End-Fed Half-Wave Antenna

The end-fed half-wave (EFHW) is a half-wavelength wire fed at one end through a 49:1 impedance transformer (unun). It is the default antenna in SimTX, configured as a 32.5 m wire at 10 m height, which is close to resonance at the default frequency of 4625 kHz.

Try this antenna

This is the original application default. Check SWR rather than assuming the default wire is perfectly matched. When changing bands, adjust the wire deliberately; entering zero keeps the current solver's 32.5 m template.

Compare antenna types and tuning steps · Calculate a starting length · Understand the coverage

Configuration

A single wire hung from the configured height and fed at one end through the 49:1 transformer. Default wire length 32.5 m.

Characteristics

• Typical gain around 2.1 dBi with a takeoff angle around 28 degrees at typical heights.
• Because the end of a half-wave wire presents a very high impedance, the 49:1 transformer is required to bring it near 50 ohms. The transformer costs a small insertion loss (about half a decibel, growing when the match is poor).
• Multi-band behaviour: like all end-fed half-waves it also presents usable matches near integer multiples of its fundamental, with slightly worse match and higher transformer loss on the harmonics.
• Practically convenient: one support, feedpoint at the end.

Sizing

The wire should be an electrical half-wave: roughly 143 to 150 divided by the frequency in MHz, in meters. The default 32.5 m corresponds to a fundamental near 4.6 MHz, which is why the application defaults to 4625 kHz. Operating the default antenna at a very different frequency (for example 7.1 MHz, between its harmonics) produces a severe mismatch and almost no radiated signal; either change the wire length or pick a frequency near a harmonic.

When to use

As a realistic general-purpose wire antenna, especially when simulating portable or space-constrained stations. For best single-band performance a resonant Dipole Antenna at good height still has the edge.