hook 2 stb's to 1 lnb

kamaleon

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#1
Hi all, me got a bit of a question:

can i hook one lnb only up on 2 different receivers
(i've got a ss2 pci on my desktop and a usb one on my laptop)
with something like this:
http://www.internet-par-satellite.com/asp-boutique/boutique/images_produits/images_maxi/18520.jpg
http://www.satnet.fr/pix/articles/coupleur.jpg
??

it'd be quite nice not to have to unscrew me cable everytime i want to use a box or another...

cheers for your support ;)
 

rolfw

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#2
Can't follow the second URL, but a twin LNB on the dish would be a better bet than the splitter, although if you are only using one of the receivers at a time, then it may work OK.
 

kamaleon

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#3
Yes, i'm actually waiting for a quad, but one lnb via a splitter has the advantage of having one cable only going across my flat :)

the splitter on the 2nd link is basically the same: 1 way in, 2 way out
i was wondering if, assuming it works:
- could i tune 2 different channels in on same transponder on my 2 boxes;
- what happens to 2x 14volts being sent by the 2 boxes? does the splitter have a resistance, does it send the voltage in serial...?
 
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#4
no, 2 or more sat receivers can't share a 1 output lnb, for why see my multiswitch guide below in faqs.
 

kamaleon

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#5
Hi spiney, could you precise which faq exactly is that?
 

kamaleon

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#7
gosh, will take me ages to read that :)
 

kamaleon

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#8
Say spiney, i've *vaguely* went through your faq, but i still can't understand... why can't i hook me two boxes to me lnb this way, if i'm only turning one of the boxes on at a time?
 
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#9
bid0n said:
gosh, will take me ages to read that :)
the main attribute with spiney is thoroughness, which i love.

he's taken along time to write that, so respectfully read it fully:D
remember they say a little knowledge is dangerous (i should know):-doh!
 
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#10
bid0n said:
Say spiney, i've *vaguely* went through your faq, but i still can't understand... why can't i hook me two boxes to me lnb this way, if i'm only turning one of the boxes on at a time?
Well, my guide does say, fairly clearly, but ......

Each dbs satellite transmits in a 2 Ghz bandwidth, on both vertical and horizontal polarisations, which makes a total bandwidth of 4 Ghz.

To get all that direct to a sat receiver, you'd have to actually use metal waveguide, completely impracticable in a consumer product (would cost several thousand pounds, maybe tens).

So system used is to "downconvert" the received 12 Ghz ku band to 1-2 Ghz so-called "satellite intermediate frequency", in the lnb, which allows much cheaper coaxial cable to be used.

Even reduced bandwidth 2 Ghz won't "fit" onto a coax. Therefore, the received 4 Ghz bandwidth is divided into 4 different so-called "polarities", each 1 Ghz wide, which "comfortably" travels down coax in TEM mode, though it's still high loss and special sat cable is needed.

The sat receiver then "choses" which polarity it wants, out of 4, by sending control signals back up cable to lnb.

If 2 sat receivers, or more, share a single lnb output, then there's only a 1 in 4 chance they'll want the same polarity - with just a quarter of total channels - otherwise their control signals will clash. Depending, it's possible to have neither of 2 receivers getting the wanted channel, and adding more receivers just makes things worse.
 

kamaleon

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#11
RIght. That doesn't explain why things would be messed up if i'm only turning on one stb at a time...???
 
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#12
In fact, bidOn, that DOES explain, but let's take a specific example .....

The control signals back up cable to lnb are 14/18 volts, and 22Khz (or no tone). When 2 receiver outputs are "mixed", whichever reciever sends 18 v forces horizontal polarity, and whichever sends 22Khz forces hi band. Now suppose:

receiver 1 wants a channel on hi band vert, so sends 22k / 14v.

receiver 2 wants a channel on lo band hori, so sends (no tone) / 18v.

Now, both receivers will get hi band hori, so neither gets the channel it wants!

Clearer?
 

kamaleon

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#13
Not at all. But maybe i'm just blatently STUPID...

If i am only turning ONE of the boxes ON, NOT THE TWO of them AT THE SAME TIME, then why would "receiver outputs be "mixed"" as you said??

the only purpose of me wanting such a solution is to prevent me from having to screw/unscrew my cable everytime i want to use a box/ or another BUT NOT AT THE SAME TIME....

can you please explain now? but if i'm just dumb, then by all means, i'm really sorry and i will not bother you anymore...
 
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#14
Well, ok bidOn, you've emphasised that point, but I thought the actual question was "why not 2 receivers at once?", so maybe I'M being stupid!

It depends how they behave, on being depowered. If the lnb input presents a high impedence, then fine, it's just like only having one receiver connected! But, that doesn't always work, even when it says "loopthrough".

(added) looking at your original post, it does look like using 2 receivers at once!

(added) if using a coupler, be careful about which connections have "power pass".
 

kamaleon

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#15
Yes, you're right, originally, it was "at once", but as that seemed to not be possible, then i thought "oh well, then not at once", and halfway trough the post i thought i'd left that clear... whilst the answers i kept getting didn't seem to reply to that...

Your answer now explains me quite a lot! Seems we're getting on the same wavelenght now :)

Ok, so final question: let's assume it works ok with one of the receivers off. Let's imagine i turn on the one that was off, with it previously set on the same transponder than the one that was already on... what happens? :D
 
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#16
I didn't quite follow that, but ......

(Obviously), you can have 2, 1, or no receivers switched on!

Assuming a "power pass all ports" splitter .....

Assuming both receivers "behave" - when switched off - so that neither presents a short circuit at sat if frequencies, then if just one on is no problem.

If both on, then it's as I just described, there's a 1 in 4 change of both receivers wanting the same polarity, if that's so you're lucky, but otherwise one or both won't get the wanted channel.

(Unless you want the same channel on both, that's never a problem!).

Otherwise, with power blocking one or more ports, 22Khz still always overrides no tone, but only the power pass port controls 14/18v, so you have to work out what will happen for specific splitters ......
 

kamaleon

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#17
ok, so ideally what's the thing i need in order to use both receivers, a 22Khz switch?
 
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#18
The easiest thing is just get a sat splitter with FULL power pass, on all ports. Then, you can have either receiver powered, by itself, with full lnb control, and with both powered together it's as I said.

There's no way round this, you can't get all channels with 2 or more receivers off 1 lnb output, whatever gadgets you use. Only a muti output lnb (or a quatro feeding a multiswitch) "does the trick".
 

kamaleon

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#19
erm... just did a google image research for "sat splitter power pass" and the stuff that came up didn't seem any different than the links i posted earlier... so it leaves me wondering... have you got a handy link with one to illustrate what you've just stated?
 
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#20
i use a splitter a all ports power pass on my manhattan and ss2 card seems to work fine had no problems yet.
 
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