Build a Portable Tape Measure Yagi Antenna
The tape measure Yagi is the definitive fox hunting and ARDF (amateur radio direction finding) antenna — a 3-element 2m beam built entirely from a cheap hardware store tape measure, a short PVC pipe boom, and a BNC connector. Introduced by Joe Leggio WB2HOL in QST and refined by countless builders since, the design folds completely flat for transport, springs back to precise element dimensions in seconds, and delivers the sharp directional pattern needed to home in on a hidden transmitter through a forest at 50 paces. At under $10 in materials and one hour of construction, it is also the most accessible directional VHF antenna project in amateur radio — the one antenna that every ham who enjoys field operations should have in their kit.
Fox Hunting and ARDF
Fox hunting (hidden transmitter hunting) is the primary use for the tape measure Yagi. A hidden transmitter broadcasting on 2m FM is located by participants using directional antennas to zero in on the signal source:
- The antenna's role: point the Yagi in different directions and note where the signal is strongest. The Yagi's narrow 60° beamwidth allows bearing determination to within 5–10°. Walk toward the bearing, repeat, and triangulate to the hidden transmitter.
- The rear null: more useful than the forward beam for close-range fox hunting. When the signal is strong (you are close to the transmitter), the forward beam saturates your radio's S-meter. Rotate 180° — the deep rear null (20+ dB less signal) gives you a more precise bearing when close.
- ARDF on 2m: ARDF events run multiple foxes simultaneously at 80m and 2m. The 2m tape measure Yagi is the standard antenna for the 2m ARDF discipline worldwide. Events are held as foot races — the compact folding design and light weight (under 4 oz) make it genuinely usable while running through the woods.
- Emergency locating: locating a downed aircraft ELT (emergency locator transmitter) or a personal locator beacon requires the same skills as fox hunting. Many ARES/RACES groups train with tape measure Yagis for this reason.
Satellite, Portable, and SOTA Operation
The tape measure Yagi's deployability makes it useful well beyond fox hunting:
- Satellite operation (hand-held): the tape measure Yagi is light enough to hand-hold and manually track a satellite pass across the sky. For FM satellite contacts through SO-50, AO-91, and similar satellites, a hand-held tape measure Yagi replaces the need for a rotator setup. Point at the satellite and move with it — the wide beamwidth (60°) gives enough angular margin to maintain signal during a 10-minute pass without precise tracking.
- SOTA/POTA portable: packs flat in a daypack alongside the radio and fits in a car glovebox. Deployed in seconds at a summit or park, the tape measure Yagi provides enough gain for 2m SSB contacts on simplex or repeater access far beyond what a rubber duck provides.
- VHF contesting from a hilltop: pointed at population centers, a 3-element tape measure Yagi on a camera tripod at a hilltop location makes a competitive rover station for the ARRL VHF contests. The low investment and fast deployment justify including it in every portable VHF operating kit.
- Direction finding for interference: locating an interfering signal source on 2m — a jammed repeater, an RFI source, or an unauthorized transmitter — uses the same technique as fox hunting. The tape measure Yagi is the standard tool for this task.
Why Tape Measure for Elements
The tape measure Yagi uses flat steel tape measure blade for its elements — the same spring-steel ribbon inside a standard tape measure:
The WB2HOL Design — Why It Works
The WB2HOL tape measure Yagi uses a 3-element design optimized for wide front-to-back ratio and a strong rear null rather than maximum forward gain. This prioritization is deliberate for direction-finding use:
| Element | Length (inches) | Length (mm) | Position on boom from reflector | Notes |
|---|---|---|---|---|
| Reflector | 41.5 in | 1054 mm | 0 in (rear) | Longest element — rear of boom; start with 42 in, trim slightly |
| Driven element | 35.5 in | 902 mm | 17.75 in from reflector | Split at center for feedpoint; uses T-connector or hairpin match |
| Director | 33.875 in | 860 mm | 35.25 in from reflector | Shortest element — front of boom |
| Total boom length | ~38 in (3.2 ft) | ~965 mm | — | 3/4-inch schedule 40 PVC; 40-inch piece provides margin |
Portable Tape Yagi Calculator
Materials for a 3-element 2m tape measure Yagi — complete fox hunting kit
The Driven Element Feedpoint Challenge
The 3-element Yagi's driven element presents approximately 25–35 Ω at the feedpoint — too low for direct 50 Ω coax connection. The tape measure Yagi uses one of two simple matching approaches:
Driven Element Split and Coax Connection
The driven element blade passes through a PVC tee fitting on the boom, with a deliberate gap at the center for the feedpoint. The coax connects here:
Building the Tape Measure Yagi
Total build time is 45–90 minutes. The most time-consuming parts are cutting the tape blade cleanly and installing the feedpoint BNC. Everything else is PVC fitting and zip tie work. No soldering is required if using a pigtail approach for the feedpoint — this is genuinely a no-solder build for experienced builders.
Disassemble the Tape Measure and Cut Blade Sections
Open the tape measure case and remove the full blade. Using tin snips, cut three sections from the blade according to the dimensions table. Always wear safety glasses when cutting spring steel tape blade — cut ends spring sharply and can cause eye injury:
Prepare the PVC Boom and Mark Element Positions
Cut the 3/4-inch PVC pipe to 40 inches. Mark three element positions measured from the REAR (reflector end) of the boom:
Install Reflector and Director
Insert the reflector blade through the tee side port at the rear boom position and the director through the tee at the front position. These are the parasitic elements — no feedpoint connection needed:
Install Driven Element and Feedpoint BNC
The driven element installation is the most involved step — the two blade halves must be centered with a gap at the middle, and the BNC connector must connect to each half independently:
Initial SWR Check
Hold the assembled antenna horizontally at arm's length, pointing away from you, with the director end forward. Connect the NanoVNA or radio and check for a usable SWR on 2m FM:
Field Deployment and Fox Hunting Technique
Deploying the tape measure Yagi in the field is a one-minute operation. The fox hunting technique requires understanding both the front beam and the rear null:
Why You Need an Attenuator
The tape measure Yagi without an attenuator is useless for close-range fox hunting. When the signal is strong, the radio's S-meter pins at maximum in all directions — you cannot find the bearing because the signal is equally "full" pointing in every direction. The attenuator reduces signal strength to the level where directionality is again visible on the S-meter:
The Body Shielding Technique
When very close to the hidden transmitter (within 15–20 meters), even the maximum attenuator stack saturates the radio. At this point, turn the antenna off and use your own body as a directional shield:
- How it works: the human body absorbs approximately 20–30 dB of VHF signal from one side while passing signals from the other. Rotating while holding the radio against your chest finds the null direction — when the signal drops, the transmitter is directly behind you.
- Technique: hold the handheld radio against your chest with the antenna down. Rotate slowly. When the S-meter drops, the transmitter is in the direction you are facing away from — turn around and look.
- Practice this: body shielding works best after practice. The null is about 30–40° wide on a human body and needs to be interpreted — the exact center of the null is behind you at your center of mass, not at either shoulder.
- Combined sequence: most experienced fox hunters use the Yagi at distance, the rear null at medium range, and body shielding for final close-in location. The transition between techniques is fluid with practice — carry all three capabilities from the start of every hunt.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| No directional pattern — signal equally strong in all directions | Radio S-meter saturated — signal too strong at current range | Add 10 dB attenuator — if pattern appears, saturation was the cause | Use progressively more attenuation until directionality is visible; add attenuators in 10 dB steps |
| High SWR — radio transmit power reduced or fault indicator | Blade halves touching at feedpoint gap, or coax connections reversed | Check gap between driven element halves — must be 0.5 inch open circuit | Separate blade halves to restore gap; verify coax center to one blade, shield to other |
| Pattern seems to point backwards — null where gain should be | Antenna mounted backwards — director pointing toward transmitter | Identify which end is the director (shorter element) — that end should point toward the signal source | Rotate antenna 180° — director end toward transmitter gives maximum signal |
| Elements spin in tee fittings — pattern changes randomly | Tape blade not secured in tee ports | Check tape blade friction fit in tee port — should resist rotation by hand | Wrap 4–6 layers of electrical tape on blade at tee port contact point; add zip tie over tee and blade for additional security |
| Elements sag — not staying horizontal | Tape blade installed wrong side up — concave side should face up for flattest deployment | Check which side of the tape blade faces up — the concave (curved) side is the inside of the coil | Remove and re-insert blade with the flat (printing) side down and curved side up; blade should spring flat and stay flat |
| Antenna works well initially but elements grow shorter over hunts | Tape blade sliding through tee ports — dimension changing during transport | Measure element lengths before each hunt — compare to original dimensions | Add a piece of electrical tape wrapped around blade as a stop-tab at each tee port exit; prevents blade sliding inward |
What frequency is this antenna designed for?
The WB2HOL dimensions in this guide are optimized for 146.565 MHz — the national 2m fox hunting frequency used by most clubs in North America. The antenna performs well across the entire 2m FM band (144–148 MHz) — SWR below 2:1 from band edge to band edge — so it works equally well for fox hunts on any 2m FM frequency, satellite operation on 145–146 MHz, and simplex contacts on 146.52 MHz. If your local fox hunting events use a different frequency (some clubs use 144.200 MHz or specific repeater output frequencies), the antenna still works acceptably with no modification — the 2m band is narrow enough that the WB2HOL dimensions are usable from 144.0 to 148.0 MHz without adjustment.
Can I build a 70cm version for ARDF events?
Yes — scale all dimensions by 146/440 = 0.332. The reflector becomes 13.8 inches, driven element halves become 5.9 inches each, director becomes 11.2 inches, and element spacings scale to 5.9 inches (reflector to driven element) and 11.7 inches (reflector to director). Total boom length approximately 12.6 inches. A 70cm tape measure Yagi from a 12-foot tape measure is extremely compact — the entire antenna folds to a 13-inch bundle. The same fox hunting technique applies on 70cm, but the beamwidth is narrower (approximately 45° at 70cm for a 3-element design), requiring more precise pointing for bearing determination.
How do I carry this antenna during a fox hunt on foot?
Two common carrying methods: retracted for walking, deployed for searching. When walking toward a bearing, fold the elements back along the boom (the tape blades fold naturally alongside the PVC pipe), holding the whole bundle in one hand. When stopping to take a bearing, shake the boom horizontally and the elements spring outward to their deployed positions automatically — a characteristic of the spring-steel tape blade that experienced fox hunters consider one of the antenna's most elegant features. Alternatively, some operators deploy the antenna fully and simply carry it horizontally in one hand while walking, director forward, listening for signal changes as they move. This continuous monitoring while moving is more advanced but allows real-time bearing updates without stopping.
Why is the WB2HOL design used instead of a more gain-optimized Yagi?
For direction-finding the figure of merit is front-to-back ratio and null sharpness, not forward gain. A gain-optimized 3-element Yagi produces maximum forward gain at the expense of a shallower rear null — useful for contacts but suboptimal for DF work. The WB2HOL dimensions deliberately sacrifice approximately 0.5–1 dBd of forward gain to achieve a deeper, more sharply defined rear null. This deeper null allows more precise bearing determination at medium range — the key operational requirement for fox hunting. Additionally, the wider 60° forward beamwidth of the WB2HOL design makes it easier to sweep during a hunt without missing bearings through too-narrow pointing — an ergonomic advantage when rotating the antenna quickly while walking.
How accurately can I determine a bearing with this antenna?
Using the forward beam maximum, bearing accuracy is typically ±10–15° for an experienced operator — sufficient for triangulating a hidden transmitter from two positions 100+ meters apart. Using the rear null minimum, accuracy improves to ±5–8° at medium range. The body shielding null provides approximately ±15° but at very close range (under 20 meters) where the large angular error is still acceptable for locating the transmitter visually. In formal ARDF competition, experienced competitors determine bearings to within 5° using the rear null and navigate to within a few meters of the transmitter in forested terrain. The limiting factor is usually propagation (multipath from terrain and vegetation creating false bearings) rather than antenna directivity.
Can I use this antenna for satellite contacts?
Yes — the tape measure Yagi is popular for hand-held satellite operation. Its light weight (under 4 oz complete) and compact design make it comfortable to hold and manually track during a satellite pass. For FM satellite contacts through SO-50, AO-91, or similar FM birds, point the antenna at the satellite's approximate position in the sky and follow it across the pass. The 60° beamwidth is forgiving of pointing errors, and manual tracking by ear (move toward the peak signal) is easy in practice. The antenna's 7+ dBd gain provides a significant advantage over the rubber duck for weaker passes at low elevation angles. For SSB linear transponder satellites where more precise pointing is needed, the tape measure Yagi is a starting antenna — more elements improve pointing accuracy for linear satellite work.