Greyline VDA Optimizer - Antenna Gain & Wind Calculator
Greyline VDA Optimizer
Pick a Greyline configuration. See the modeled gain on every band, the ASCE 7-10 wind rating, and how your VDA compares with an ideal quarter-wave vertical on a full field of buried radials — the antenna most lots can't hold. Every height works every band. Two modes: explore freely in the playground, or tell us your height limit and we'll find the most antenna your lot can hold.
What the numbers mean
VDA Peak Gain (dBi) — how strong your signal is at the antenna's best elevation angle, compared to a theoretical isotropic radiator. NEC-modeled values for 40m through 10m.
1/4 Wave Reference — the textbook baseline: a quarter-wave vertical standing on a full field of buried radials, about 0 dBi at its best. It is the antenna in the books — and the one almost no small lot can build. Most backyard quarter-waves with a handful of radials never reach it (Severns, N6LF).
VDA vs Quarter-Wave — how your Greyline compares with that ideal, with no radials in your yard. A plus means you are ahead of it. A zero means you match it. A small minus — −0.1, −0.5, even −1 — means within a decibel of it, which no ear on the other end will hear. About 1 dB is barely audible; 3 dB doubles your power; about 6 dB is one S-unit. Do not be afraid of these numbers. How to read antenna gain →
Low bands — on 40, 60, 80, and 160, every backyard vertical is electrically short, and height is the one upgrade that pays. Small-lot operators working 500 to 1,000 miles are delighted to be in the game, and the founder routinely works about 1,000 miles on 160 and 2,500 on 80 from a Greyline.
Strongest band — the band where this height's NEC model shows its highest gain. A bonus where physics and geometry align, not a requirement — the bands beside it still carry real gain, and every band works.
EDZ (Extended Double Zepp) — when your antenna is electrically long on a band, the radiation pattern develops multiple lobes. Not worse, just different. See the physics notes below.
Wind rating — the published ASCE 7-10 rating for each height. The flag is the dominant wind load, so lowering it in high wind moves you to the flag-down rating. Longer whips add drag and moment.
The Physics, in Five Minutes
Your antenna's job is to take electrical energy from your transmitter and turn it into radio waves that travel toward operators you want to reach. How well it does that depends on geometry — the antenna's height relative to your operating wavelength — and what's around it.
Greyline VDAs have an elevated feedpoint, which decouples them from the soil losses that limit ground-mounted verticals. But ground type still shapes the pattern. Saltwater reflects efficiently. Average soil absorbs more energy. A hill changes your takeoff angle without changing the antenna itself.
Height is aperture: more of it means more signal on the low bands, and it moves the bonus gain down the dial. In NEC modeling, a 20 ft antenna is strongest on 10 meters, a 24 ft on 10–12, and the 28 ft and the Skylines on 17. On every other band it still radiates well with a tuner — just without the extra bonus.
EDZ — Extended Double Zepp Behavior
When your antenna is electrically long
When the electrical length of an antenna grows long enough on a given band, the radiation pattern shifts. Instead of one strong lobe at a low takeoff angle, the antenna develops multiple lobes — some at higher angles, some at lower angles. This is called EDZ behavior, after the Extended Double Zepp antenna, which shows the same physics.
An EDZ pattern isn't worse — it's different. The higher-angle lobes favor shorter, regional paths; for DX, one of the lobes may point exactly where you need it, or the energy may spread across angles that don't match the band's propagation that day.
The calculator marks configurations where the NEC modeling shows EDZ behavior on a band. Worth knowing, not worth fearing — the antenna still works; the pattern is just more complex. Jon, KL2A, and many other owners run the taller builds and enjoy 10, 12, and 15 meters in the EDZ region, while the bonus moves down the bands as the solar cycle comes off its peak.
Wind ratings are the published ASCE 7-10 figures for each Greyline height: 2-inch 6061-T6 aluminum at a stated height, flag up and flag down. Adding a whip extends the moment arm; the flag adds drag area. The numbers are what they are.
For a deeper read on any of this, see The Bookshelf — Zavrel's Antenna Physics, Kraus, Cebik, and the authorities we read from.
