Digital to Analogue Converter For A Terrestrial Cable Signal

Arduiners.....

I need a solution to my problem.

How would I go about turning the Digital signal for my cablebox to an analogue signal, then use a resistor and capacitor to create a time delay in the signal and then turn it back from an analogue signal into a digital signal to be received by my cablebox?

Or is there another way?

The goal here is to create a time delay without recording or duplicating the signal by means of slowing the signal down through a lagging process.

I know I can control the length of delay within the signal using the RC Time Constant but only on an analogue signal. But can that be implemanted using the Arduino, if it is at all possible that is...?

Any help would be greatly appreciated!

FYI, digital signal is much easier to delay, than analog. All you need is a memory bank, proportional to time delay x carrier freq. More spec. details of your signal, would help to answer if it's possible to do with arduino.

How many nanoseconds of delay did you want to add? DigiKey.com sells delay lines up to 10 nanoseconds.

I'm confused on why you want to do this in the first place.

The signal from your cable company is an analog signal that is modulated to provide digital communication. So you are suggesting to go from raw Analog, decode the modulation to get a digital stream, convert that to some intermediate analog signal, delay it with an overly simplified method, generate a digital stream from your delayed analog, and finally generate an analog signal modulated with the digital stream.

How many of those steps do you think you can do without introducing error?

I don't know the specifics of the signal apart from its digital and used for virgin cable tv. It uses a tris102a attenuator and with a 5 - 1000mz filter I think....

I've been trying to find out more information but its proving difficult!

seanlangford: I've been trying to find out more information but its proving difficult!

There's a reason for that. Partially because the specifics probably aren't published and partially because I don't think you realize what it is you are trying to find.

First you need to determine what the modulation being used. As I said, it is an analog signal that is being modulated to carry digital data. All digital communications is actually analog. http://en.wikipedia.org/wiki/QAM_(television)

Once you figure out what modulation is being used then you can start dealing with the digital protocol used for the actual data.

The hardware necessary to do what you are proposing is not exactly trivial.

[quote author=James C4S link=topic=88512.msg665216#msg665216 date=1327421972] I'm confused on why you want to do this in the first place.

The signal from your cable company is an analog signal that is modulated to provide digital communication. So you are suggesting to go from raw Analog, decode the modulation to get a digital stream, convert that to some intermediate analog signal, delay it with an overly simplified method, generate a digital stream from your delayed analog, and finally generate an analog signal modulated with the digital stream.

How many of those steps do you think you can do without introducing error? [/quote]

In the UK we have to pay tv licencing to watch tv as its brodcast. I just wonder how it would stand if I recieved the signal 30 mins or an hour later as there is no definition in the terms and conditions of what the time is "at broadcast". I assume that there would be reasonable terms as to general lag for a few milliseconds because of the speed at which the signal travels through the cable from the source to my reciever but no greater than expected

I enquired about the signal and was told that it was an 8 bit digital signal that carries HD tv....

But I still need to be sure.....

The projects a bit devious but I wonder if it can actually be done and got away with.

[quote author=James C4S link=topic=88512.msg665245#msg665245 date=1327423341]

seanlangford: I've been trying to find out more information but its proving difficult!

There's a reason for that. Partially because the specifics probably aren't published and partially because I don't think you realize what it is you are trying to find.

First you need to determine what the modulation being used. As I said, it is an analog signal that is being modulated to carry digital data. All digital communications is actually analog. http://en.wikipedia.org/wiki/QAM_(television)

Once you figure out what modulation is being used then you can start dealing with the digital protocol used for the actual data.

The hardware necessary to do what you are proposing is not exactly trivial. [/quote] I was not aware that the signal is an analogue signal modulation that carries the signal.... My idea of digital as to analogue is a series of on and offs as opposed to signal strength....

Maybe my question should be changed to whats the best way and easiest way of delaying the signal without recording it.....

seanlangford: The projects a bit devious

Sounds like someone is trying to beat someone else at Mastermind by sneaking early answers :D

A workable technique I've used to achieve a five-minute delay similar to what you want to do, although it involves a fair bit of complex electronics is:

  • Subscribe to V+ or TiVo
  • Install the V+ or TiVo box, or get Virgin to do that for you (that's the complex electronics, right there)
  • Start watching your channel
  • Press "pause"
  • Count 300,000 milliseconds or so
  • Press "play"

I just wonder how it would stand if I recieved the signal 30 mins or an hour later

Even if you could this, I'm sure the powers-that-be and their lawyers would say that in order to "delay" the broadcast you had to have received it "at broadcast".

I enquired about the signal and was told that it was an 8 bit digital signal that carries HD tv....

8-bit HD TV? Not a chance.

Pete

After my sarcastic reply, I thought I'd dig a bit myself to make up for it. I did find a bit of techie info over at CableForum, if it helps :)

seanlangford: I enquired about the signal and was told that it was an 8 bit digital signal that carries HD tv....

That's a pretty generic description, which really doesn't make much sense.

seanlangford: In the UK we have to pay tv licencing to watch tv as its brodcast. I just wonder how it would stand if I recieved the signal 30 mins or an hour later as there is no definition in the terms and conditions of what the time is "at broadcast".

I must be missing something obvious here. What difference would it make if you received the signal delayed by a few milliseconds (time of flight) or 30 minutes (physical delay)? You're still watching the signal as it is broadcasted. One method just has a larger buffer.

How would the provider know it was 30 minutes delayed and know not to charge you for it? In fact, wouldn't that raise a red flag that something is wrong between their transmitter and your receiver? This brings up another aspect to consider. Your signal is probably bi-directional, adding even more complexity.

I guess I don't see the connection between you delaying the signal and you not getting charged for it.

The goal here is to create a time delay without recording or duplicating the signal by means of slowing the signal down through a lagging process.

No you can't do it this way at all. I used to design digital set top boxes and your thinking is very mixed up. That is a complex digital signal and just adding a phase delay will not change anything at best and stop it working at worst.

In the UK we have to pay tv licencing to watch tv as its brodcast. I just wonder how it would stand if I recieved the signal 30 mins or an hour later as there is no definition in the terms and conditions of what the time is "at broadcast".

No, the TV license is not for "watching tv as its broadcast" it is for the installation of equipment capable of receiving a live TV transmission. The fact is that you will still be receiving it live, (that's how it enters you system) the fact that you just won't be watching it live which will not affect the license at all. That is why you had to have a license even if all you did was record signals onto a VCR to watch later, or use the Tivo solution above.

Currently there is a delay that can be up to 5 seconds between live reception on different platforms. Try having to Radio 5 live via medium wave, DAB and DTT. In fact I used to like to listen to the radio football cometary and watch it on the TV but now I can't because the radio is so much in advance of the TV that they comment on shots missing or scoring before the pictures even show the ball close to the goal. So you don't see TV live now anyway.

el_supremo: Even if you could this, I'm sure the powers-that-be and their lawyers would say that in order to "delay" the broadcast you had to have received it "at broadcast". 8-bit HD TV? Not a chance.

Pete

Well I can still recieve the broadcast but if I don't have a tv then I'm licence exempt even though I have the cable coming into my house that carries the signal.....

My information on HD tv and the bit rate is wrong then and I will have to have a look....

Is "license exempt" what people on the other side of the pond call "stealing?"

seanlangford: Well I can still recieve the broadcast but if I don't have a tv then I'm licence exempt even though I have the cable coming into my house that carries the signal.....

I don't think you're right about that. The license covers your use of 'receiving equipment' and goes on to define that and what you're allowed to do with it. It explicitly covers the use of recording equipment and I believe your proposed delay line would be classed as that. If you're hoping to weasel out of needing to pay for a license, I am reasonably confident that you aren't going to succeed.

Is "license exempt" what people on the other side of the pond call "stealing?"

Well it's a bit more that that it is tax evasion, punishable by a £1000 fine and confiscation of your TV equipment.

I don't think you're right about that. The license covers your use of 'receiving equipment' and goes on to define that and what you're allowed to do with it. It explicitly covers the use of recording equipment and I believe your proposed delay line would be classed as that. If you're hoping to weasel out of needing to pay for a license, I am reasonably confident that you aren't going to succeed. [/quote]

Hence the reason for using the RC Time Constant, but the DAC/ADC would need to use some sort of memory to convert the signal anyway which would include recording the signal to be processed....

I think I can be reasonably confident in my weaseling that as long as I don't use a tv to watch or record the signal that I don't need a tv licence...!

Ahem!

The law states that you need to be covered by a TV Licence if you watch or record television programmes, on any device, as they're being shown on TV. This includes TVs, computers, mobile phones, games consoles, digital boxes and Blu-ray/DVD/VHS recorders. You don't need a licence if you don't use any of these devices to watch or record television programmes as they're being shown on TV - for example, if you use your TV only to watch DVDs or play video games, or you only watch ‘catch up’ services like BBC iPlayer or 4oD.

seanlangford:
The law states that you need to be covered by a TV Licence if you watch or record television programmes, on any device, as they’re being shown on TV. This includes TVs, computers, mobile phones, games consoles, digital boxes and Blu-ray/DVD/VHS recorders.

Forget all of the technical hurdles, step back and realize that you are trying to build a device to bend legal terms. I have no idea how to build a circuit to do that.

I find it impossible to believe if you were caught using this device, the explanation “but it isn’t live! I DELAYED it!” would be accepted.

My lack of knowledge for your region makes it hard for me to understand at what point you stop paying. I assume you pay a fee to the provider. I’d really like to hear your explanation on why they shouldn’t be charging you anymore.

seanlangford: I think I can be reasonably confident in my weaseling that as long as I don't use a tv to watch or record the signal that I don't need a tv licence...!

I don't see any fundamental difference between recording the signal onto a VCR tape, or sending it through some other sort of RF delay system. Your recording device has received the signal and requires a license. Also note that you need a license to record the signal, even if you don't watch the recording subsequently. (I assume that you do plan to watch the delayed signal eventually, otherwise what would be the point? But even if you never actually watch it, you need a license in order to record it.)