Physics question (for Dan?)

[Steven G]

I have wondered about this for a while.

I know some people have satellite tv service in their homes. Their satellite dish has to be aimed perfectly for them to get reception on their television.

I personally have satellite radio in my car. Naturally my car is in motion most of the time I am listening to my radio.

My question is why does my satellite radio antenna not have to be aimed in an exact way as the satellite tv dish antennas have to?

 

[Otis]

Dan will let us know how wrong I am.

I'd say it's because the signal for your radio service is sent by many satellites simultaneously (located in various positions in the sky), whereas the TV signal is sent by a single satellite (always positioned at the same location in the sky, relative to the house).

If that idea fails, then my backup plan has to do with differing frequencies, wavelengths and/or amplitudes.

 

[topsquark]

What is this? Pick on Dan day?

The more information you need to process a signal the more you need something to focus a signal for you. (To get a bigger Q factor.) For example if you are listening to music on the radio you don't really need much of an antenna. Cue the old car radio antenna that were simply a coil of wire pointing straight up. If you wanted an expensive one they came in several such coils. Roughly speaking the longer the wire the more of the wave they could catch.

Sirius radio needs a bit more but as Otis suggested the antenna are picking up waves from multiple sources. I'm not up on the Engineering of it but they can now embed the antenna on the top of the windshield that isn't normally used. It seems the antenna here is made up of a layer or perhaps layers of some kind of metallic paste.

And, of course, if you need everything you can get out of it such as Pay Per View on your TV then you need something to focus the signal to pick up on just about everything. Hence the dish pointing at the satellite sending out the signal.

-Dan