shot noise is a component of electrical noise that is associated with the discrete nature of electric charge. It is particularly prominent in the first stage of an amplifier. Shot noise can be modulated by various factors, including temperature and varying atmospheric conditions. Atmospheric noise, which is irregular and unpredictable, is a significant contributor to the hissing sound you hear. This noise can be caused by a range of phenomena, from distant lightning storms to the natural movements of the ionosphere.

Noise Sources On Shortwave Frequencies

The unusual sounds on shortwave radio are not limited to the 'sh' noise. Here are some of the common noise sources you might encounter:

Older Receivers and Tubes

Older radio receivers, especially those that use vacuum tubes, can generate a substantial amount of noise. The gas within the tubes and the interaction between the hot filaments and the surrounding atmosphere produce thermal noise. While modern solid-state radios have significantly reduced this issue, they still produce a certain level of internally generated noise.

Lightning and Thunder

Distant and nearby lightning storms can create a steady hissing sound on your radio. Lightning's electrical discharge can interfere with radio signals and generate a distinctive 'crackling' noise. This noise is more noticeable when lightning is closer to the antenna.

Electrical Equipment and Devices

Various household and industrial electrical devices generate noise, often in the form of a 'hum' or 'whine.' Common culprits include refrigerators, air conditioners, fluorescent lights, and other electronic devices. These noises are typically more prominent during their operational cycles and can vary in intensity based on the proximity and functionality of the devices.

Solar Radiation and Space Weather

Perhaps the most intriguing and impactful noise source is the sun. The sun is a primary contributor to the unusual sounds heard, especially on shortwave frequencies. Solar activity, including flares and coronal mass ejections, can produce a significant amount of noise that manifests as a steady hiss. This noise is often referred to as 'solar noise' or 'sun noise.' During periods of high solar activity, you might hear a more pronounced hissing sound as charged particles stream toward Earth and interact with the ionosphere and the radio receivers.

Conclusion

In essence, what you are hearing when you experience unusual sounds on your shortwave radio is not just a product of the radio itself but a complex interplay of various noise sources. From the thermal motion of electrons to distant celestial phenomena, these noises provide a window into the natural and artificial environment around us. Understanding these noise sources can enhance your appreciation of the radio experience and help you sift through the static to uncover more subtle and interesting signals.

Good listening!