Turnstile Antenna
The Turnstile crosses two straight half-wave dipoles at 90 degrees and feeds them 90 degrees out of phase, producing circular polarization and a broad, nearly omnidirectional pattern favoring the horizon. George Brown developed it at RCA in the 1930s for FM and TV broadcast use, and it's stayed in the amateur toolkit ever since for general-purpose VHF coverage, APRS, and base-station work where you want solid coverage in every compass direction without a rotator.
Two straight dipoles, 90 degrees apart, 90 degrees out of phase
Each element is a plain straight half-wave dipole - no bending, no reflector. Crossing two of them at right angles and feeding them with a 90-degree phase difference produces a circularly polarized signal with a broad pattern that's close to omnidirectional around the horizon, which is exactly what a broadcast station (or an amateur base station) wants for even coverage in every direction.
-> circular polarization, horizon-favoring omnidirectional pattern
How this differs from the Eggbeater already on this site
The Eggbeater takes this same crossed-dipole, quadrature-fed concept and bends the elements plus adds a reflector screen to push the pattern toward zenith for satellite work. The Turnstile keeps the elements straight and skips the reflector, keeping the pattern favoring the horizon - the right tool for general omnidirectional coverage rather than overhead satellite passes.
- Turnstile (this guide): straight elements, no reflector, horizon-favoring pattern.
- Eggbeater: bent elements plus reflector screen, zenith-favoring pattern for satellites.
Why circular polarization for general coverage too
Even for ground-based, non-satellite use, circular polarization sidesteps the deep signal nulls that can happen between a horizontally and vertically polarized station when their orientations don't match - useful for APRS, packet, and general VHF coverage where you don't control the polarization of every station you're working.
Why it was originally a broadcast antenna
George Brown's original turnstile design solved a real broadcast engineering problem: FM and early TV stations needed a horizontally polarized, omnidirectional pattern from a mast-mounted antenna, and stacking several turnstile bays vertically gave broadcasters additional gain while keeping that same omnidirectional coverage - the same stacking principle amateur builders sometimes borrow for a gain version of this design.
Installation options
- Mast-mounted base station: the standard install — as high as practical for good horizon-to-horizon coverage.
- Stacked bays for added gain: multiple turnstiles stacked vertically, phased together, add gain while preserving the omnidirectional pattern — the same principle broadcast stations use.
- APRS digipeater/base coverage: a common practical use case where consistent omnidirectional coverage matters more than beam gain in any one direction.
| Parameter | 2m (146 MHz) | Notes |
|---|---|---|
| Each straight dipole (total length) | ~38.9 in (0.99 m) | Standard half-wave length, no bending |
| Phasing line length difference | ~9.4 in electrical (0.25 lambda x VF) | Sets the 90-degree quadrature phase shift between elements |
| Mounting height above surroundings | As high as practical | Standard VHF siting guidance - height matters more than fine pattern shaping here |
Turnstile Dimension Calculator
Materials for Turnstile
Building the Turnstile
A simple build - two straight dipoles crossed at a center point, with the quadrature phasing feed as the one detail that needs care.
Cut both dipole elements
Use the calculator above to get the standard half-wave length for your design frequency, and cut two identical straight elements.
Cross-mount the elements at 90 degrees
Mount both straight dipoles to a non-conductive center support, crossed at 90 degrees to each other at a common feedpoint height.
Build and connect the quadrature phasing feed
Wire the phasing line/power divider so one dipole is fed a quarter-wavelength (electrically) different from the other.
Connect coax and mount to your mast
Connect your feedline and mount the assembled antenna to a fixed mast at your best available height.
Sweep SWR and check coverage
Sweep the feedpoint for a clean resonant dip, then check real-world coverage across the compass directions you care about.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| Coverage is uneven in some directions | Elements not truly at 90 degrees or mounted at different heights | Check the alignment and mounting height of both elements | Correct alignment; misalignment distorts the intended omnidirectional pattern |
| SWR is off from the calculated frequency | Elements cut to different lengths | Confirm both elements were cut to identical lengths | Re-cut for matched lengths; asymmetry affects phase balance and resonance more here than on a single dipole |
| Weak signal directly overhead | Design inherently favors the horizon over zenith | Compare signal strength at zenith vs. horizon | Expected behavior; use the Eggbeater guide instead for zenith/satellite coverage |
How is this different from the Eggbeater already on this site?
The Eggbeater bends its elements and adds a reflector to favor zenith for satellite work. This Turnstile keeps the elements straight with no reflector, favoring the horizon for general omnidirectional coverage.
Do I need a rotator?
No - the whole point of this design is broad, roughly omnidirectional coverage from a fixed mount.
Why circular polarization for ground-based work?
It avoids the deep signal nulls that can occur between mismatched horizontal/vertical stations, which is useful for APRS, packet, and general VHF work where you don't control other stations' polarization.
Can I stack multiple turnstiles for gain?
Yes - this is a classic broadcast-antenna technique that carries over well to amateur use, adding gain while keeping the omnidirectional pattern.
Where did this design come from?
George Brown developed it at RCA in the 1930s for FM and TV broadcast antennas, and it's been part of the general antenna toolkit ever since.
Can I build this for bands other than 2m?
Yes, the calculator scales dimensions to your chosen design frequency.