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Docs Radio & RF Design Antenna Design

Antenna Design

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Antenna theory, quarter-wave lengths, antenna types and installation for maximum beacon range

Antenna Design

Overview

The antenna is critical for range performance. The E22-400M30S module includes an SMA connector for easy antenna attachment.

Quarter-Wave Antenna Lengths

FrequencyQuarter-WaveHalf-Wave
433.5 MHz17.3 cm34.6 cm
462 MHz16.2 cm32.4 cm
868 MHz8.6 cm17.3 cm
915 MHz8.2 cm16.4 cm

Tip

The quarter-wave length is calculated as: L = 7155 / f(MHz) cm

Antenna Types

1. Wire Antenna (Simplest)

  • Length: 17.3 cm for 433.5 MHz
  • Material: Solid copper wire, 1-2mm diameter
  • Connection: Solder to ANT pad on E22 module
  • Gain: ~0 dBi
  • Cost: $0.00
  • Type: 433 MHz SMA whip
  • Length: ~17 cm
  • Gain: 2-3 dBi
  • Cost: ~$1-2
  • Source: AliExpress, Amazon

3. SMA Helical Antenna

  • Type: Spring-loaded helical
  • Length: ~10 cm
  • Gain: 1-2 dBi
  • Advantage: Compact, durable
  • Cost: ~$2-3

4. External Antenna (Best Performance)

  • Type: 433 MHz Yagi or omnidirectional
  • Gain: 5-10 dBi
  • Range: 20+ km LOS
  • Use case: Fixed base station

Warning

Never transmit without an antenna connected. This can damage the SX1262 power amplifier.

Installation Tips

Vertical Orientation

Mount the antenna vertically for omni-directional coverage in the horizontal plane. This provides 360-degree coverage for search and rescue operations.

Ground Plane

Adding a ground plane (copper foil or metal plate) beneath the antenna improves gain by approximately 3 dBi. This is especially important for fixed installations.

Keep Away From

  • Battery: Detunes antenna, reduces range
  • Metal enclosure: Blocks signal, causes reflections
  • Human body: Absorbs RF energy at 433 MHz
  • Other antennas: Causes interference

SMA Connector

The E22-400M30S module includes a standard SMA female connector. Use quality SMA cables and connectors to minimize loss.

Note

SMA connectors are rated for 500+ mating cycles. Avoid over-tightening — hand-tight plus 1/4 turn is sufficient.

Weatherproofing

For outdoor installations:

  1. Conformal coating on exposed connections
  2. Heat shrink tubing over solder joints
  3. Silicone sealant around antenna feedthrough
  4. Drip loop in cable to prevent water ingress

Testing

SWR Measurement

Use an SWR meter to verify antenna tuning:

SWRRating
1.0 - 1.5Excellent
1.5 - 2.0Good
2.0 - 3.0Acceptable
> 3.0Poor — retune or replace

Range Test

  1. Set up beacon at known location
  2. Walk away with AM receiver
  3. Note maximum audible distance
  4. Compare with theory (should be 5-15 km LOS)