Building a Half-Wave Dipole

A half-wave dipole is two pieces of wire totalling 143 divided by the frequency in MHz, split at the centre — here are the lengths and the hanging notes.

Start from the baseline: you do not need this antenna to begin. Shortwave broadcast transmitters commonly run 10-500 kW, so a simple 7-10 m wire already copies strong signals. The dipole is the refinement that matches your wire to one chosen band.

The cutting formula is 143 divided by the frequency in MHz, giving the total length in metres. Reference cuts: 15.2 m for 9.4 MHz in the 31 m band, 7.5 m for 19.1 MHz in the 19 m band and 5.9 m for 24.9 MHz near the 11 m band.

For night listening the same formula gives the lower-band cuts: about 19.5 m at 7.35 MHz in the middle of the 41 m band, and about 23.6 m at 6.05 MHz in the middle of the 49 m band. Cut the total length, then divide it into two equal legs — the 31 m dipole becomes two wires of about 7.6 m each.

Hang the two legs in a straight line, as high and as far from house wiring as practical, and feed them at the centre. Distance from household electronics matters because local noise, not weak propagation, is the most common reason a night band sounds dead.

Tuning is verification, not ritual: listen across the whole band, note where signals peak in the log with UTC time, and adjust only if the band edges clearly outperform the middle. Choose the band first with Shortwave Frequency Bands, time the broadcast with Shortwave Schedules in UTC, and the wire, the formula and the log together are the whole instrument.

• 31 m band, 9.4 MHz: 15.2 m total, two legs of 7.6 m
• 41 m band, 7.35 MHz: about 19.5 m total, two legs of about 9.7 m
• 49 m band, 6.05 MHz: about 23.6 m total, two legs of about 11.8 m
• 19 m band, 19.1 MHz: 7.5 m total, two legs of 3.75 m
• 11 m region, 24.9 MHz: 5.9 m total, two legs of 2.95 m

Further reading

• Shortwave Frequency Bands
• Shortwave Schedules in UTC