What Is CESSB?
Updated January 1, 2026
Controlled Envelope Single Sideband (CESSB) is a modern improvement to classic SSB modulation. In traditional SSB, speech peaks can trigger clipping, ALC action, or filter “overshoot” artifacts that reduce clarity and waste available talk power. CESSB reshapes and peak-limits the envelope before transmission so your average SSB power rises while keeping the signal clean and contained.
Who Invented CESSB?
CESSB was invented and formally documented by David L. Hershberger, W9GR. The core paper is here (ARRL QEX): https://www.arrl.org/files/file/QEX_Next_Issue/2014/Nov-Dec_2014/Hershberger_QEX_11_14.pdf.
That said, Warren Pratt, NR0V deserves a prominent mention because he has been one of the key people turning “the idea” into practical SDR reality through implementations, tooling, and documentation that operators can actually use. His long-running CESSB resource is here: NR0V’s CESSB page.
NR0V is also the author of the WDSP DSP library, which is widely used across the OpenHPSDR software ecosystem (and many SDR forks). WDSP link: https://github.com/TAPR/OpenHPSDR-wdsp.
Why CESSB Matters for QRP
When running 5–10 watts, every dB counts. A QRP station using CESSB can sound louder and cleaner than a non-CESSB station at the same PEP output. In pileups, contests, or NVIS nets, that efficiency bump can be the difference between being heard or getting buried.
Rigs and Platforms That Implement CESSB
CESSB requires DSP processing and a transmit chain that stays predictable when driven. Some rigs implement it explicitly; others may have “good speech processing,” but not documented CESSB. Here’s an updated overview:
| Radio / Platform | CESSB Support | Notes |
|---|---|---|
| FlexRadio FLEX-6000 series (SmartSDR) | ✔ | SmartSDR speech processor explicitly implements the W9GR CESSB algorithm (PROC: NOR/DX/DX+). CESSB is a core advertised feature for additional talk power. |
| Elecraft K4 / K4D | ✔ | CESSB is explicitly documented and tied to the compression setting; Elecraft notes very large average power increases at high CMP settings (use amplifier caution). |
| Apache Labs ANAN series (with Thetis / PowerSDR mRX) | ✔ | Thetis/OpenHPSDR-based SDR platforms commonly provide CESSB in the TX audio chain; these applications are built around the OpenHPSDR DSP ecosystem and WDSP. |
| OpenHPSDR-compatible SDRs (e.g., Hermes-Lite 2, Radioberry) running Thetis / PowerSDR mRX | ✔ | CESSB availability depends on the SDR software build and TX-chain configuration; common in the OpenHPSDR software family. |
| QRP Labs QMX / QMX+ (SSB firmware) | ✔ | QRP Labs documents a controlled-envelope SSB approach in its SSB firmware context, citing the original W9GR QEX paper. |
| Icom IC-705 / IC-7300 / IC-7610 / IC-9700 | ? | Not confirmed by Icom documentation as “CESSB.” These radios have DSP TX EQ and speech compression, but Icom does not publicly label (or credit) a W9GR-style CESSB feature in the same explicit way as FlexRadio or Elecraft. |
| Yaesu / Kenwood (various modern DSP rigs) | ? | Many offer excellent speech processing and compression, but “CESSB” is not consistently documented as a named feature across models. Treat claims as model/firmware dependent unless the manufacturer/manual explicitly states it. |
How CESSB Works
- Pre-shaping and peak control: Speech is analyzed and peaks are controlled so the transmitted envelope stays within a cleaner, more efficient boundary.
- Lower effective overshoot: By controlling envelope excursions, you reduce the events that trigger harsh limiting, ALC pumping, or unwanted transient artifacts.
- More usable average power: Your PA spends more time near the intended envelope level instead of wasting headroom on brief peaks.
Limitations and Common Misunderstandings
- Not magic: CESSB won’t fix bad mic technique, excessive room noise, or an overly wide TX filter choice.
- “External CESSB” is tricky: You can do envelope/peak processing externally, but whether it behaves like true CESSB depends on the radio’s TX chain (ALC behavior, clipping points, headroom, and filtering). Built-in implementations are usually more predictable.
- Amplifier stress is real: More average power means more heat. If you enable heavy CESSB/compression and then drive an amplifier hard, you may exceed its safe average dissipation even if peak power looks “legal.”
Operating Tips with CESSB
- Set mic gain so peaks are controlled without harsh ALC action. CESSB works best when the chain stays linear.
- Use TX bandwidth wisely (especially for DX/contest). Concentrating energy in the intelligibility range often beats “broadcast wide.”
- If using an amplifier, watch current, temperature, and duty cycle. “More talk power” is still more work for the hardware.
Mini-FAQ
- Who invented CESSB? ... David L. Hershberger, W9GR, in his ARRL QEX paper (linked above).
- What role does NR0V play? ... Warren Pratt (NR0V) helped make CESSB practical in SDR ecosystems via implementations, documentation, and the WDSP DSP library widely used in OpenHPSDR software.
- Which rigs definitely have CESSB? ... FlexRadio FLEX-6000 (SmartSDR) and Elecraft K4/K4D explicitly document W9GR CESSB. OpenHPSDR/Thetis/PowerSDR mRX platforms commonly include it as well.
- Does Icom implement CESSB? ... I can’t confirm “CESSB by name” from Icom documentation. Icom rigs do have DSP speech compression and TX EQ, but they don’t publicly describe it as W9GR CESSB the way FlexRadio and Elecraft do.
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