Directional Antennas
Directional Antennas
Directional antennas concentrate RF energy in a specific direction rather than radiating omnidirectionally. They are used for point-to-point backbone links between fixed sites where maximum range is needed in a known direction.
ALFA 12 dBi Yagi - $50+
A Yagi-Uda directional antenna with 12 dBi gain at 915 MHz. A 12 dBi Yagi has a half-power beamwidth of approximately 35° (i.e. ±17° to the half-power points) and must be aimed precisely at the target node. Used for connecting distant nodes or bridging a gap in mesh coverage across a valley or open terrain. (Pricing as of June 2026; street price varies — confirm against a current retailer listing.)
- Gain: 12 dBi
- Pattern: Directional (Yagi)
- Use case: Point-to-point links, extending mesh over long distances in one direction
When to Use a Directional Antenna
- You need to extend the mesh over a specific long-distance path (e.g., across a lake or through a valley cut)
- You have two sites that need reliable high-margin connectivity but no intermediate repeaters
- You want to add gain without affecting nearby nodes in other directions
When NOT to Use a Directional Antenna
- For a general community repeater that should cover all directions - a Yagi will be deaf and blind to nodes not in its beam
- When nodes are located in multiple directions from the installation point
- On handheld portable devices - you would have to point the device at the target node at all times
Aiming a Yagi
A 12 dBi Yagi has a half-power beamwidth of roughly 35° (see the antenna spec above), so aiming must be reasonably accurate:
- Use a compass bearing to the target node.
- Tilt slightly toward the target if it is at a higher or lower elevation.
- Use the MeshCore or Meshtastic RSSI/SNR values from the target node to fine-tune aim while rotating the antenna.
- Lock the mount when signal is maximised. Mark the final orientation so you can verify it has not shifted after a windstorm.
Link Budget for a Directional Link
⚠ FCC compliance: At 902–928 MHz the conducted output power limit is 1 W (30 dBm) referenced to a 6 dBi antenna. With a 12 dBi antenna (6 dBi above the threshold), 47 CFR § 15.247(b)(4) requires conducted power to be reduced dB-for-dB — down to 24 dBm — capping EIRP at 36 dBm. There is no relaxed point-to-point antenna allowance at 915 MHz (that exception, § 15.247(c)(1), applies only to 2.4 GHz / 5.8 GHz). Running a radio's full output into a 12 dBi Yagi for a 48.5 dBm EIRP link would be roughly 12 dB over the legal limit and is illegal under Part 15. The link budget below uses the compliant 24 dBm / 36 dBm EIRP figures. (The Station G2's higher rated output is intended for other regulatory regimes — e.g. amateur-licensed operation under Part 97 — not US Part 15 unlicensed use.)
Example: Two Station G2 nodes (−130 dBm sensitivity) with 12 dBi Yagi antennas, 20 km apart, run at the Part 15 limit:
- TX power: 24 dBm (reduced to stay legal with a 12 dBi antenna)
- TX antenna gain: +12 dBi
- EIRP: 36 dBm (the maximum legal EIRP at 902–928 MHz)
- Free space path loss at 20 km, 915 MHz: ~117 dB
- RX antenna gain: +12 dBi (less RX feedline loss — budget ~1–2 dB for real cable)
- Received power: 36 − 117 + 12 = −69 dBm (before RX feedline loss)
- RX sensitivity: −130 dBm
- Link margin: ~61 dB - more than adequate (free-space figure)
In practice, real-world obstructions and multipath reduce this margin, and the free-space figure above assumes a clear line of sight that a 20 km link does not get for free. Over 20 km the earth's curvature alone introduces roughly 23 m of path obstruction (≈ d²/17 in metres/km), and the first Fresnel zone radius at midpoint is on the order of 40 m — so a real 20 km link needs substantial combined antenna height (tens of metres) to keep the path clear. Subtract RX feedline loss as well. Treat the large margin as a theoretical ceiling, not a field-achievable number without proper line-of-sight engineering. 20 dB of link margin is considered comfortable in practice.