Building End Fed Half Wave antenna (EFHW) for 40M – 10M

The End Fed Half Wave Antenna (EFHW) 40m – 10m antenna is one of the most popular and versatile multi-band antennas for amateur radio. It requires only a single support, is quick to deploy, and offers excellent performance across the 40m, 20m, 15m, and 10m bands. This design is perfect for operations like POTA (Parks on the Air) or SOTA (Summits on the Air), or simply for hams with limited space.

An EFHW antenna presents a very high impedance (typically$2000-5000) at its feed point. To efficiently match this to your transceiver’s50 ohm output, you need an impedance transformer, commonly a49:1 UNUN (Unbalanced to Unbalanced). This steps down the2500 ohm impedance to approximately50 ohm providing a great match for your coaxial cable.

Overall Dimensions

The complete antenna system measures:

• Total horizontal length: 10.1 meters (33 feet)
• Loading coil position: 1.85 meters (6 feet) from the far end
• Feed point: Through a 1:49 or 1:64 UNUN transformer

End Fed Half Wave Antenna (EFHW)- Key Components

1. Wire Element : The main radiating element consists of standard antenna wire arranged in an inverted-L or horizontal configuration. The total wire length of 10.1 meters is specifically calculated for optimal performance on 40m through 10m bands.

2. Loading Coil (34 uH)

• Inductance: 34 microhenries (uH)
• Construction: 63 turns wound on a 25mm PVC tube
• Position: 1.85m (6 feet) from the far end
• Purpose: Electrically lengthens the antenna for 40-meter operation

The loading coil is a critical component that allows this relatively short antenna to work efficiently on the lower frequency 40-meter band while maintaining performance on higher bands.

3. UNUN Transformer (1:49 or 1:64): The unbalanced-to-unbalanced (UNUN) transformer provides the necessary impedance transformation from the high impedance at the antenna feed point (typically 2000-3000 ohms) down to the standard 50-ohm coaxial cable impedance.The 1:49 or 1:64 UNUN should be housed in a weatherproof enclosure at the feed point. Many commercial UNUNs are available, or you can build your own one.

4. Ground System: The diagram shows an RG-213 coaxial cable connection with a choke balun and connection to the transceiver (TRX). Proper grounding and RF choke implementation are essential for optimal performance.

Building the Loading Coil

To construct the 34 uH loading coil:

1. Obtain a 25mm diameter PVC pipe (approximately 1 inch)
2. Cut a section about 8-10cm long
3. Wind 63 turns of enameled copper wire (18-22 AWG recommended)
4. Space turns evenly for consistent inductance
5. Secure ends with waterproof adhesive or epoxy
6. Weatherproof the completed coil with liquid electrical tape or self-amalgamating tape

 Antenna Wire Configuration

1. Start with approximately 11 meters of antenna wire (allows for adjustment)
2. Install the loading coil at precisely 1.85m from one end
3. Connect the longer section (10.1m side) to the UNUN
4. Attach the feed point end to a suitable support (tree, mast, building)
5. Extend the antenna horizontally or in an inverted-L configuration

EFHW – Performance Characteristics

This  End Fed Half Wave antenna  design provides:

• 40 meters (7 MHz): Full quarter-wave performance with loading coil
• 20 meters (14 MHz): Operates as a half-wave antenna
• 15 meters (21 MHz): Three-quarter wave performance
• 10 meters (28 MHz): Full-wave operation

The multiband capability eliminates the need for an antenna tuner on most bands, though slight adjustments may improve SWR on band edges.

Coax Choke for Isolation

To prevent the coaxial cable shield from becoming part of the radiator and to stop RF from getting back into your station, install acommon-mode choke on the coax. A simple choke can be made fromeight turns of RG58 coax through an FT240-43 toroid, positioned about10-12 feet away from the feed point.

Related Posts

• RA9SUS Simple Loop Antenna covering 14–30 MHz
• Shortened Vertical Antenna for the 80-Meter Band (UR0GT Design)
• 20–40–80 Meter Loaded Multiband HF Dipole Antenna
• Building a Double Bazooka Antenna for HF and VHF Ham Bands
• 9:1 UN-UN Long Wire Transformer for HF Antennas