TELECOM Digest OnLine - Sorted: Re: Satellite Radio Authorization: How Does it Work?

Re: Satellite Radio Authorization: How Does it Work?

Isaiah Beard (
Sat, 12 Feb 2005 00:29:44 -0500

AES wrote:

> Pointers to info on how XM and Sirius systems work, specifically as
> regards authorization?

> When a satellite authorizes a given radio, does it do it by sending
> that radio (and, as a side effect, all other radios) some kind of
> digital key that combines with some unique built-in matching key in
> that particular radio to enable it to decode the broadcast content?

To an extent, yes, this is how it works. A "hit" code is sent from the
satellites and is broadcast over the "preview" channel, which the
radio must be tuned to and must receive the full key before the radio
can decode the whole signal and the remaining channels are "unlocked."
Activation keys generally take about 10-15 minutes to compeltely
download, and the key is transmitted six or seven times in succession
so that your radio has a chance to get a clean copy (meaning the
activation code persists for about an hour). If you don't have your
radio on during this period, a "refresh" signal can be sent later,
when the radio is ready.

> If so, presumably if you stop paying your bill it can also deauthorize
> your radio by sending something to wipe out the code?

That's one way to do it, and if one had their radio turned on while
the deactivation code was being sent (the duration tends to be around
48 hours if activation traffic is very high; if not, then the code
persists for longer), the radio would shut off more quickly than it
would the "other" way (which I will describe shortly).

> 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?

If you do this, and you turn your radio on, then your radio will stay in
an 'activated" mode for about an hour or so. However, the key that's
stored in the radio has already expired, so it is actively looking for a
renewal code. If it doesn't get one, the radio "shuts off," going only
to the preview channel.

> 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?

It's only one way, from satellite to receiver. No information is uplinked.

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