Double Your SSB TX Power with CESSB!

FlexRadio, known for its commitment to innovation, has consistently pushed the boundaries of what’s possible with their transceivers. Among their standout features is CESSB, or Controlled Envelope Single Sideband, introduced by radio pioneer David L. Hershberger, W9GR. In this blog post, we’ll explore the characteristics and benefits of CESSB in SmartSDR for FlexRadio transceivers, while also considering the limitations of standard SSB due to spectrum truncation and nonlinear phase distortion.

David L. Hershberger, W9GR: A Pioneer of CESSB

Before delving into the advantages of CESSB, it’s essential to acknowledge David L. Hershberger, W9GR, as a visionary inventor behind this innovative digital modulation technique. His contributions have significantly influenced amateur radio, enhancing voice communications through innovation.

The Limitations of Standard SSB

Standard Single Sideband (SSB) has been a popular mode for voice communications in amateur radio but has inherent limitations. Two primary challenges associated with standard SSB include spectrum truncation and nonlinear phase distortion due to practical implementation errors in the Hilbert transform.

  1. Spectrum Truncation: Standard SSB often truncates the spectrum during modulation, resulting in the loss of a portion of the voice signal. This compromises audio fidelity, particularly in weak signal conditions and long-distance communication.
  2. Nonlinear Phase Distortion: Standard SSB introduces nonlinear phase distortion during modulation, leading to signal distortion and interference with neighboring frequencies, referred to as “splatter.” This issue is particularly problematic in crowded band conditions, such as contests, and can interfere with weak DX signals on adjacent frequencies.

Benefits of CESSB in FlexRadio

Now, let’s explore the advantages of CESSB and how it addresses the limitations of standard SSB:

  1. Improved Audio Quality: CESSB significantly enhances audio quality through its controlled envelope. Unlike standard SSB, CESSB maintains a constant envelope, reducing distortion and ensuring clear voice signals, even in challenging conditions.
  2. Reduced Interference: CESSB’s clean transmission envelope reduces interference with adjacent channels, making it ideal for crowded band conditions and when operating near weak DX signals.
  3. Extended Range: By improving the signal-to-noise ratio, CESSB enables communication over greater distances, even with lower power levels. This is valuable for DXing and contesting.
  4. Operator Comfort: CESSB eliminates the need for constant manual adjustments to maintain signal quality, allowing operators to focus on communication or contesting without continuous tweaking.
  5. Regulatory Compliance: CESSB’s ability to transmit within cleaner, reduced bandwidths helps FlexRadio operators adhere to regulatory requirements while enjoying high-quality voice communications.
  6. Flexibility: SmartSDR’s CESSB implementation offers users the flexibility to fine-tune processing levels according to their preferences and specific operating conditions. Presets allow quick selection between NORMAL, DX, and DX+ settings, providing different processing characteristics to suit varied needs.



FlexRadio’s pioneering spirit is evident in their innovative implementation of CESSB in their hardware. Their dedication to advancing amateur radio is apparent in their commitment to innovation. FlexRadio has reported a remarkable 2.56 dB increase in average power over fast look-ahead ALC with their CESSB implementation. This power increase could be the difference between being heard when being received close to the noice floor or in the QRM of a contest, but also ensures clear voice transmission, even in crowded band conditions.

Listen and see the clear difference between CESSB enabled or disabled in weak band conditions. The transceiver is a FLEX-6600, but this feature is available in all FLEX-6000 Signature Series transceivers. The demo starts with CESSB enabled, then disabled and enabled again a couple of times. The demo was recorded using a marginal direct path on the 10 meter band. Keep your eyes on the average power bar on the WaveNode meter to the right, you will clearly notice the difference with CESSB enabled vs. disabled (Compressor activity indicated by the meter in lower left part of the screen).

Whether you’re a casual operator seeking improved SSB audio quality or a dedicated contester striving for a competitive edge, CESSB exemplifies the continued evolution of amateur radio technology. It effectively addresses and overcomes the challenges posed by standard SSB. With FlexRadio and CESSB, you’re not just communicating; you’re pushing the boundaries of what’s achievable.

In short, with the FlexRadio 6xxx Signature Series transceiver you are paying for 100 watts but getting the “SSB power” of a close to 200 watts transceiver! 

Dave W9GR Presenting CESSB to the Virtual Ham Expo Audience

For an even deeper understanding of CESSB and its implementation, you can refer to David L. Hershberger, W9GR’s technical reference article available here.

Read more about the FlexRadio 6000 Signature Series here.