MAVLINKHUD

Advanced Modes: F, D, and K

Executive Summary

ELRS is not static. It supports multiple modulation modes tailored for different environments. F-Mode (FLRC) is for pure racing speed. D-Mode (DVDA) is for reliability in noisy environments. K-Mode (Gemini) is the ultimate interference rejection system.

Theory & Concepts

1. FLRC (Fast Long Range Communication)

  • The Physics: FLRC is not LoRa. It is an optimized FSK (Frequency Shift Keying).
  • The Trade: It strips away the heavy error correction of LoRa to achieve ultra-low latency (1ms).
  • The Cost: It has a "Digital Cliff." It doesn't degrade gracefully. You have perfect control, then instant failsafe.
  • Use Case: Drone Racing.

2. DVDA (Deja Vu Diversity Aid)

  • The Logic: Send every packet twice, on two different frequencies.
  • The Math: If the probability of packet loss on Frequency A is 10%, the probability of losing both packets is 1% (10% * 10%).
  • The Result: massive increase in Link Quality (LQ) consistency at the cost of halving the update rate (e.g., 500Hz -> D250).

3. Gemini (K-Mode)

  • The Hardware: Requires dual RF chips (SuperD / Gemini TX).
  • The Operation: It transmits on two frequencies simultaneously.
  • The Benefit: Immunity to narrowband interference. If someone turns on a Wifi router on Channel 1, Channel 2 still gets through.

Architecture (The Engineer's View)

1. The Switch

ELRS switches modes via the Lua script.

  • ArduPilot's Role: ArduPilot is agnostic. It just receives RC packets.
  • However: If you switch to a mode with a different packet rate (e.g., 500Hz -> 50Hz), you must ensure your SRx_ telemetry rates are lowered to match the new bandwidth constraints, or you will buffer-bloat the link.

Key Parameters

  • Packet Rate: Select F1000 for racing, D250 for bando/freestyle, 50Hz for Long Range.

Source Code Reference