pctv nano stick only works for a few minutes, why?

Sounds like you need to talk to PCTV Systems.

If you look at the minimum system requirements, it is a Windows only product, as you posted above. It evidently isn't supported on a Mac, which is what may be causing your problem.

http://www.pctvsystems.com/Products/ProductsEuropeAsia/Digitalproducts/PCTVnanoS tick/tabid/167/language/en-GB/Default.aspx

Well, their (North American, anyway) webpage indicates that they are selling a PCTV for Mac with Elgato EyeTV software: http://www.pctvsystems.com/Products/ProductsNorthAmerica/MacproductsUSA/PCTVforM acHDminiStick/tabid/175/language/en-US/Default.aspx.

So I would expect that they support any product that they sell (and you should hold them to this). But mainly, the description you are giving sounds like a HW issue with the tuner stick...unless there are some logs from the EyeTV software indicating some other issue - you confirmed the antenna works and if the problem was with the USB port there would likely be other issues.

Therefore, if the tuner is dropping the signal, it suggests the tuner is faulty. Which is, again, a PCTV Systems problem.

However, if you bought a Windows-only product from tehm...then all bets are off (but you could see if they will exchange for the correct product).

As Eric Root suggests, the PCTV nanostick may be Windows exclusive. On the other hand, "not supported" is not necessarily "won't work" and the fact that you have managed to get it working, albeit for only a few minutes, suggests that it might be worth persevering a bit more. I presume that your nanostick, like most USB TV tuners, uses a small adapter to step down from the standard aerial plug to a tiny socket on the stick. In my experience, these adapters make for a very touchy connection that easily comes loose. Once you have started up the program, try wiggling this adapter to make sure that is is making a sound and secure connection. If you get the "no signal" message almost immediately, then the connection may be the cause of your problem.

Make sure that your EYeTV Lite is up to date - an update to EyeTV was issued a day or two ago so EyETv Lite might also have one. Incidentally, you say that EyeTV Lite came with the nanostick so I am surprised that, if it was for Windows, it installed on OSX. If it is an OSX version, then it suggests that the nanostick should work on your iMac.

As far as I know, the only OSX specific USB TV tuner is the Elgato EyeTV DTT. They are not cheap compared with most USB TV tuners but you can find them on Ebay for a lot less than the retail price and they DO work on OSX.