Here’s how we make an AIS tuned 3dB gain VHF aerial using RF-coax cable.
Buy a 5 or 10m length of 50 ohm RF coax cable with bnc connectors already attached – this makes two – http://www.amazon.co.uk/dp/
B00JVUP0L4. Cut to required length. Strip back the outer coating at the cut end to a length of 44.4cm + 5cm to make a loop (1/4wave for AIS frequencies). Pull the inner core through the outer sheath and lay the outer sheath back along the length of the coax and trim to 44.4cm. I add a couple of cm to the length so I can bend the tip of the inner core back on itself to hook it over something. Make sure the length of the inner is 44.4cm excluding the looped over end. Cover in heat shrink wrap if you want to make it waterproof and you have a 3dB gain AIS Aerial.
There is a useful video here showing how to do it here :-
and a photo of a 5m long one we made earlier. This one had a range of over 25NM when we put it on the 20th floor of a high rise in Singapore.
You could also go one step further and make a 6dB collinear like this from Neil Arundale (I have made and used one of these too and it compared equally with a £120 commercial collinear).
I hope that this inspires someone. If you get connected up please consider sharing your AIS data with us. We can provide a dedicated port and web view for your data.