Antenna Physics · Answered

What Height HF Vertical Antenna Should I Buy?

Electrical length, and the aperture it buys

An antenna doesn't care how many feet of aluminum it is. It cares how many wavelengths it is. The same 24-foot pole is a big antenna on 10 meters, a medium one on 20, and a short one on 80. Electrical length — how much antenna you have in wavelengths — sets how much signal it can capture and launch: its effective aperture, in John Kraus's (W8JK) terms. It explains three things at once:

Short for the band — the antenna still works, but its radiation resistance is small, so the fixed losses in conductors, connectors, and the match take a bigger share of your power. That is every backyard vertical on 80 and 160, and why every foot of height pays most down there.

Near five-eighths of a wave — the current lays the most signal toward the horizon, the low angles where DX lives. The ARRL Antenna Book puts it roughly 3 dB over a quarter-wave. The gain doesn't switch on at one band and off at the next; it builds across several bands on the way up and is strongest near five-eighths.

Too long for the band — past about five-eighths, the pattern splits into a low lobe and a higher one (an extended double Zepp). Still works, still useful — some energy just heads skyward, which is why the core line stops at 28 feet.

One pole covers every band, so on any given day it is short for some, strong on several, and long for others. That is not a compromise. It is what an all-band antenna is — and every Greyline height is one.

Why taller helps on the low bands

On 80 meters a full quarter-wave is about 66 feet. Any residential vertical is shorter than that. Kraus showed that radiation resistance climbs steeply with electrical length, and Zavrel's Antenna Physics frames efficiency as radiation resistance against the losses in series with it. So every added foot on 80 and 160 means less of your power lost before it leaves the yard. Physics, not promise. And on a small lot, any signal on the low bands is a win — operators working 500 to 1,000 miles on 40 through 160 are delighted to be in the game.

Every height, every band — plus bonus bands

We modeled every Greyline height in NEC over average ground, against an ideal quarter-wave standing on a full field of buried radials. Each height runs ahead of that textbook antenna on several bands — with no radials in your yard — while working all the others:

Reading the numbers: the bands not listed aren't weak — they sit close to that full-radial ideal, a little above or a little below, with no radials in your yard. A decibel is about the smallest change an ear can hear. The 28-foot shares the NEC run made at 29 feet. How to read antenna gain → · Every band in the VDA Optimizer →

The limits that decide it

Wind first: every Greyline is ASCE 7-10 rated, flag up and flag down — from 100 / 155 mph at 12 feet to 35 / 55 mph at 28 feet. The flag is the dominant load, so lower it when weather threatens. Then the HOA and the neighbors: a flagpole at 20 feet reads as a flagpole. Then length: whatever you operate, more height is more signal on the low bands, and every height covers the whole dial. Add the 9-foot whip later and the bonus bands move down the dial while everything else stays.

Tell us your lot and what you like to operate, and I will tell you what I would put up. — Jon KL2A · 435-200-4902