Satellite TV or direct broadcast?
If you want satellite TV- Dish or Direct, you will need a satellite antenna. Full motion marine units are made by KVH and Raymarine. I have a KVH unit and it was installed in 2003 when we commissioned our 356. You will also need a satellite receiver box just like you have at home, furnished by your satellite provider. The antenna has to be mounted somewhere, usually on a pole, so you will need to purchase and install one. From the antenna come the leads to the satellite box. My unit has 2 leads for 2 tv's should you want them. The antenna is dc powered, but needs to be cleanly regulated power without fluctuations, particularly low voltage (even momentarily below 10.8v) or your card programming will be deleted. I have a transformer that converts 120v to 12v to supply the antenna. I use either shore, generator, or inverter power to power it. You will also need 120v power to the satellite box and the tv.
Initially, I had several instances of low voltage that wiped out the programming on the antenna card before putting the unit on the regulated 12v power supply. Since then, I have only had one outage and that was due to a malfunction of the satellite box that sent too high voltage back to the antenna.
I have had great success with the signal. The antenna is constantly trying to improve the signal, so you can have a much better signal than most people have at home. In choppy seas, it will break lock, but it will find the signal relatively quick. Sometimes in a tight circle, it will also break lock, but also quickly finds the signal.
If you are cruising, you need to set it up with the provider as a mobile unit like an RV. Your local channels won't follow you everywhere you go, but you can change locations by phone and get the local channels wherever you happen to be.
For internet, I use a verizon card and subscription as well as the local wireless in our marina. I have found verizon service most places we go. Portions of the Tenn-Tom waterway were without service two years ago and may have been more fully covered since I went down there. You will only receive signals near shore in coastal areas.
For offshore, I use Globalstar to get grib weather files and e-mail. The last couple of years, Globalstar has been unreliable. They claim to be launching satellites this fall that should make their system workable again. When it works, it is very slow, but does provide basic connection. I think there are some booster programs that work to make it somewhat faster than when I have used it but I have not tried and don't plan to until their system is back up to normal.
There are very expensive systems for internet if you have deep pockets and want service in very remote or offshore.
Someone else can comment on direct broadcast tv - I have never used it.