AIS to check VHF range
While hopefully the myriad ‘radio check’ calls to the coastguard are being directed to other resources such as marina and harbour offices and the worthy National Coastwatch Institution, many sailors still worry whether their VHF transmissions are of adequate strength to be heard at distance in an emergency situation. Aerial degradation is a common reason for weak transmissions; a radio check may prove short-range clarity as you leave harbour, but the development of an eerie silence as the shore recedes may indicate system underperformance. If your handheld VHF has clearer and further reaching transmission than your masthead VHF you have a problem. Fairly cheap aerial test meters are available; I have one and it did indicate sub-optimal function. Those yachtsmen who have an AIS unit wired through a splitter using the main VHF aerial have another way of checking that the antenna is in good order; the AIS range is a good display of VHF range. Both a yacht on which I crossed the Atlantic and my own boat had aerial faults that resulted in a reduced AIS target detection of only a few miles. This correlated well with my VHF radio range; when the mast was down for re-rigging I installed a new aerial and cable which brought both my VHF and AIS function back up to over 20 miles. The lesson learnt is that if your AIS range drops (when a splitter is part of the system) check your VHF range too. Out of interest, I checked my emergency VHF antenna; when I plugged it in and held it aloft its AIS range proved to be a mere four miles – rather disappointing.