Looks like they opted for the Lotus Elise hardtop rather than the Roadster top too!
Err, that would be me !
I specifically wanted to improve the FM radio reception as the stock aerial is next to useless, but do it without drilling holes in the existing bodywork. I also didn't like the appearance of the stock Tesla solid roof and wanted to keep the car looking low and sleek. Plus the Kevlar version is nearly £5k here in the UK ..
One reason why FM is so bad is because the car body is carbon fiber and not metal which on most cars acts as the essential "ground-plane" side of the antenna - something that seems to have been overlooked by Tesla / Lotus engineers! Another reason is the electrical noise emanating from the cars electronics, but this is reasonably well contained.
Ideally a single wire aerial should be about 85cm long to act as a quarter wave monopole antenna for FM frqs of 85-100Mhz. I made up an 85cm one to test and it works exceptionally well when vertical, but obviously it looks odd on such a small car whether vertical or tilted over at 45' or more. So I fitted a 1/8th wavelength instead. This works almost as well and is fine with moderately strong stations but really needs a balun coil at the base to improve it a bit more. Tilting is a compromise which gets worse the further over you go.
In order to improve the signal reception with the 1/8th wavelength aerial, I needed to fit a ground plane at the base of the aerial to make it more like a 1/4 wavelength dipole antenna. To do this I bought an Elise double-skinned roof from ebay, repainted it to match the bodywork, added two layers of sound absorbing material and put a copper mesh ground plane sandwiched in between and connected to one side of the FM aerial feed. I used a fine grade mesh covering an area of about 0.7m2, the bigger the better.
I've now got *significantly* improved FM reception and the car is noticeably quieter at highway speeds of 70-90mph and I'm very happy with the result. Total cost of everything was under £500.
(Mods:- This ought to be split out into separate thread for improving Radio reception and / or fitting Elise hard top .. )
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