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