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The above is from a website linked in a piece of spam email I recently received. Now, normally I don't read spam, but when I saw an ad for a "Digital Power Filter" to get free PPV channels, I just had to check it out. The website for the ad mentioned above is: http://arbeo.fortherest.info/amite/cable, if you wish to check it out. Yes, they are selling 60 MHz High Pass Filters (HPF) for $39.95. A savings of $60.00! Man, I'm in the wrong business...
The idea on these filters is to block the two-way communication between the cable box and the cable company's billing computers. The cable TV system is Frequency Division Multiplexed (FDM). This means that each communication channel (TV channel in this case) is at a different frequency. Frequencies between 60 and 800 MHz on a typical cable TV system are reserved for the normal channels we watch daily. Below about 60 MHz, is where the two-way (data) traffic is located. This is where the cable TV company "talks" to your cable box, where "digital" TV is transmitted, and yes, where cable modem traffic is located. The idea is that on some cable systems, if you block the cable boxes' downstream data, you can order pay-per-view channels and not be billed. This is because the internal "descrambler" of the cable box is activated locally, but the cable box can't send the billing information back to the cable company. Of course, not all cable systems are alike, some even have the two-way communication frequencies operating up to around 120 MHz. Some cable boxes will only "descramble" the signal after a two-way handshake (with the billing system) is established, rendering these filters useless.
A legitimate use for these filters is to remove TV interference caused by TV broadcast, citizens band, or amateur radio transmitters.
Schematics
All capacitors in picofarads, inductors in nanohenrys. Filters are 5th order Chebyshev.
The filter connects in-between the incoming coaxial cable (wall) and the cable box. Use only one of the three filters shown.
This filter only works on analog Pay-Per-View cable systems where the scrambled channel is transmitted on a standard cable TV frequency and the cable box has the ability to internally descramble the signal (i.e., most older systems).

Stopband : 65 dB minimum at 10 MHz Cutoff : 1.0 dB at 30 MHz

Stopband : 30 dB minimum at 40 MHz Cutoff : 1.0 dB at 60 MHz

Stopband : 15 dB minimum at 100 MHz Cutoff : 1.0 dB at 120 MHz