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Version: 26.10.1

Diversity and ESC

Status

Status: Supported · Applies to: FlexRadio

Diversity reception uses two SCUs to receive the same signal from two different antennas simultaneously. ESC (Enhanced Signal Clarity) combines these signals with adjustable phase and gain to steer nulls toward interference and peaks toward desired signals — real-time antenna beamforming from your shack.

Requirements​

RequirementDetails
RadioA dual-SCU FlexRadio. AetherSDR reads diversity support from the radio model's capabilities (as FlexLib does), so dual-SCU models including the ML, CL, MLS and CLS variants show the DIV button
AntennasTwo antennas connected to different ports (e.g., ANT1 + ANT2, or ANT1 + RX_A)
LicenseDIV_ESC feature requires SmartSDR+ or higher
Firmwarev4.x recommended

Single-SCU radios (for example the FLEX-6400 and FLEX-6500) do not support diversity mode, and the DIV button does not appear. Diversity is a FlexRadio feature; it is not offered on other radio families.

Setup​

  1. Open the VFO widget's Audio tab (speaker icon)
  2. Scroll to the bottom — the DIV button appears alongside the L/R audio pan slider
  3. Click DIV to enable diversity reception

The radio will create a child slice on the second SCU. You'll see a second VFO overlay appear on the panadapter with a different antenna assignment.

Using diversity and ESC​

How diversity works​

When you enable DIV on a slice:

  1. The radio creates a child slice on the second SCU, locked to the parent's frequency
  2. Both SCUs receive the same signal from different antennas
  3. The radio combines both signals into a single audio output on the parent slice
  4. The child slice's independent audio is muted — you hear the combined result on the parent

The child slice appears in AetherSDR with its own VFO overlay (showing a different antenna), but its audio controls are irrelevant while ESC is active — the parent handles everything.

ESC controls​

When DIV is active on a slice, the ESC panel appears below the DIV button in the VFO audio tab. ESC is only shown on the parent slice — the child slice shows DIV but not ESC controls.

ESC Toggle​

Click ESC to enable Enhanced Signal Clarity beamforming. Without ESC enabled, diversity simply combines both antennas with default settings. With ESC, you can steer the combination.

Phase Slider (P)​

The horizontal phase slider adjusts the phase offset between the two antenna signals:

  • Range: 0° to 360° in 5° steps
  • Effect: Rotates the beam pattern — different phase angles will null out interference arriving from different directions
  • Protocol: Sent to the radio as radians (matching SmartSDR)

Gain Slider (G)​

The vertical gain slider adjusts the amplitude balance between antennas:

  • Range: 0.0 to 2.0
  • Default: 1.0 (equal balance)
  • Effect: Values below 1.0 favour the primary antenna, above 1.0 favours the secondary
  • Use case: When one antenna picks up more noise than signal, reduce its contribution

Polar Display​

The circular display shows the current phase and gain as a dot on a polar plot:

  • Angle = phase (0° at top, clockwise)
  • Distance from centre = gain (centre = 0.0, edge = 2.0)
  • Crosshairs mark 0°/90°/180°/270° and the mid-gain reference circle (gain = 1.0)

As you adjust the phase and gain sliders, the dot moves in real time. You can also click anywhere on the polar plot to set phase and gain directly at that point.

ESC Signal Meter​

Below the polar display, a level bar shows signal strength after ESC processing in dBm. This is a real-time readout from the radio's SLC/ESC meter (10 fps). Watch this meter while adjusting phase and gain to find the optimal null or peak:

  • Higher dBm = more signal (or more noise)
  • Lower dBm = deeper null

The goal is usually to find the phase angle where the ESC meter shows the most improvement in SNR — maximum desired signal with minimum interference.

Finding the Best Null​

  1. Enable DIV and ESC
  2. Listen to the signal with interference
  3. Slowly sweep the phase slider from 0° to 360°
  4. Watch the ESC meter — you'll hear interference peak and null as you rotate
  5. Stop at the phase angle where interference is minimised
  6. Fine-tune the gain slider to optimise further

Band Noise Reduction​

Even without a specific interference source, diversity + ESC can reduce overall band noise:

  1. Enable DIV and ESC
  2. Set gain to 1.0 (balanced)
  3. Sweep phase slowly while listening to background noise level
  4. The noise floor will vary with phase — find the minimum

Tips​

  • Different antenna types work best — e.g., a vertical + a horizontal dipole give the most diversity benefit since they respond differently to noise sources
  • Same-band, different-polarisation antennas are ideal for diversity
  • Phase settings are frequency-dependent — what works on 20m may not be optimal on 40m
  • Client noise reduction keeps the two antennas apart. Every AetherSDR noise-reduction method processes left and right separately, so if you pan the two diversity slices to opposite ears, each ear keeps its own antenna (see DSP Noise Mitigation)
  • A diversity child is not a split partner — the SPLIT/SWAP badges ignore it (see Split Operation)
  • ESC state is not saved — you'll need to re-adjust after band changes or reconnects

Reference​

Protocol details​

For developers and protocol researchers:

CommandDescription
slice set <id> diversity=1Enable diversity (creates child slice)
slice set <id> diversity=0Disable diversity (removes child slice)
slice set <id> esc=onEnable ESC beamforming
slice set <id> esc=offDisable ESC beamforming
slice set <id> esc_phase_shift=<radians>Set phase (0 to 2π)
slice set <id> esc_gain=<float>Set gain (0.0 to 2.0)
  • ESC commands are only sent from the diversity parent slice (per FlexLib Slice.cs:3367)
  • SmartSDR uses esc=on/esc=off (not 1/0)
  • Phase is sent in radians, displayed as degrees in the UI
  • Phase steps are 5° (~0.087 radians), matching SmartSDR pcap
  • The radio echoes ESC state in slice status: esc=0 esc_gain=1.000000 esc_phase_shift=0.000000
  • When ESC is enabled, the radio sets the child slice to audio_mute=1 audio_level=0 — the child's audio is absorbed into the parent's ESC processing
  • Feature gated by DIV_ESC license (status: license feature name=DIV_ESC enabled=1 reason=PLUS)

Known issues​

  • With diversity on for two slices on different panadapters, tuning one slice moves the other (#4891).
  • Turning on DIV for a second slice silently breaks up the diversity pair that is already running, with no message (#5352).

Troubleshooting​

The DIV button isn't there​

Your radio model doesn't have dual SCUs, or AetherSDR hasn't detected it yet. The button only appears on dual-SCU models.

  1. Check that your radio is a dual-SCU model (see Requirements).

The ESC controls are missing​

ESC appears only on the parent slice, and only while DIV is on.

  1. Open the Audio tab on the slice where you clicked DIV, not on the child slice.
  2. If DIV is off, click DIV first; the ESC panel appears below it.

My ESC settings were lost​

ESC state is not saved, so it resets after band changes and reconnects.

  1. Re-adjust the phase and gain (see Finding the best null).

See also​