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Topic # 14282 25-Jun-2007 19:05
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I want to split my satellite feed so I can feed two tuners (in this case DVBS cards).

Do i just need a simple satellite splitter like the following:

http://www.dse.co.nz/cgi-bin/dse.storefront/467f68690137c1c8273fc0a87f330706/Product/View/L4036

This one shows 5-2400MHz as the range on it.  What is the range required for splitting freeview/sky?  Is a 5-1000MHz splitter sufficent?




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  Reply # 75913 25-Jun-2007 19:15
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The LBand IF used by Satellite systems runs from 950MHz to 2050MHz so it needs to be 2.4GHz rated. The actual IF sector used depends on the LO of your LNB, regardless they still will be somewhere in the above band.

Dont forget that if you want to split the signal to a Sky STB and a FTA STB/Card at this point (untill sometime next month) there is a mixed polarity issue that a simple splitter will cause you trouble, but if you want to feed two FTA tuners for FreeView, then a basic splitter is fine, just needs to be 2GHz or thereabouts rated.

Cyril





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Reply # 75915 25-Jun-2007 19:30
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Thanks Cyril

Just splitting freeview this time... bought a splitter on trademe - thought it was a 2.4 gig one but the picture the seller used was different to the actual splitter he delivered :(  I'll get the right splitter and try again...!




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  Reply # 75917 25-Jun-2007 19:45
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Regs, I got a 4-way splitter from freeviewshop.co.nz that I'm using to split my freeview signal between two dvb-s cards. They seem to have a good range an are pretty cheap too.

Rhys








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  Reply # 75926 25-Jun-2007 21:30
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rhysb: Regs, I got a 4-way splitter from freeviewshop.co.nz that I'm using to split my freeview signal between two dvb-s cards. They seem to have a good range an are pretty cheap too.

Rhys





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  Reply # 75927 25-Jun-2007 21:32
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rhysb: Regs, I got a 4-way splitter from freeviewshop.co.nz that I'm using to split my freeview signal between two dvb-s cards. They seem to have a good range an are pretty cheap too.

Rhys


thanks for the tip.  i saw a 2 way splitter in DSE today when for about $11 that specified the 5-2400 range so i'll probably just pick one of those up.




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  Reply # 75939 26-Jun-2007 07:49
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At 1.75GHz a 2way splitter has roughly 5dB loss (1/3 the power that goes in comes out), a 3way splitter has 10dB loss (thats 1/10 the power that goes in comes out), a 4Way splitter has 11dB loss. 10meters of RG6 has roughly 2.5dB loss.

So if you dont need more than 2ways then dont use a 4way as that a lot of signal to throw away. An LBand IF is delicate enough without being heavy handed with it.


A 4way splitter consists of three 2way splitters cascaded, a 3way splitter is interally identical except that the 4th port is not available nor terminated, hence only a 1db loss diff between a 3 and 4way.

Cyril

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  Reply # 75947 26-Jun-2007 10:44
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cyril7, thanks for the info, I didn't realise it lost that much signal going through the splitter. Does it work ok putting an inline amp before the splitter?

Rhys






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  Reply # 75949 26-Jun-2007 10:55
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Dont use an amp unless you need it. Ideally a system loss of 20dB is a much as you should aim for, however you can go up to 35odd dB before things start to turn turtle. Based on 20dB, thats 40meters of cable between the dish and the STB via a 4way splitter, or 60meters of coax and a 2way splitter.

Most STB's have a 40dB working dynamic range, the level leaving most typical LNBs is normally pretty close to the top end of that, so if you insert a 20dB gain amp and dont have 20dB (80meters of coax) worth of loss then you will most likely end up in a worse situation by overloading the STB. Also the amp will decrease the C/N ratio which is more critical than maintaining a high signal level into the STB.

If you have good/acceptable signal readings and low/usable BERs (or high quality) then its fine.

I guess my main original point is that there is a significant increase in loss by going from a 2way to a 4way, so if you dont need the ports why add unwanted losses.

Cyril

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  Reply # 75951 26-Jun-2007 11:05
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so does that mean that any 'loose ends' of cables (ie ready to plug into a STB, but not plugged in) are contributing to signal loss for Sky digital?

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  Reply # 75952 26-Jun-2007 11:16
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Even worse, they provide reflections that can cause distortion of the signal going to other STB's especially if there is quite a few meters of unterminated cable on a splitter output. Its true that the reflected signal in say a 4way splitter is at worst 20dB down, but it still will cause issues.

. If you go to Mastertrade or other electrical suppliers you will find 75ohm F terminators, othewise remove any unterminated cables from the splitter until needed. This also is not ideal but better as the unterminated port of the splitter is so close to the splitter that reflections are normally short enough to not be an issue, but ideally terminate them if you can or use a splitter with as few outputs as you need as previously discussed.

Cyril

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  Reply # 75969 26-Jun-2007 14:27
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thanks Cyril, will do that

next time the Sky tech comes around I might get him to have a look at the setup here. There are a hell of a lot of unexplained and unused/unterminated cables here.

is it one of these (http://www.dse.co.nz/cgi-bin/dse.storefront/46807a9c0062597c2740c0a87f3306ed/Product/View/P2280) I need?



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  Reply # 75974 26-Jun-2007 15:08
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allstarnz: thanks Cyril, will do that

next time the Sky tech comes around I might get him to have a look at the setup here. There are a hell of a lot of unexplained and unused/unterminated cables here.

is it one of these (http://www.dse.co.nz/cgi-bin/dse.storefront/46807a9c0062597c2740c0a87f3306ed/Product/View/P2280) I need?


I dont think a BNC terminator is going to be much use to you in this case - BNC uses a different mechanism than f connectors.  There is an f type terminator in this pack at dse, but i cant see one for sale seperately: http://www.dse.co.nz/cgi-bin/dse.storefront/46807a9c0062597c2740c0a87f3306ed/Product/View/L0172

there is a terminator by itself for sale here: http://www.freeviewshop.co.nz/f-type-75-ohm-terminator-plug-p-106.html




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  Reply # 75983 26-Jun-2007 16:54
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Regs has got the right part, dont use BNC ones.  Most electrical suppliers (MasterTrade, Corys etal) have the terminations, for similar if not less price.

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  Reply # 76036 26-Jun-2007 20:13
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cyril7: Dont use an amp unless you need it. Ideally a system loss of 20dB is a much as you should aim for, however you can go up to 35odd dB before things start to turn turtle. Based on 20dB, thats 40meters of cable between the dish and the STB via a 4way splitter, or 60meters of coax and a 2way splitter.

Most STB's have a 40dB working dynamic range, the level leaving most typical LNBs is normally pretty close to the top end of that, so if you insert a 20dB gain amp and dont have 20dB (80meters of coax) worth of loss then you will most likely end up in a worse situation by overloading the STB. Also the amp will decrease the C/N ratio which is more critical than maintaining a high signal level into the STB.

If you have good/acceptable signal readings and low/usable BERs (or high quality) then its fine.

I guess my main original point is that there is a significant increase in loss by going from a 2way to a 4way, so if you dont need the ports why add unwanted losses.

Cyril


Cyril, what is the C/N ratio?

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  Reply # 76068 26-Jun-2007 22:34
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C/N is Carrier to Noise ratio, this is the only thing that is important, it will dictate what BER the system will achieve, signal level can be right at the bottom of the scale, but if the C/N is adequate, then all is well.

Cyril

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