Bobtail Curtain (and Sterba Curtain)
A Bobtail Curtain wires three quarter-wave verticals into one continuous conductor: up the center element, across a horizontal top wire in both directions, and back down each outer element to a shared ground system. That single wire path automatically sets the correct current phase between the three elements — no external phasing harness required — and with the elements spaced a half-wavelength apart, the result is real bidirectional broadside gain and a low radiation angle that low-band DXers value on 80m and 40m. This guide also covers its historical cousin, the Sterba Curtain, as a related but distinctly larger design.
How the wire path itself sets the phase
Trace the current path: up the center quarter-wave vertical, out along the top "clothesline" wire in each direction, then down each outer quarter-wave vertical to the shared ground system. Because the top wire's current effectively reverses direction relative to the center element by the time it reaches each outer element, the two outer verticals end up driven out of phase with the center one — and because they're also spaced a half wavelength away from center, that phase reversal plus that spacing combine to reinforce broadside instead of canceling. The wire's own geometry does the phasing job that a separate phasing harness would otherwise need to do.
Phase reversal (from the wire path) + half-wave spacing -> broadside reinforcement, no external phasing line
Why it's valued for low-band DX specifically
Three phased verticals working together give a genuinely lower radiation angle than a single vertical or a horizontal dipole at typical amateur heights, which matters most on 80m and 40m where getting energy out at a low angle is the biggest single lever on DX performance. The bidirectional broadside pattern favors two opposite directions rather than being a directional beam, so orient the curtain's broadside line toward your priority DX path.
The ground system still matters
Because the center element is fed against a ground/counterpoise system, and the two outer elements' bases bond to that same system, the antenna's real-world performance depends on a reasonably good ground or radial system at the base — the same dependency any ground-mounted vertical has. This design doesn't eliminate the need for a ground system; it eliminates the need for a separate phasing harness between the elements, which is a different, more specific advantage.
The Sterba Curtain — a related, larger cousin
Developed by E.J. Sterba at Bell Labs for early shortwave broadcast use, the Sterba Curtain applies the same in-phase multi-vertical-section principle but folds the wire into a continuous, fully insulated loop (no ground connection needed at all) with more radiating sections for higher gain. It's a genuinely bigger, more complex structure than a Bobtail Curtain and far less commonly homebrewed by hams today — mentioned here for historical context and comparison rather than as a build target of this guide.
- Bobtail Curtain (this guide): 3 elements, grounded base feed, moderate size, actively homebrewed by hams.
- Sterba Curtain: more sections, fully insulated loop, larger and historically a broadcast-scale design.
Installation options
- Three-mast layout: one mast per vertical element, connected by the top wire — the standard, most mechanically straightforward install.
- Single top support with guyed verticals: a single horizontal top support (like a long crossarm or catenary) carrying all three vertical wires down to individual anchor/ground points.
- Broadside orientation planning: since the pattern favors two opposite directions, plan the curtain's broadside line toward your priority DX path (or a compromise between two paths) before erecting supports.
| Parameter | 80m (3.75 MHz) | 40m (7.15 MHz) | Notes |
|---|---|---|---|
| Each vertical element | ~62.4 ft (19.0 m) | ~32.7 ft (10.0 m) | Quarter-wave height, all three elements equal |
| Spacing between adjacent verticals | ~131.2 ft (40.0 m) | ~68.8 ft (21.0 m) | Half wavelength — sets the broadside reinforcement |
| Total top-wire span (outer tip to outer tip) | ~262.4 ft (80.0 m) | ~137.6 ft (42.0 m) | Spacing x 2 |
| Ground/counterpoise system | At all three element bases | Same | Bond outer element bases to the same ground system as the fed center element |
Bobtail Curtain Dimension Calculator
Materials for Bobtail Curtain
Building the Bobtail Curtain
The wire path is simple; the ground system at all three bases is what most affects real-world performance, so don't shortcut it.
Erect the three vertical supports
Install three masts or supports at the calculated spacing, aiming for consistent height at all three.
Build the ground system at all three bases
Install ground rods and/or radial wires at each of the three support locations before running any wire, since this is what the finished antenna's performance depends on most.
Run the three vertical elements
Run each quarter-wave vertical wire from its base connection up to the top insulator at its support.
Connect the top wire across all three elements
Run the horizontal top wire from the outer element's top, across to the center element's top, and on to the far outer element's top, forming the single continuous conductor path.
Install the center feedpoint
Connect the coax center conductor to the base of the center vertical element and the shield to the ground system at that same point.
Bond both outer elements' bases to the ground system
Connect the base of each outer vertical element to the same ground system used at the feedpoint, keeping bonding connections short and solid.
Connect coax, sweep SWR, and verify the pattern
Connect your feedline, sweep for the resonant dip, and verify the bidirectional broadside pattern favors your intended DX headings.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| Gain and low-angle performance seem underwhelming | Weak or minimal ground system at one or more of the three bases | Check ground rod/radial coverage at all three element bases | Add ground rods or radials; this design's real performance depends heavily on the ground system |
| SWR is high and won't come down | Uneven element heights or a broken/loose top-wire connection | Check all three vertical heights and the top-wire connections at each support | Correct height evenness and re-solder any loose top-wire joints |
| Pattern seems to favor one direction unevenly instead of a clean bidirectional broadside | Nearby structures or terrain asymmetry, or an outer element ground connection issue | Compare ground connection quality between the two outer elements | Correct any imbalance in the outer elements' ground bonding |
Do I need a phasing harness like a phased vertical array?
No — that's the design's whole point. The wire path itself (up the center, across the top, down each outer element) sets the correct phase relationship automatically, without a separate phasing line network.
Do I still need a ground system?
Yes. This design eliminates the need for a phasing harness between elements, not the need for a ground/counterpoise system at the base — that still matters as much as it would for any ground-mounted vertical.
What's the difference between this and a Sterba Curtain?
The Sterba Curtain applies a similar phased-vertical-section principle but folds into a larger, fully insulated loop with more sections and no ground connection needed — a bigger, historically broadcast-scale design that's far less commonly homebrewed by hams today.
Which direction does the pattern favor?
Two opposite directions, broadside to the line of the three elements — plan your support layout with that broadside line pointed toward your priority DX path.
Is this a good design for 80m/40m specifically?
Yes, it's particularly valued there because the low radiation angle from the phased verticals matters most on the lower bands, where a single vertical or dipole's takeoff angle is often higher than ideal for DX.
How much real estate does this need?
A full-wavelength total span between the outer elements — on 80m that's roughly 260+ feet, on 40m roughly 135+ feet — plus three support points and a ground system at each.