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Cable hacking
Notch Filters Made Easy by: Mad Scientist Labs, Inc.
Revised: 9/17/93
MATERIALS REQUIRED:
1 - Radio Shack mini-box ( #270-235)
Note: These little boxes USED to be made out of conductive metal,
kinda like tin, they were perfect, Radio Shack changed the box
to a aluminum type box. Not really that conductive. So, make sure
you add a ground wire to the Coax connectors in the box.
1 - 1/4 watt resistor, 2.2k-2.4k ohm
(RS #271-1325)
1 - 75pf-100pf variable capacitor
Special Note: These babies are hard to get, they are mostly
mail order capacitors, mainly due to the fact that they are
variable. San Mateo Electronics does have a small supply, but
not in this range.
(A.C.E. Electronics in Sunnyvale off of Laurance Expressway has
a supply of Variable Capacitors in the 15pf-90pf range for
$2.00 a pop. If your nice to the guy, he will sometimes charge
you only .50 cents each.)
2 - F61a chassis-type coaxial connectors (RS #278-212)
13" - No. 12 solid copper wire
12" - RG59 coaxial cable
Chassis-Type
Coaxial Connectors
RS #278-212
[ ] [ ]
-|--------------------[|]------[|]
| | |
| | |
| |_/\ /\ /\ /\ /\_|
| \/ \/ |\ / \/
| 2.4k Ohm | Coil from
|-----------\/\/\/\/-------| #12 AWG Solid Copper Wire
| Resistor |
|---------| (1/4 Watt) |
| | |
__|__ | [-|-] 25pf-75pf
___ | {-|-} Variable Capacitor
_ |----------------| (Note: 15pf-90pf Variable
Ground Capacitor will do also)
DIRECTIONS FOR BUILDING A HOME NOTCH FILTER: Works on HBO, SHOWTIME, Etc.
1. Bare a length of No. 12 gauge solid copper wire and twist around a 3/8"
nail or rod to form a coil of 9 turns. Elongate coil to a length of 1 1/2"
inches and form right angle bends on each end.
2. Solder the varible capacitor to the coil. It doesn't matter where you
solder it, it still does the same job. The best place for it is in the center
with the adjustment screw facing upward. Solder the other free end to ground.
Note: When it comes time to place coil in box, the coil must be
insulated from grounding. This can be done by crazy-glueing a piece
of rubber to the bottom of the box, and securing the coil to it.
3. Tap coil at points 2 1/2 turns from ends of coil and solder to coaxial
chassis connectors, bringing tap leads through holes in chassis box. Use as
little wire as possible.
4. Solder resistor to center of coil and ground other end of resistor to
chassis box, using solder lug and small screw. If you are using a aluminum box
from Radio Shack, make sure this resistor is grounded to the side of the
coaxial connectors.
5. Drill a 1/2" diameter hold in mini-box cover to permit adjustment of the
variable capacitor from the outside. Inspect the device for defects in
workmanship and place cover on mini-box. Tighten securely.
6. Place device in line with existing cable on either side of the coverter
box and connect to television set with the short piece of RG59 coaxial cable.
Set television set to HBO channel.
7. Using a plastic screwdriver (non-metalic) adjust the varible capacitor until
picture tunes in. Sit back, relax, and enjoy!!!
Note: The reason you use a NON-METALIC screwdriver, is so you don't short
anything. So, PLEASE PLEASE PLEASE, remember, use a NON-METALIC
screwdriver for this final stage.
For those of you that really really need to know more about WHY you are
building a NOTCH Filter, read on below.
CABLE TV SCRAMBLING TECHNIQUES by Mad Scientist Labs, Inc.
-----------------------------------------------------------------------------
There are 4 major methods of pay-channel security and each has different
consequences for cable ready receivers. The 4 systems are jamming, trapping
out-of-band scrambling and in-band scrambling.
Jamming:
A jamming signal is placed between the picture carrier and and the aural
carrier of the secured channels. The cable operator supplies a filter for each
customer for each paid channel. This type of security is easily defeated by
homemade notch filters.
Trapping:
In these systems frequency filters are installed in line with the cable drops
on telephone poles. The traps are removed for customers paying for the premium
channels. Cable-ready TV's work fine in these systems.
Scrambling - The gated Sync Methods:
Scrambling in the cable TV business still generaly means pulsed sync
suppression. In its simplist form, amplitude of the picture carrier is reduced
by 6 db during the horizontal blanking intervals and sometimes during the
vertical blanking intervals. The resulting video signal has sync tips between
the black and white levels. Sync seperators in the set cannot operate properly
with this signal, nor can AGC and color circuts, so the picture is scrambled.
The decoder compensates by antennuating the signal during the time in which the
transmited signal was not antennuated. In order to accomplish this, the logic
controlled gain switch must get timing information. In-band systems transmit
pulses as amplitude modulation of aural carrier or a seperate carrier in out of
band systems.
Out of band scrambling:
The usual setup is that the decoder is connected directly to the cable
ahead of the channel converter. Decoding is done at the pay channel frequency.
The decoder is likely to be in a seperate box, added to an old system to provide
pay channels. The box consists of a simple receiver (90-120mhz) for the
out-of-band data carrier and a broad band 6db gain switch. There is provision
for several scrambled channels, each which has a different data carrier.
This system is directly compatable with cable ready receivers. Without the cable
converter, the decoder is connected to the TV. Tuning and remote features of the
TV are preserved with the only inconvience being the need to operate the switch
on the decoder when changing to and from any scrambled channel. Out-of-band
systems tend to last until the operators using them rebuild to provide for a
large increase in the number of channels.
In Band Scrambling:
In this system any number of the available channels can be scrambled.
Because the data carrier for each scrambled channel is its own aural carrier,
only one data receiver, at the aural carrier frequency (eg. ch 3) is required.
The decoder detects the presence or absense of data automaticly switching itself
in or out. The converter-decoder box can be hardwired to decode just the
channels ordered, using a prom like device. Alternatively, the transmitted
channels can be "tagged" by time division multiplexing binary tag (program
identification) data with the sync data on the aural carrier. The decoder boxes
can be wired for "tiers" (groups of programs the cable operator sells together)
rather than fixed channels, giving the operator more flexibility.
The decoder boxes can be "addressable". These boxes have a seperate out of band
data channel for data from the head end. Each box has a serial number burned
into its logic or otherwise available to its logic circutry, and its channel or
tier authorization stored in volatile ram. A computer at the headend periodicaly
addresses all decoders in the system individualy and loads each with the channel
or tier capacity ordered by the customer. The need for house calls is reduced,
PPV (Pay per view) is possible, and missing boxes cam be turned off, rendering
them useless for premium channel viewing. Some but not all of these features can
be programmed into out-of-band systems.
Aside form their ability to generate sync pulses, thus foiling the scrambling
system, cable ready TV's have presented another difficult problem for in-band
systems. Because the decoder operates at the converted channel, a channel
converter is required ahead of it. Whether the TV receiver is cable-ready or
not, it operates only at the converted channel, wasting the tuning and remote
control features.
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