Diversity and ESC

Diversity Mode & ESC (Enhanced Signal Clarity)

Diversity reception uses two SCUs (Signal Processing Units) 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

Requirement	Details
Radio	Dual-SCU model: FLEX-8600(M), FLEX-6700(R), FLEX-6600(M), AU-520(M)
Antennas	Two antennas connected to different ports (e.g., ANT1 + ANT2, or ANT1 + RX_A)
License	DIV_ESC feature requires SmartSDR+ or higher
Firmware	v4.x recommended

Single-SCU radios (FLEX-6400, FLEX-6500, AU-510) do not support diversity mode. The DIV button will not appear.

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.

Enabling Diversity

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.

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

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 favor the primary antenna, above 1.0 favors 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 center = gain (center = 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.

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.

Practical Usage

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 minimized
6. Fine-tune the gain slider to optimize 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-polarization antennas are ideal for diversity
• Phase settings are frequency-dependent — what works on 20m may not be optimal on 40m
• ESC state is not saved — you'll need to re-adjust after band changes or reconnects

Protocol Details

For developers and protocol researchers:

Command	Description
slice set <id> diversity=1	Enable diversity (creates child slice)
slice set <id> diversity=0	Disable diversity (removes child slice)
slice set <id> esc=on	Enable ESC beamforming
slice set <id> esc=off	Disable 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)