# Build a Directional Antenna

Part of the Radio Merit Badge Digital Resource Guide: [Introduction & Overview](https://merit-badge.university/merit-badges/radio/guide/index.md)

*8. Option D: Direction Finding*

> **8d3.** Build a simple directional antenna for either of the two frequencies used in ARDF.

## The Tape-Measure Yagi (2 Meters)

The most popular Scout-friendly ARDF antenna project is the **tape-measure Yagi** — a three-element directional antenna made from inexpensive steel tape measures and PVC pipe. It's lightweight, collapsible, and effective.

### Materials

- 3 steel tape measures (at least 40 inches each) — dollar store tape measures work fine
- 1 PVC pipe, 3/4" diameter, about 36" long (the boom)
- 3 PVC cross fittings or hose clamps to mount the tape-measure elements
- 1 BNC or SO-239 connector (to connect the coax cable)
- Short length of RG-58 coax cable with appropriate connector for your receiver
- Electrical tape, zip ties, or hose clamps
- A hacksaw for cutting PVC

### Element Dimensions (for 146 MHz)

| Element | Length | Position on Boom |
|---------|--------|-----------------|
| **Reflector** | 41.5 inches | 0 inches (back end) |
| **Driven element** | 35 inches (two halves, 17.5" each, with gap at center) | 12 inches from reflector |
| **Director** | 33 inches | 24 inches from reflector (12 inches from driven) |

![Labeled diagram of a tape-measure Yagi antenna showing reflector, split driven element, director, boom spacing, and coax connection](https://ik.imagekit.io/doulacoop/tr:w-800/mbu-assets/merit-badges/radio/guide/tape-measure-yagi-layout?v=3ed66dc8)

### Assembly Steps

1. **Cut three tape-measure strips** to the lengths above. Round or tape the cut ends to prevent sharp edges.
2. **Mount each strip** to the PVC boom at the positions listed, using cross fittings or hose clamps. Elements should be perpendicular to the boom.
3. **The driven element** is split into two halves with a gap at the center. Connect the coax cable center conductor to one half and the shield to the other half.
4. **Attach the coax connector** and run a short cable to your receiver.
5. **Test:** Point the antenna at a known VHF signal source and verify that the signal is strongest when the director end points at the source.

> **Safety First!**
>
> Cut tape-measure edges are razor-sharp. Always round or tape the ends. Wear gloves during cutting. An adult should supervise the cutting step.

> **Tip**
>
> Search online for "tape measure Yagi ARDF" for detailed build guides with photos. The ARRL and many ham radio clubs publish step-by-step instructions specifically designed for Scout projects. Your merit badge counselor or a local ham may also have a build session planned.

Video: [Tape Measure Yagi Beam Antenna - Ham Radio Q&A — KB9VBR Antennas](https://www.youtube.com/watch?v=BmHoQrDfw-0)

[Tape Measure Yagi Antenna — WB2HOL](https://www.eham.net/article/26905): One of the most popular tape-measure Yagi build guides, with detailed dimensions and construction photos.

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