To my understanding, premium cable channels in analog cable systems are blocked by filters attached in a cable box near a person’s house, which block out the band that particular channel is transmitted on. When you order such a channel, a cable guy comes out and yanks that filter.
Given that, how can those channels offer a free weekend? Obviously, no one is going house to house to remove the filters…
One might guess that they encrypt the signal, and the filters unencrypt it, so they just turn off the encryption for the weekend, but this is unlikely since the filters aren’t that complex. I’m guessing they just block out X-Y bandwidth range, which covers whatever channel the premium service might be on.
In most areas, the filter system is no longer used for premium channels, and hasn’t been for a while. Premium channels are blocked by scrambling the signal such that your normal TV can nol longer recognize it - usually by messing with the sync pulses that tell the TV where each line of video begins and ends. Embedded signals from the cable company tell each cable box what channels it is and isn’t allowed to descramble.
To give free weekends, the cable company either turns off the scrambling for the channel, or sends a signal to your cable box telling it to descramble those channels for a certain period of time.
The key piece of equipment here is an “addressable cable box”, which means that the cable company can talk to each box individually. This is required to do pay-per-view (since that’s turning off the encryption for one person only). Since pay-per-view is both lucrative and popular, most cable boxes nowadays are addressable.
So essentially the filter can be removed from the central office. No need to make a house call.
Cable boxes these days are pretty much little computers. Each one has a unique address, and every box gets a signal from the central office telling it what it can and can’t display. As said above, for free weekends all they do is unscramble the channel(s) at the central office, no filter-removal necessary.
Note that there are still ways to play with this system. For example, one friend of mine who works for the cable company told me a few years ago that you can watch pay-per-view at a friend’s house if he has basic cable but no cable box. To do this, you call the pay-per-view order number. Your box will receive a signal that unlocks the particular pay-per-view channel you requested at the appropriate time. Now, after your box is unlocked, you can disconnect it, take it over to your buddy’s house, hook it up, and watch the movie on his big screen TV.
Today, in the era of digital cable, that trick probably wouldn’t work anymore; today’s cable boxes are about a keyboard away from being full-fledged computers.
Also note that on most modern cable systems, even analog systems, you can’t receive any premium channels without a cable box (an addressable one, at that).
But what about slobs like me who don’t have cable boxes (they’re part of the vast alien conspiracy you know), and still get to take part in free booby, er, movie weekends? I have to think the signal is getting de-fritzified at the home office.
Strange. Well, the experience I have was at my friend’s house when we were looking for a break somewhere when his cable wasn’t working right… they still had physical cable filters on their line color coded for different channels.
I don’t know whether he got free weekends, or not, but they’ve been doing this sort of thing for a long time, so I have to assume that there’s some way of getting past the physical filters.
Usually the premium channel will be put on some other channel that is not filtered out for those free previews. That way, people without an addressable box can tune in and watch the premium channel’s content. If you then wanted to subscribe to that channel they’d either remove the line filter or (in the case of scrambled analog) give you a box to descramble it. Or if you gave them a lot of $$$ they would give you a digital cable box.