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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 beam widthbeamwidth of approximately 3035° -(i.e. 40±17° degreesto 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 beam widthbeamwidth of roughly 3535° degrees.(see Aimingthe antenna spec above), so aiming must be reasonably accurate:

  1. Use a compass bearing to the target node.
  2. Tilt slightly toward the target if it is at a higher or lower elevation.
  3. Use the MeshCore or Meshtastic RSSI/SNR values from the target node to fine-tune aim while rotating the antenna.
  4. Lock the mount when signal is maximised. Mark the final orientation so you can verify it has not shifted after a windstorm.

⚠ 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 (36.5 dBm TX, - −130 dBm sensitivity) with 12 dBi Yagi antennas, 20km20 km apart, flatrun terrain:at the Part 15 limit:

  • TX power: 36.524 dBm (reduced to stay legal with a 12 dBi antenna)
  • TX antenna gain: +12 dBi
  • EIRP: 48.536 dBm (checkthe yourmaximum regionallegal EIRP limits before deploying - FCC limits EIRP for point-to-point at this902–928 power level)MHz)
  • Free space path loss at 20km,20 km, 915 MHz: ~117 dB
  • RX antenna gain: +12 dBi (less RX feedline loss — budget ~1–2 dB for real cable)
  • Received power: 48.536 -− 117 + 12 = - 56.5−69 dBm (before RX feedline loss)
  • RX sensitivity: - −130 dBm
  • Link margin: 73.5~61 dB - more than adequate (free-space figure)

In practice, real-world obstructions and multipath reduce this margin.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;comfortable 73in dB provides very high reliability.practice.

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