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Circuit for detect if the video signal is inverted ? HELP ME

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Jan 25, 2002
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cablecrypt circuit


I have a cable analog decoder called CableCrypt , The encryption scheme is encrypt the video (by removing HV syncs and randomly invert the video signal) and encrypt the audio signal digitally.

I cracked the video signal but there is the problem of that the picture is randomly inverted ,
I am searching for a circuit that can detect if the video signal is inverted or not .
EX. If the video signal is inverted ,The output is HIGH (+5V) ,If it is not the output is LOW (0V).


Please don't reply unless you have useful information to add on this post.Thanks


Thanks for the link. But i visit it a long time ago. My system is deferent , The link for the US and CANADA systems.


Dear friend:
Regarding your question:
1- Normally this kind of scramble send the key to invert-noninverter video frequency madulated onto the video carrier. So you have to watch the carrier using a spectrum analyzer to check if the video carrier has some FM deviation.

2- One question: Is the switched video clamped to some constant DC level?



The encryption system is simply removes all The horizonyal and vertical syncs from the video signal, then add the data packets (command packets) in the VBI part of the video signal.
The audio is digitized and encrypted and put it in the the horizontal sync place.

The invertnoinvert exist in the data packets send in the VBI part.
But i search for a general and simple circuit that i can detect the status of the incoming video if it's inverted or not .
in other words how can i if any video signal is inverted or not ?
So i can modify it to work wtih my decoder.


dear friend ihave try very much with cablecrypt decoder and the inverted video.
fortunatly there is not a 100% solve for this.
the best i do was to rectify the video signal
with an operation amplifier.
when the video was inverted the voltage was
a litle more than normal video.
with a smithtrigger adjustable and a flip-flop i take this voltage.
the result was a 90% correct.
i beleive to help you a litle.

Not knowing too much about your video crypto system, but: In PAL video signals there is a colour burst signal just after the line syncronizing signal. It contains about a dozen periods of a colour reference signal of 4.43 MHz. A crystal-based VCO oscillator of 4.43 MHz is locked onto that burst. In case the signal (including the colour burst) is inverted then the phase of the colour burst would also be inverted. A detecting circuit based on a PLL and sensing that colour burst phase change, could it be an idea?


Zerc, Can you send to me a diagram for your circuit (I May modify it to get 100% results) ?
do you know any soultion for the audio hack ?

Thanks Again or all other replies,

Dear friends:
1- The randomic nature of the video in the time domain;
2- The video sinal with inverting non-inverting lines is clamped at the same DC level,
I'm pretty sure to be virtualy impossible, in time domain, recognize if the video signal itself was or not inverted.
To build a circuit based on APL changing of the video is a total waste of time, once this APL's changing will be senssible (to triger a voltage comparator) after several video lines had gone.
Also try to do something in the color channel wouldn't carry us anywhere, once this channel uses AMDSB-SC.
As the burst signal in this kind of encoder is kept unchanged, it wouldn't be useful.
Listen to me, the only way to have the video with the right polarity is to find out the key signal anywhere inside the baseband.
Sorry, but regarding a lot of experience I have had in this kind of anolog encoder, I'm pretty sure about what I'm saying.


the best way to do what you need too do

is to use a pic micro

like everyone does in the uk

it can perform filter equassions

and decrypt on the fly

the audio is easy to decode

the video can be tricky

but if you need to do it
make a working ttl or cmos equivelent

then draw it up as a model

model it
turn the model to code
and cut the size down to one pic 84

here we use
also "fold over encrytion algurithm"
or foea for short
as this is the corect definition to your type of encryption

i have a number of designs for cable decoders

but only analogue systems

not full digital ones

digital systems are very hard to decode efficiently
without a 586 at least driving them at 115 kbps

so best of luck

ill dump the designs in a zip

we are the borg folder in fm1


<font size=-1>[ This Message was edited by: THE BORG on 2002-02-02 02:14 ]</font>

Dear Borg:
With the due respect, I'm eager to know what are you talking about if that means to indentify the polarity of the video signal without recovering of the key signal was used in the encoding process. So please, post your design as soon as you can!!!


dear friends hi
nandopg has right. iremember that the diferrence was only 1mv but with a good op amp.can take the output you want.
the circuit works perfect in the most movies
but not to the football where there is no diference in the rectifing voltage.
if i found the circuit i will give you

I have simple idea. If you invert signal you just have to decide wich one is positive. Positive signal will have the same polarity of sync as 64us ago. For this you can use S/H, comparator simple logic and analog multiplexor.

ok below youll find a collection of pictures {the schematics are in the zips}

im not saying yes it will definatly work

but it uses the same principle and im shure these may help you

a little
nando pg
our analogue system here is the same kind of thing

you are basicaly filtering the signals in the correct order with the pic
adding them together in the correct order and inpuiting them

there are several examples there

of different approch

all use a 508 509 or pic 84 one uses a 74

[ This Message was edited by: THE BORG on 2002-02-03 01:41 ]

[ This Message was edited by: THE BORG on 2002-02-03 01:45 ]
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here it is

Uploaded file: **broken link removed**
Last edited by a moderator:

Dear Borg:
I skimmed all files inside the exe you uploaded, but I couldn't find anyone that help us to solve the random video inversion problem without recovering the key signal. Could you indicate me the specific files that have this information?


The files are a modchip codes for the SA and JERROLD decoders used in USA,CANADA and UK (I think) not for cablecryptcomcrypt.

I agree with nandopg that there is no any files about how solve the random video inversion problem without recovering the key signal


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