VTX Antenna

🟢 Start — zero knowledge, plain words. 🟡 Hands-on — building or buying, specifics and tradeoffs. 🔴 Specialist — the physics and math behind it.

🟢 Start. The antenna gives shape to the invisible signal. Replace the stock "whips" with proper circular-polarized antennas — the difference in image stability is immediate. Iron rule: never power a VTX without an antenna attached — reflected power can burn out the output stage.

🟡 Hands-on. Linear polarization (dipoles) is simple and light; circular (RHCP/LHCP — "cloverleafs") rejects reflections off the ground and buildings, which wins in FPV. Transmitter and receiver must share the same polarization — RHCP against LHCP loses ~20 dB. Antenna gain (dBi) isn't free energy, it's squashing the radiation "donut": more sideways, less up/down. On the goggles: an omni plus a directional patch in a diversity module. Connectors: SMA vs RP-SMA (the pin differs!), U.FL/MMCX on micro builds.

🔴 Specialist. A dipole's pattern has a null along the antenna's axis — flying directly overhead of a pilot with a vertical antenna means two nulls meeting at once:

   side view (antenna vertical: ¦)

        weak signal (null)
                 ¦
      █████      ¦      █████
      ██████     ¦     ██████     ██ = strong signal
      █████      ¦      █████
                 ¦
        weak signal (null)

Beyond that: axial ratio tells you how "round" a circular polarization really is; the first Fresnel zone with radius $r \approx 8.66\sqrt{d_{\text{km}}/f_{\text{GHz}}}$ m must stay mostly clear (2 km at 5.8 GHz → ~5 m above obstacles); and a carbon plate between antennas can strip a dozen-plus dB off the link — hence antennas on TPU masts.

⚠️ Common mistakes: mixing RHCP with LHCP; powering a VTX with no antenna; servicing at full power with no cooling; camera aspect ratio that doesn't match the goggle setting.

🖼️ Photos: your own antenna comparison (dipole, cloverleaf, patch); "antenna radiation pattern" plots from Wikimedia Commons (many are PD).