But suppose you put your radio in a shielded box, stop paying, wait a
> few months until they give up trying to deauthorize you, then bring it
> back out -- are you still authorized? Or does every authorized radio
> have to get reauthorized at some periodic interval?
I'm not sure about XM or Sirus, but typically the transmitters will occasionally resend deauthorization lists out randomly to catch people that try to do what you described. It takes very little bandwidth to send out unsubscribe commands, so there is no reason that they couldn't dedicate one entire music channel's worth of bandwidth to running the list over and over until the end of time.
Bottom line: Do individual radios actually talk back to the satellites
> at any point? Or do authorization and other command signals flow only
> from the satellites to the radio?
In the case of radios all transmission is from the satellite to the radio there is no feedback or return signal possible.
TELECOM Digest Editor noted in response:
My understanding is satellite receiving units do not 'talk back' to
> the satellite; everything is done from the satellite end, and as long
> as there is any 'unfinished business' with any one receiver, the
> satellite company just keeps on sending over and over the required
> codes. DISH has those little plastic 'smart cards' which have to
> be replaced once a year or so, so I assume if you were not paying, at
> best, you'd get the remainder of the time available before the Smart
> Card ran out. I do not know what some of the others are doing. PAT]
DISH (and similar) do not need card swaps once a year or anything of the sort, a new card is only needed when the encryption technology changes. They're currently in the middle of changing from NAGRA1 to NAGRA2. NAGRA1 did not deactivate cards by time, only by explicit command from the broadcaster.
NAGRA2 has a timeout built into the algorithm so that you can't just pull the card after you deactivate and still expect to get channels.