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Parellelling of Coaxial Cable TV – Signal Quality

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May 18th, 2011 at 3:46pm  
Let us consider the foll scenario where we don’t have Sat TV, but only Cable TV.

I wish to connect the Main Cable TV Input from the Cable Operator, as follows :
a) To Cable HD-STB to Main TV 1
b) Also parallelly (parallel connection taken BEFORE the connection to the above TV 1 STB) connect DIRECTLY to Secondary TV 2
See attached Sketch : Coax_STB&Direct_Setup_Fig-2.jpg

Will this type of Paralleling at the Cable TV Input Cable work satisfactorily ?

By the above paralleling, how much will the deterioration of the signal be (eg, loss in dB value) for :

i) Main TV 1 (ie, how much will the loss be when compared to a single connection only to this Main TV 1 thru it’s Cable HD-STB ie, if we don’t have a parallel connection to Secondary TV 2) ?

ii) loss of signal for the Secondary TV 2 (ie, when compared to a situation, where we have just this single Secondary TV 2, and connected directly (without any STB) ie, assume just for this comparison, that we don’t have TV 1 and Cable HD-STB to TV 1 at all.)

I would like to know the deterioration level for Std TV Signal and for Full HD TV Signal, in EACH TV, due to the above paralleling.

Thanks in advance (TIA)

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Reply #1 - May 18th, 2011 at 5:11pm  
Where the incoming cable splits into two,  you need a device called a "2 way cable TV splitter". It has one input socket and 2 output sockets, similar to this:
....
It is intended to divide the signal power equally, over a range of perhaps 5 - 2000 MHz, and reduces both the signal level and the noise level by half (nominally -3 dB at each output).

Provided that the signal level and signal to noise ratio is not already marginal I doubt that you will notice much difference.  If you do have signal quality problems then what you need is a cable TV amplifier, followed by the splitter.  In this case consult the service provider. They may be able to simply increase the power to your particular outlet by 3 dB and if not, provide you with advice about suitable booster amplifiers, ideally incorporating 2 or more splitter outlets.  

I'm not sure quite what you mean by "cable TV".

Some modern all digital systems require that a set top box be located between the cable system and your TV. If this is the case you need one set top box prior to each TV set.  

If your system is such at a directly connected TV will receive some programmes then the lack of a set top box for is OK for the ground floor TV set.

My guess it that you have a cable system with a mixture of carriers, some older carriers suitable for direct TV connection and some new digital HD carriers requiring a set top box.

If you leave out the "2 way splitter" then signal levels at the two ends are very uncertain and will vary from one frequency to another such that some channels will work and others will not.  This is due to the mismatch caused by connecting two 75 ohm cables to a single incoming 75 ohm cable.  The signals bounce up and down the cables and add and subtract according to the exact  length of the cables and the frequency. Not good !  If you have HD digital carriers then your service provider probably insists that you properly terminate your cable ends to avoid interference to other people.
Every cable or outlet should be terminated in a 75 ohm device.

Best regards, Eric.
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Reply #2 - May 18th, 2011 at 6:20pm  
To select the correct splitter, more info is required. Is your cable signal analog or digital. And does the signal support basic receive-only televisions, or is there a return signal involved? I.E. interactive TVs, video on demand, internet content TVs, etc.

//greg//
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Reply #3 - May 19th, 2011 at 11:10am  
Forum Admin / Eric,
Thanks for properly placing the 4 images, where they were apt, in my Posts.

In this Post, I have given sendspace ref for another Fig 5.

*********

You have asked what I mean by “Cable TV”.
Ans : Well, I am referring to the Coaxial Cable TV, which the local Cable Service Provider (CSP) / Cable Operator (CO) provides to large number of Residences in our locality – as opposed to Satellite D2H TV Input.
You have also used “Cable TV” when referring to : "2 way Cable TV Splitter".

*********

The Existing “Cable TV” Setup in our locality / my house is as follows :
(Pl refer to my Sketch : “Coax_STB-PC-Drct_Thr-Spltr_Setup_Fig-5.jpg”, downloadable from : http://www.sendspace.com/file/t6vuvp)

This Fig 5, is a modified version of Fig 2 posted earlier ; this Fig 5 gives a more realistic Current Existing Status.)

I have spoken to the Cable Service Provider (CSP) Rep, but he is not an expert. I am giving below my guess / understanding of what “may” be currently available here :

a) The CSP is currently providing only Std TV signals, not yet the HD signals to our Area, but HD signals will soon come, probably within 6 months to 1 yr.

b) As of today, I have a Direct Cable Connection from the CSP, connected to my Old TV (TV 2 in the Sketches) in the Gnd Flr ; I have connected a “local brand” Splitter (ie, local => no Mfr Name ; they may not even know what impedance they have “matched” !) at the Old TV 2 location, and taken a T-Off to my D/Top PC, which has a Pinnacle PC TV Card.
In spite of the local splitter, the reception in TV 2 has not suffered drastically.

In Fig 5, the connections marked in Orange Colored Tick-mark indicate that the Cable first reaches the wall socket location near the Old TV 2, from where, via the Splitter “CS-2”, one Output is taken to TV 2, and another to the PC in the Top Flr.

c) The CSP has also got 2 types of STBs to offer :
i) Ordinary STB (his own “local” make, probably compatible with his whole Setup) – which, many in our locality are already using ; the CSP claims that the clarity will be better with it.
ii) HD-STB (again, his own “local” make, probably compatible with his whole Setup) – which is 4 times expensive, and no one in our locality is using (perhaps, a few are using in another area, also serviced by him)

I have shown both these options for the Main TV 1 in Fig 5 above.

We have already identified the Brand / Model of the “Main TV 1” to be purchased – it is “Sony Bravia, Full HD-3d Ready, LED Edge-Back-Lit, KDL-40 EX 720” ; we may buy it in the next 10 days.
That is why, I first drew the Overall Proposed Setup – Fig 1 Sketch.

Initially, I do not want to buy any branded Sat D2H Operator’s subscription now. I would like to use the existing CSP’s Cable, buy the necessary Splitters, STB (Ordinary or HD version) etc.

Also, parallelly, I want to try the FTA Channels route as a Hobby (meaning that even if my experiments fail, it still does not stop the family from viewing the TV Channels through Cable).
I want the FTA Channels experiment to be a “better than average” setup – with Motorised Dish, USALS compatible Cabling, Quad LNBs, each LNB fully remotely controllable etc, so that I can experiment by focussing on diff Satellites from time to time.
That is why I wrote the list of Specs that would make for a very good DTA or STB Receiver, capable of receiving HD signals in good quality from diff Satellites etc.

*********

Now, may queries on just the “Cable TV” part, for now, based on the above, are as foll :

Q1 : Are there 3-Way Splitters available in the Market ?
- Pl let me know the Top 2 Brands & Models of 3-Way Splitters in the market (ie, in US, in Europe, in India).

- Pl also let me know the Top 2 Brands & Models of 2-Way Splitters in the market (ie, in US, in Europe, in India).


Q2 : What is the loss in dB in EACH of the 3 Outputs from a 3-Way Splitter ?
You mentioned that it is about 3 dB Loss for a 2-Way Splitter.


Q3 : If I buy these Splitters, and Quad LNBs in the US, will they work well in India too ? ie, I hope the standards are universal / compatible in all the countries for such grass-root-level essential items ??

The reason is, that in the US, these products are more easily available as “off-the-shelf” with some details of the specs that we are actually paying for.

*********

Now to respond to Reply 2 from USN_Retired :

a) The Cable signal from the CSP may soon have HD Channels too (within 6 months), when he may advise us to buy his Cabel-HD STB.

b) This New Sony TV 1 allows Web Browsing of selected 18 websites like YouTube, some Sony Channels etc.
But this Internet Browsing “pathway” has nothing to do with Sat Dish Internet ; this Internet Browsing pathway is provided by 2 ways :
i) a Direct Physical Wire from the BB Router (the Home Routers usually have 4 Physical Ports).
OR
ii) Wirelessly connect to Internet via the Router using an expensive Dongle that uses up one of the 2 USB Ports provided in the TV.

I have a Router, and I would be connecting a 30 Ft (9 m) long Direct Physical LAN Cable to the TV’s LAN Port from one of the Router’s 4 Phy ports (one Phy Port of the Router is already connected to my Main D/T PC, the PC, shown in Fig 5.

So, in this way, while this New TV affords me Internet Browsing, one cannot still probably call this “Interactive TV” ??

***********

Since I have explained a bit about FTA Channels Experiments as a Hobby in this Post, I request you to also refer to :
http://www.satsig.net/cgi-bin/yabb/YaBB.pl?board=point;action=display;num=130417...
- Post # 4 dt 14th May, 2011
- and Post # 12 dt 19th May, 2011
where, I have raised the query regarding Elevation Angle adjustment Remotely from the STB.

***********

TIA

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Reply #4 - May 20th, 2011 at 11:29am  
Splitters normally have 2, 4, 8 or 16 outlets. Passive splitters have output levels nominally -3, -6, -9 or -12 dB down.  Expect a further 1 or 1.5 dB loss.

...
See:
http://cpc.farnell.com/jsp/level5/module.jsp?moduleId=cpc/264225.xml
Active splitters incorporate amplifiers to keep signal levels up.

Terminate unused ports for best results.

Best regards, Eric.
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Reply #5 - May 24th, 2011 at 8:41am  
thank you so much by providing the nice information  i was also facing this problem but now i have solve it due to your lead providing in this forum and thanks for it
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