I purchased this from Amazon in the hope of improving my new christmas prezzy Navman s50 3d, looks neat on picture but they don't show the ariel wire that comes with it to make it work. Its a wire in plasic with 2 suckers to fix it to the inside of the windscreen and jack plug that goes in the base of the T" TMC unit. It is very poor it gets in your line of vision, the suckers plink off when driving, and to top it the signal pick up which is from Classic fm is poor every where unless as stated above you are on top of the transmitter. Navman bless them tried to help and even sent me a full replacement after asking all the right questions...was it plugged in..what roads. The replacement worked better but still rubbish in Liverpool City centre and best on areas of M57 and M53 but quickly lost. So answer...Navman say they dont make ext aerials which they should as it works. I found a web forum which sets it out, got to Maplin Electronic buy the Mini scan aerial which picks up 101.1 mz; then you will need a few adaptors to go from BNC to Stereo 3.5mm jack (via Phono) which I did with a 90 degree phono to make it fit under unit. The neat 12" aerial has 3m of cable and a neat little mag mount so it just sticks to the roof (does at leat 70 mph...faster is illegal!).
Now I pick up a signal almost anywhere in Liverpool and Wirral on ordinary roads, why Navman don't make one is a mystery but this works and its neat and simple. The lot cost me a total of £22 odd and now gives me a fully functional TMC unit just a pity Navman are so dim on this as they big up the system but fail to deliver.