SSB - Singe Sideband

SSB, which stands for Single Sideband, is an important type of modulation in amateur radio that has evolved from amplitude modulation (AM). SSB is particularly popular because it allows more efficient use of transmit power and available bandwidth.

 

1. Basic principle

Amplitude modulation (AM) produces two sidebands - the upper sideband (USB) and the lower sideband (LSB) - as well as the carrier signal itself.

SSB is a form of amplitude modulation in which only one of the two sidebands (either USB or LSB) is transmitted, while the other sideband and the carrier are suppressed. This reduces the bandwidth required and increases efficiency.

 

2. Advantages of SSB

  • More efficient use of transmit power: Because SSB concentrates all transmit power in a single sideband, the signal is more efficient and can be transmitted further than AM for the same power.
  • Lower bandwidth: SSB requires about half the bandwidth of AM (typically about 2.5 to 3 kHz), allowing more channels within the available frequency spectrum.
  • Better speech intelligibility: SSB typically provides clearer and more intelligible transmission of speech, which is particularly useful in the lower frequency ranges of shortwave radio.

 

3. Use of USB and LSB

  • There is a convention in amateur radio as to which type of SSB is used in which frequency range:
    • USB (Upper Sideband): Typically used on frequencies above 10 MHz (e.g. 20 metres and above).
    • LSB (Lower Sideband): Used on frequencies below 10 MHz (e.g. in the 40 metre and 80 metre bands).
  • This convention helps to avoid confusion and interference between radio amateurs.

 

4. amateur radio applications

  • Voice communication: SSB is the preferred mode for voice communication on short wave. It is used for both local and worldwide communications.
  • DX communication: Because of its efficiency, SSB is particularly popular for DX contacts, i.e. radio contacts over long distances.
  • Contests: SSB is often used in contests where the aim is to make as many contacts as possible in a given time.

 

5. technical details

  • Filtering: An SSB signal is generated by special filters in a transceiver that allow the desired sideband to pass and suppress the other sideband and the carrier.
  • BFO (Beat Frequency Oscillator): On the receive side of an SSB signal, the suppressed carrier must be added back in order to make the signal intelligible. This is done by the BFO, which is built into the radio's receiver.
  • Fine tuning: When receiving an SSB signal, fine tuning is often required to ensure clear and intelligible speech reproduction.

 

6. Disadvantages

  • More complex technology: The modulation and demodulation of SSB is technically more demanding than AM or FM, which results in higher demands on the radio equipment.
  • Tuning: SSB signals must be tuned very precisely to ensure intelligible transmission. A small deviation in frequency can significantly degrade speech quality.

 

7. History and development

  • SSB was originally developed in the 1930s and 1940s for military and commercial communications. It was adopted by radio amateurs in the 1950s and has since become the standard for voice transmission on short wave.

 

In summary, SSB is a highly efficient and widely used modulation in amateur radio, allowing clear voice communication over long distances while making effective use of the available bandwidth. Despite its technical complexity, the advantages of SSB have given it a central role in amateur radio.