LoRa Link Range Optimization

Our STM32F401CCU6 + SX1262 (866 MHz) RC link is holding a solid 400–500 m in open-field line-of-sight, but I need that distance stretched to a dependable 4–5 km before anything else. Latency must eventually settle at ≤ 50 ms, yet the immediate priority is raw, repeatable range.

Current hardware
• Radio: Semtech SX1262 modules
• MCU: STM32F401CCU6
• Antennas: compact leaf on the transmitter, “T” style on the receiver
• Environment: wide, unobstructed fields

What I need from you
• A clear link-budget analysis pinpointing the limiting factors in the present 400–500 m performance
• Concrete antenna and matching network improvements—whether that means retuning the existing leaf/T pair, recommending higher-gain whips, or specifying a small directional option that still suits an RC handset
• Firmware-side optimisation of spreading factor, bandwidth, coding rate, packet timing and duty-cycle so that any range gain does not push latency beyond 50 ms
• Guidance on PCB-level tweaks (grounding, RF trace layout, filtering, shielding) if you find them critical
• A short test plan I can reproduce in the field to confirm the new 4–5 km target

I have full firmware source, schematic and current range-test logs ready to share as soon as we start. Clear, evidence-backed recommendations and concise change sets are valued more than lengthy reports.