Yesterday, we posted this quiz from the November 1956 issue of QST. You have a 99-conductor cable, unlabeled, and you need to mark the conductors. If you have only a buzzer and battery, how many round trips will you need to make?

That issue of QST promised that the answer would be published “next month,” but I couldn’t find it. The December issue talked about the October quiz, and there was nothing in the January issue. So much to the consternation of 1956 hams, the solution was never pHappy Valentine’s Day! | OneTubeRadio.comublished.

Fortunately, we now have this internet thingie, and it’s possible to find answers to questions like this. It turns out the puzzle was originally authored by Martin Gardner, the Scientific American puzzle columnist, and editor of Humpty Dumpty’s magazine. Only one round trip is necessary. Here’s the full solution:

DX4U can identify and label all 99 conductors with just 1 round trip (Side A → Side B → Side A) across the chasm.

Step 1: At Side A (Starting End)

1. Pick any single conductor and leave it isolated. Label it Wire 1.
2. Take the remaining 98 wires and twist them into 49 separate pairs:
   • Pair 1, Pair 2, Pair 3, …, Pair 49.

(At this stage, Side A has one isolated reference wire and 49 independent closed loops.)

Step 2: First Trip (Cross over to Side B)

DX4U crosses the chasm with the battery and buzzer tester:

1. Find Wire 1: Test continuity across combinations of wires. Exactly 49 pairs will buzz, leaving one single conductor that shows no continuity to any other wire. That isolated conductor is Wire 1. Label it 1.
2. Map the 49 pairs: The buzzer quickly identifies which wires belong together in the 49 pairs. Label these pairs arbitrarily:
   • (A₁, B₁), (A₂, B₂), …, (A₄₉, B₄₉).
3. Daisy-chain the wires in series: Connect the pairs into one long chain:
   • Connect Wire 1 to A₁.
   • Connect B₁ to A₂.
   • Connect B₂ to A₃.
   • … continue chaining until B₄₈ connects to A₄₉.
   • Leave B₄₉ unconnected.
4. Label Side B permanently in order:
   • Wire 1 → 1
   • A₁ → 2, B₁ → 3
   • A₂ → 4, B₂ → 5
   • …
   • A₄₉ → 98, B₄₉ → 99

Side B is now completely identified and labeled!

Step 3: Second Trip (Return to Side A — Completing 1 Round Trip)

DX4U returns to Side A and untwists all 49 pairs made in Step 1.

1. Trace from Wire 1: Using the battery and buzzer, test from known Wire 1 against all loose ends. The one wire that buzzes is connected to Wire 1 across the chasm, so it must be Wire 2.
2. Decode Wire 2’s partner: Because Wire 2 was originally twisted with a specific partner wire in Step 1, its old partner is instantly known to be Wire 3. Label it 3.
3. Trace the rest of the chain:
   • Test from Wire 3 to find the wire that buzzes → that is Wire 4.
   • Its original Step 1 partner is Wire 5.
   • Repeat down the line until all 99 wires are labeled.

Every single conductor is now uniquely identified at both ends after exactly one round trip.