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Unit 13: License + Fox Hunt

Both kids earn their own ham radio licenses. Then we build the gear to find a hidden transmitter, and go hunting.

Sessions: 6+ (license study runs in parallel with the other units) · Cost: ~$60 · Badges: 📻 Licensed, Radio Operator Prerequisites: Unit 12 (and the motivation it creates!)

Part A: Technician licenses

  • There's no minimum age. Kids as young as 5 have passed. An 11 y.o. is very realistic; an 8 y.o. is realistic with enthusiasm.
  • 35 questions from a public pool of about 400. Passing is 26 correct.
  • The pool is published, so study it.
Tool How
HamStudy.org Free flashcards with spaced repetition. 10–15 minutes a day.
ARRL Ham Radio License Manual Explains the "why", so it's not just memorizing
This workshop Units 1–12 already covered Ohm's law, resonance, antennas, and frequencies
Local club VE session ARRL VEC, Laurel VEC, or GLAARG, some online. There's a small fee; many clubs waive it for kids.

Plan: - 11 y.o.: HamStudy daily; aim for a practice-exam average of 85 % or more before booking. - 8 y.o.: start with the sections that connect to what they've built (safety, electrical principles, operating). Book the exam when their practice scores clear the pass mark consistently. No pressure. It's okay to go second. - Celebrate each callsign on the day it appears in the FCC database.

Part B: fox hunt gear

Radio direction finding (RDF), also called fox hunting, T-hunting, or ARDF: someone hides a transmitter (the "fox"), and hunters find it with directional antennas.

1. Tape-measure Yagi (both kids)

  • The classic WB2HOL design: steel tape-measure elements on a PVC boom, 3 elements for 2 m.
  • Get the exact dimensions and hairpin match from the original WB2HOL article (search "WB2HOL tape measure beam"). Don't trust copies with typos.
  • Tape-measure edges are sharp. Cover the ends with tape or end caps. Gloves while cutting.
Job 8 y.o. 11 y.o. Parent
Cut PVC and tape Measures, marks Cuts the PVC Cuts the tape (snips, gloves)
Assemble Hose clamps Hairpin match, solders the coax Checks
Tune SWR with a NanoVNA

2. Offset attenuator (11 y.o.)

  • Close to the fox, the signal is so strong it comes in from every direction and the Yagi can't point.
  • An offset attenuator mixes the signal with a local oscillator, so you listen off frequency and turn a knob to weaken it smoothly by 100 dB or more.
  • Design and kits: homingin.com (K0OV) has the details.
  • A through-hole build that fits right after Unit 4.

3. The fox transmitter

flowchart LR
    pico[Pico] -- "tones / CW ID<br/>(audio via cap + divider)" --> mic[HT mic input]
    pico -- "PTT via 2N3904 or opto" --> ptt[HT PTT]
    batt[(Battery)] --> pico & ht[📻 Cheap HT<br/>low power]
    mic --- ht
    ptt --- ht
  • Radio: a cheap HT on low power. The controller keys its PTT and feeds audio.
  • Controller: a Pico.
  • It plays a tune (Unit 9 songs.py!) for 20–30 s, then sends the parent's callsign in Morse, then rests.
  • Or buy a fox controller kit.
  • Legal:
  • The fox must ID at least every 10 minutes (§97.119). Build the CW ID into the loop.
  • A licensed control operator is responsible for it the whole time.
  • Use a frequency your local club uses for T-hunts (146.565 MHz is common in the US; check your band plan).

Part C: the hunt

  1. Backyard practice: the parent hides the fox. The kids take turns: take a bearing, draw an arrow on a map, walk, take another bearing. Where the arrows cross is the fox.
  2. Park hunt: bigger, with a timer. Swap roles: one kid hides the fox.
  3. Club hunt: many ham clubs hold them. Kids who show up with a homemade Yagi get a lot of attention.

Talk about it

  • Why does the signal seem to come from everywhere when you're close?
  • Rescuers find lost hikers' beacons and downed aircraft this way. How is our hunt the same?