Technical Question About Cable TV

[HandyMac]

I have cable TV, telephone and Internet here. All working perfectly.

I also suck the terrestial channels off the incoming NTL TV feed, so that I can watch bbc/itv without going thru the pace box - I can watch TV either thru the pace box or the terrestial feed no problem. That arrangement works fine too.

I have put a splitter on the incoming feed to the TV, and run the terrestial signal off to another TV. Works perfectly.

Here's my problem...

What I want to do is split the signal again so as to provide the terrestial feed into my PC TV card. There shouldn't be any reason why that won't work. However the TV and PC are on opposite sides of the house (the PC is in my study). So to make this happen I would have to run a TV cable across the house from the TV to the PC.

The TV is fed from a 2nd wallbox immediately behind the TV.

As it happens the PC Internet feed has its own identical wallbox within 24in of the PC.

What would truly be wonderful would be if I could take the TV signal off that wallbox and stuff it into the PC TV card. Easy peasy lemon squeezy to run that short piece of cable.

Tried splitting the cable modem feed which comes off the PC wallbox, but it appeared to drop the signal to the cable modem (didn't bother seeing if the TV signal was okay, the PC has to have its Internet feed). So that doesn't look like a runner (presumably the cable modem is running a different set of frequencies to the TV?).

So my question is, is it likely that the wallbox in my study has the necessary TV signal on its output ports? If so then with the right cable surely I could pick off that signal to feed the TV card in my PC?

The wallboxes on either side of the house are identical. Both have 2 F-type sockets on the bottom. I had assumed that both would be carrying the same signals into the house and it is the box that is connected to the wallbox that picks off the right signals.

And what are the 2 sockets on these wallboxes? There is only 1 cable plugged into either wallbox. Are these sockets paralleled up? Just maybe I could try hooking the PC TV signal from the 2nd socket on the wallbox, leaving the Internet socket alone?

I'm obviously stuffed if NTL configure different signals to different boxes. That sounds a bit unlikely to be honest, but it could be the way it is set up. I just don't know what is on the NTL side of the box.

(BTW, I'm a qualified electronics engineer so a technology explanation wouldn't fall on deaf ears - you probably don't have to spell answers out in braille!).

Thanks in anticipation.

A

The modem signal is mixed in amongst the frequencies used for the analogue and digital signals. So the signal will be available on both wall sockets.
The trouble with splitting a signal is the two resultant signals are now at half the level of the original. The STB has a window of approx 10dBmV, not sure about the modem but its likely roughly the same. So it would depend upon the level available at the wall socket output, as to whether splitting it (and hence losing 3dB) the level is still sufficent.
Additionally connecting your TV directly to the cable feed may mean you are sending noise back out into the local network. The frequency of the noise will depend on the analogue TV signal your TV is tuned to, and changes as you change channels.

[popper]

to tell the truth, your probably asking for trouble spitting again as thats going to drop your levels even more, and its not like you can get a cable signal booster down your local DIY (shame that), your far better off getting yourself a DVB-T USB card (with BDA drivers) and setting up a good external tv arial too that DVB.

far easyer and you get the advantage of being able to stuff that DVB direct digital .ts feed through your lan (works nice over wireless 11g,see http://jtvlan.netsons.org/howto.php) to the other machines or special mpeg2 boxs.

[Stu038]

The same broadcast signals are everywhere on the network so in in theory you can split and split to your hearts content. The problem is that every time you fit a splitter you insert aprox 3.5dBmV of loss onto that feed.

From what your saying the feed that you've got into your modem has already been split elsewhere so is border line. There's nothing that you can do about that, though a service tech should be able to increase the levels into the property and reset everything.

The additional F connectors that are sticking out of the wall box are most likely filtered just to allow FM frequencies out for FM hook ups. There was a short period of time though when some areas deployed a splitter with a data leg which connected upto the modem while the other provided all the TV frequencies so you could try connecting your TV card to that.

Thing to watch for is that any messing about you do with cableing and plugging additional equipment in can not only affect your service elsewhere in the house but also the service of your neighbours, all of which could end up being billable back to you if the problems are proven to relate back to "unofficial" work that you've carried out.

[popper]

you could also get yourself a DVB-C (cable) card for your first split cable and use the direct .ts cable feed instead, but it seems you cant get a DVB-C with CAM that allows you to just plug in your payed for NTL smart-card and have it unscramble your NTL channels , shame that.

for now, mpeg2 will do, but in the near future its going to be AVC/H.264 encoding/decoding with everything,
the biggest problem right now seems to be the Hardware makers unwillingness to put a simple powerful and cheap FPGA re-programable chip on all their kit (along with a S-video in)so they/you could just write/port a working AVC/H.264 encoder/decoder and stuff anything through that unit to IP stream in AVC, so saving massive bandwidth.

perhaps your able to produce something and put a box/USB stick together and we might even be able to watch the avc HD decoded through that without messing with powerful CPU's/GPU's and expensive AVC/H.264 STB's just to watch the BBC HD

I watched it at work, far cheaper with other peoples equipment!

[popper]

well , what do you know, you could get these in 2004, shame your local computer shop still doesnt have anything like them ?, they come in a DVB-T form to (no AVC/H.264 though)
http://www.trimedia.co.uk/product.asp?id=202
"
H.264 MP@L3 D1 resolution up to 2Mb/s
MPEG-2 MP@L3 D1 resolution up to 10Mb/s
Supported by Trimedia Middleware and Conditional Access
Flexible audio and video output via cable options
USB 2.0"
the The Net100 at the bottom of the page is rather nice
as it means you can bypass the plugging the DVB-T into the PC and using that as the server.
http://www.trimedia.co.uk/product.asp?id=204

Originally Posted by popper

well , what do you know, you could get these in 2004, shame your local computer shop still doesnt have anything like them ?, they come on a DVB-T form to (no AVC/H.264 though)
http://www.trimedia.co.uk/product.asp?id=202
"
H.264 MP@L3 D1 resolution up to 2Mb/s
MPEG-2 MP@L3 D1 resolution up to 10Mb/s
Supported by Trimedia Middleware and Conditional Access
Flexible audio and video output via cable options
USB 2.0"
the The Net100 at the bottom of the page is rather nice
as it means you can bypass the plugging the DVB-T into the PC and using that as the server.
http://www.trimedia.co.uk/product.asp?id=204

H.264 Main Profile at level 3 is MPEG4 SD.

[popper]

arr yea, well its been 2 years, perhaps they make an updated one (with MBAFF support LOL)

Originally Posted by popper

arr yea, well its been 2 years, perhaps they make an updated one (with MBAFF support LOL)

I'm not aware of any realtime MPEG4 HD encoders which have implemented MBAFF, yet.

Anyway, the numbskull from Telewest is in charge of future developments, and he's decided HD will stay with MPEG2.

[HandyMac]

Gosh! Thank you for such swift responses! It's nice to have immediate access to people who have a clue what's going on!

I forgot to mention (I didn't want to over-complicate the arrangement!). Our ACTUAL installation consists of the following:

1) NTL wallbox supplying cable modem feed. Unsplit.
2) NTL wallbox supplying TV feed. Unsplit.
3) NTL wallbox supplying upstairs TV's. Split x2.

The upstairs wallbox (3) has been split to feed TV's in 2x bedrooms. One of those is actually a PC in my son's room with a TV card. Seeing great picture quality so I have no reason to believe that the signal is a problem.

I imagine that when (3) was added (about 3 months ago) the NTL engineer did whatever he needed to in order to bring up the signal on that additional pace box. Only at that time there was no 2nd TV connection, he "tuned" the connection for one PC on an extra pace box.

What I'm looking to do is feed MY PC with a TV feed from (2), or ideally (1).

Have looked at supplying a signal from an external aerial. The result was this (re-arrange letters).

A

[popper]

the chances are great that the 1 and 2 are infact a split, as its unlikely they feed 2 cables to your house from the cab.

when you say 'Have looked at supplying a signal from an external aerial.' i take it you refer to analoge tv and not digital DVB-T ?.

with DVB, you eather get it great, or massive blocky bits, or even not at all, the DVB way is far better than analogue in that when it gets a good signal, you are seeing the full quality potential in that .ts (stransport stream) and you would use something like MPC or VLC to just play back your .ts recordings (bda drivers save .ts as default) for instance.

---------- Post added at 20:32 ---------- Previous post was at 19:59 ----------

i was going to upload 2 samples to my ntl space to show how analogue (taken off cable feed) and digital .ts (taken off DVB-T look but it wont let me upload to the ntl webspace doh.

the upshot is the analogue comes out at 49meg mpeg2 encoded with winDVr3.0 ( the only app able to encode without dropping frames on a amdXP 2400+) and looks almost like this in realtime unless you use Dscaler), and a dvb-t .ts at 29meg straight copy off the stream, the .ts beats the analogue by miles and you get AC3 sound to boot...

[HandyMac]

Agree about split as the cable comes into the house. ISTR not long after we moved in an NTL engineer shaking his head with a tut-tut expression when he looked at the white cable coming into the lounge wallbox - we'd had a few problems with the signal, and he reckoned that whoever had wired the house had used cheapo quality cable to run to that wallbox.

OTOH the NTL feed to the wallbox in my study is literally the other side of the wall to the NTL access point outside.

I am indeed referring to an analog aerial.

Our transmitter is ally pally, 30 miles away. Even with a high-gain 18 prong aerial mounted in the loft the signal was extremely if-fy.

I regret that I'm not familiar with DVB-T, so that's something that google is going to do me a favour with right away.....

.....okay, am slightly more up to speed with DVB-T now. Looks to me to be what was coming out of my freeview box when I bought one of those. Problem was that it couldn't get enough signal to make it work reliably. Saw a few channels but blockiness everywhere was overwhelming.

A

[popper]

yes, thats it, the fact that you are getting the 'blockiness everywhere was overwhelming' can be cured but it means getting that high-gain 18 out of the loft and on to your chimney or a pole above the roof ridge
(higher is better, with all analogue/digital tv and wireless networking even).

its generally thought that using a high gain arial in the loft is just a wast anyways, but if you wanted to play around with it , you might first consider making a massive ground plain reflector (the bit behind the coax input box) do a search for Yagi DIY and take a look at some of the DIY wifi/wireless yagi info for why the ground plain works for reflecting the directional signal etc.

you probably already know its always better to have line-of-sight to maximise your signal, and in the loft your probably lossing a vast amount of that.

on top of that iv generally found that the new DVB-T USB sticks have far greater sensitivity than my older freeview STBs so again, that will help a lot.

by the way, -C = cable, -T = terestial, -S = satalite, theres also a newer -S2 , but so far iv not seen '2' for the others, theres also a newer DVB-H for handheld devices.

Originally Posted by popper

the chances are great that the 1 and 2 are infact a split, as its unlikely they feed 2 cables to your house from the cab.

when you say 'Have looked at supplying a signal from an external aerial.' i take it you refer to analoge tv and not digital DVB-T ?.

with DVB, you eather get it great, or massive blocky bits, or even not at all, the DVB way is far better than analogue in that when it gets a good signal, you are seeing the full quality potential in that .ts (stransport stream) and you would use something like MPC or VLC to just play back your .ts recordings (bda drivers save .ts as default) for instance.

---------- Post added at 20:32 ---------- Previous post was at 19:59 ----------

i was going to upload 2 samples to my ntl space to show how analogue (taken off cable feed) and digital .ts (taken off DVB-T look but it wont let me upload to the ntl webspace doh.

the upshot is the analogue comes out at 49meg mpeg2 encoded with winDVr3.0 ( the only app able to encode without dropping frames on a amdXP 2400+) and looks almost like this in realtime unless you use Dscaler), and a dvb-t .ts at 29meg straight copy off the stream, the .ts beats the analogue by miles and you get AC3 sound to boot...

I'm not sure exactly what you are doing to obtain your feeds, but the bitrates you mention are in no means accurate. Cable also does not include AC3 at the moment.
An entire cable transport stream (with 10 video sources) is approx 38 Mb/s at 64QAM. Satellite is 34Mb/s at DVB S (again typically 10 sources).
DVBS2 is used by Premiere and Sky for their HD ( the Beebs feed is DVB S, with 2 MPEG2 streams as well).

The broadcast quality encoders do not drop frames (guaranteed) hence why they are more expensive.