[ale] Wandering OT: Re: Car PC's and internet radio?

[Sean Kilpatrick]

On Tuesday 17 April 2007 23:09, Jeff Hubbs questioned an assertion by Dale
Heatherington that satellite radio is one way only:

| Do you know this as fact, or are you presuming it? ?Can you point me to
| a specification or, better yet, otherwise demonstrate that it's
| downlink-only?


Jeff,
I am not a ham or any other sort of "expert" in radio. But I do know a
little bit about the subject.
Consider your cell phone and its battery. It can transmit a high frequency
signal only a few miles at most to reach the nearest cell tower.  If you 
wanted to use your cell phone on a boat cruising along the coast, you would
need a signal amplifier and a much better and taller antenna.  West Marine
probably can sell you the kit, but it aint cheap.
For a satellite radio receiver to also transmit a signal back to the bird
22k miles above you would need a lot more transmit power than your cell
phone has and a much better antenna, which would (for your own safety) have
to be mounted _outside_ the car.
By comparison, satellite telephone service uses far more complex satellites
(much more expensive to build and operate) and the rates reflect the
differences. And I believe that the satellites providing this service are
like the GPS birds -- maybe 150 miles above the surface -- which means a
hellava lot less transmit power is needed to reach them.
Yes, a minimal cell phone could be built in to an XM radio and could easily
phone home data, but I assure the cell phone network(s) would want a piece
of the action, and they aren't about to provide that service for pennies a
month.
The bottom line is that a combo receive/transmit radio is going to cost a
lot more money than one that only receives. A radio transmitter that
can reach an orbiting satellite is going to have to be bigger than an ipod,
Star Trek notwithstanding, and its going to need an external antenna.

All sorts of computer software "phones home" using the internet and we have
gotten used to worrying about exactly which data is being sent where. But
Satellite radio isn't (yet) capable of doing that. 

Sean

-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: not available