If you’re hunting for a high-performance antenna that doesn’t look like a metallic porcupine, the Hourglass Loop (popularized by KE4ERO) is a fantastic weekend project. It is essentially two delta loops stacked and fed in-phase, resulting in a bidirectional pattern with about 5 dB of gain over a standard dipole.
Unlike a typical 1-wavelength loop, the hourglass uses a 2-wavelength wire. The crossing point in the center acts as a phasing section, forcing currents in the top and bottom horizontal segments to be in phase. This creates a narrow vertical radiation pattern that puts your signal exactly where it needs to be: on the horizon.
Hourglass Loop Antenna – Dimensions for VHF and UHF Bands
To get you on the air quickly, use the following dimensions as your starting point. These are calculated for the “weak signal” portions of the bands (SSB/CW/Data). Remember the ham’s golden rule: “Cut long, tune short.”
Note: The wires cross in the center but must not touch. Use a non-conductive spacer to ensure they remain separated.
Recommended Materials
You don’t need a machine shop to build this. Most of these items are likely in your junk box or at the local hardware store:
- Radiating Element: Use #14 AWG solid copper wire for 2m and 1.25m. For the 70cm version, #14 bare copper or even 3/16″ aluminum tubing provides excellent rigidity.
- Central Insulator: A small scrap of Plexiglass, Lexan, or UV-stabilized PVC board.
- Support Mast: 1-inch PVC pipe or a fiberglass telescoping pole. Avoid metal masts near the antenna elements to prevent de-tuning.
- Hardware: Stainless steel nuts, bolts, and wingnuts for the feedpoint to prevent corrosion.
- Feedline: 50-ohm RG-58 or RG-8X for short runs. For UHF, consider LMR-400 to minimize line loss.
Tuning and Performance
The Hourglass is natively close to 50 ohms, making it very “direct feed” friendly. Once assembled, check the SWR at your target frequency. If it is resonant too low, trim equal amounts from the top and bottom horizontal wires. If the impedance is slightly off, you can “squish” or “stretch” the hourglass shape slightly to find the 50-ohm sweet spot.
Expect a bandwidth of about 2-3 MHz under 2:1 SWR—plenty of room for the entire weak-signal portion of the band.
Hourglass Loop Feed Point
The magic of the Hourglass Loop lies in its symmetry. Because it is a balanced antenna system, the way you connect your feedline is the difference between a high-performance radiator and a piece of wire that just makes your coax shield part of the antenna.
1. Direct 50-Ohm Connection
The KE4ERO Hourglass is specifically designed to have a feed point impedance very close to 50 ohms when built to the specified height-to-width ratio.
- Location: The antenna is fed at the exact center of the bottom horizontal wire.
- Polarization: Feeding it here results in horizontal polarization, which is the standard for weak-signal SSB, CW, and FT8 work on VHF/UHF.
- No Tuner Required: If your dimensions are correct, you should see an SWR of 1.2:1 or better at resonance without any external matching networks.
2. The “Choke” Balun (Highly Recommended)
Since you are likely using unbalanced coaxial cable (like RG-58 or LMR-400) to feed a balanced antenna, “common mode” currents can travel back down the outside of your coax. This causes noise in the shack and distorts the antenna’s radiation pattern.
- The Simple Fix: Create a “Ugly Balun” or air-choke by coiling 5–7 turns of your coax into a 2-inch diameter circle right at the feed point.
- The Professional Fix: Use 3 to 5 snap-on ferrite beads (Mix 31 or Mix 43) on the coax immediately where it meets the antenna. This “chokes” off the RF and keeps your pattern clean.
3. The Center Insulator & “Crossing” Point
The feed point and the center crossing point are the two most critical mechanical areas:
- The Feed Point Block: Use a piece of UV-resistant plastic (like a scrap of cutting board or PVC plate). Secure the coax so that the weight of the cable doesn’t pull on the solder joints or wire elements.
- The Center Crossing: Remember, the wires must not touch where they cross in the middle. They should be separated by about 0.5 to 1 inch. You can use a small plastic spacer or simply zip-tie them to opposite sides of your non-conductive mast.
4. Weatherproofing
VHF/UHF frequencies are sensitive to moisture and oxidation.
- Seal the Coax: Use “Coax Seal” or silicone RTV to completely cover the point where the coax jacket is stripped away. If water gets into your coax braid, your SWR will drift every time it rains.
- Connections: Use stainless steel hardware. A light coating of conductive grease (like Penatrox) on the wire-to-terminal connections will prevent the “diode effect” caused by oxidation over time.
This video provides a practical look at how the hourglass loop is constructed and tuned, offering a helpful visual guide to complement the measurements in the table.
Related Posts