The inverted V

What it is

A half-wave dipole hung from a single support at its center, with the two legs sloping down like an upside-down V. It needs one tall mast instead of two, which is why it is such a common first HF antenna.

What the droop changes

Bending the legs downward does three things at once.

• Impedance drops. The legs are closer together and partly cancel each other's fields, so for the same current less power is radiated: the radiation resistance falls from the 73 Ω of a flat dipole. Near a 120° included angle it is typically close to 50 Ω, a convenient match for 50 Ω coax. Sharper angles go lower still.
• The pattern rounds out. Sloping wire radiates some vertically polarized energy, so the deep nulls off the ends of a flat dipole become shallower. Broadside gain is slightly lower.
• The resonant length shifts. Expect to trim the wire a little shorter than the flat-top formula says.

In practice

• Angle. Most are built with an included angle of roughly 90° to 120° or wider. A very steep V gives up performance and brings the ends close to the ground.
• Height. The same rules as a flat dipole apply: the apex height sets the elevation pattern; see Ground effects and height.
• Tune it in place. Cut each leg long, then shorten both equally while watching the SWR. Nearby masts, trees and buildings shift the result.
• Feed. Direct 50 Ω coax works, through a 1:1 balun or common-mode choke at the feed point.
• Support. A non-conductive mast (fiberglass, wood, PVC) stays out of the antenna's way; a metal mast can detune it.

Related

• The half-wave dipoleThe reference antenna: pattern, impedance and length.
• Fan and trap dipolesCovering several bands with one antenna.
• Slopers and the inverted LWire antennas for one support and the low bands.
• Ground effects and heightHow earth and height shape the pattern.
• Baluns and ununsBalanced-unbalanced and impedance transformers.