Not all 11n devices support both 2.4GHz and 5GHz.
Contact Samsung to confirm if the wireless card in your smart TV support dual bands or not.

M Diamond wrote

Not all 11n devices support both 2.4GHz and 5GHz.
Contact Samsung to confirm if the wireless card in your smart TV support dual bands or not.

u mean i should disable 2..4ghz and try to use 5ghz only ?

Your laptop and samsung f6400 cannot detect 5GHz Wi-Fi, which may be limited by themselves.
If they don't support dual band but 2.4GHz only, they will not be able to detect 5GHz Wi-Fi.
Although they are 11N devices, it doesn't mean that their wireless cards support both 2.4GHz and 5GHz. Nothing to do that the router.
Is that clearly enough?

dejavu wrote

u mean i should disable 2..4ghz and try to use 5ghz only ?

Your Samsung TV do not support 5GHz. So they cannot detect the 5GHz Wi-Fi.

Your laptop may probably not support 5GHz either. Better check that from the laptop's support.