BoatsExplained.com - VHF aerial

Losing your VHF aerial is the maritime equivalent of being struck dumb. So why not make yourself a back-up?
EVERYONE ought to have an emergency aerial, but they cost money and spend their life in a dark corner of the spares locker. An alterrlative for the poverty-stricken yachtie. is a DIY half wave dipole. It's so simple that in a real life emergency, a useable aerial could be lashed up from the remnants of your old one.
Start with a suitable length of coaxial cable (see component list). This will most probably have an impedance of either. 50 or 75 ohm. Check the specification in your radio's instruction manual. Then follow the sequence shown in Figure 1. Strip about 500mm (20in) off the outer insulation to expose the braid. Remove all but a couple of inches and twist the remainder together before soldering. Next, trim the inner core in its plastic sheath until it's 445mm (17.5in) long. Tin one end of the copper piping with solder. Copper is such an efficient heat conductor that it's unlikely your soldering iron will cope. Try heating the pipe with a blowtorch or over the kitchen stove, but remember to wear an oven glove.
Once the tinned piping has cooled, slide it up the coaxial cable until the tinned end meets the braid. Solder the braid to the copper piping. Insert the aerial into the plastic piping and seal the ends with plastic putty. Put a plug that fits your radio to the end of the coaxial cable and you have an aerial. Although a half wave is omnidirectional, it's most sensitive to signals coming in at right angles to the aerial wire. This means that normally it will work better sticking up vertically when its performance will be comparable to most aerials.

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