Split a wideband lnb signal

Pride Of Cucamonga

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Hi, is it possible to split both of a wideband LNB's outputs (H and V) between two receivers without a significant degradation of signal? Would there be any power issues? Assume I would turn the LNB power off on one of the devices. cheers
 
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2cvbloke

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Generally not a good idea, even if you turn LNB power off on one receiver, the other will control the LNB's output, so if Receiver-A is in say Vertical-High, Receiver-B will only be able to receive channels in that range. Best option is to use another output from the LNB, assuming one is free and the dish is easy enough to access... :)
 

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Generally not a good idea, even if you turn LNB power off on one receiver, the other will control the LNB's output, so if Receiver-A is in say Vertical-High, Receiver-B will only be able to receive channels in that range. Best option is to use another output from the LNB, assuming one is free and the dish is easy enough to access... :)

I was assuming this is for a SkyQ (or similar ) system, where each of the feeds is polarity switching independent.

If so, the overall signal level would have to be 3dB above threshold, in order for the splitting to work successfully
 

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I only see mention of a SkyHD box in their profile, but I could be wrong though... :)
 

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If it's a sky type wideband LNB, one output is V and the other is H, so 2 simple voltage pass UHF/IF splitters should be fine, you will lose 5 or 6db, but even with a standard minidish the output at the LNB will be 74-80db, as long as it isn't an excessive cable run, then it should work.

You can always use a couple of wideband line amps, as used with stacker destackers to boost the signals before the splitters.
 

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Cheers all. Yes, it's for a Sky Q LNB split to a Sky Q box and a SATP>IP server.

If it's a sky type wideband LNB, one output is V and the other is H, so 2 simple voltage pass UHF/IF splitters should be fine, you will lose 5 or 6db, but even with a standard minidish the output at the LNB will be 74-80db, as long as it isn't an excessive cable run, then it should work.

You can always use a couple of wideband line amps, as used with stacker destackers to boost the signals before the splitters.

I never quite understand decibels and signal strength. How many metres of average quality cable would you lose the same 5 or 6 db over?
 

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Signal strength is usually measured on your satellite receiver by the RSSI voltage (Received Signal Strength Indicator) coming out of the satellite signal de-modulator, this voltage can be any DC voltage depending of the incoming signal strengths, the voltage is then translated by the recivers software to provide an indication on the screen as the "S" signal.

dB is used for a determination of loss or gain in a system, in the RF world dB is usually indicated as dBm, (dB plus or minus at 1 millivolt)(or lower voltages like uV or pV) a standard RF signal 2 way signal splitter used for TV or satellite is around a -3 dBm per port, this is equal to 1/2 the incoming RF signal at each port.

Normal RG-6 coax used for satellite work has a loss of about a -6.2 dBm at 1 GHz per 100 feet, this loss can be higher or lower depending on the frequency used, at 1 MHz it would be about .2 dB, at 10 MHz it would be about .6 dB, at 100 MHz it would be about 2 dB, so you see the higher the frequency the higher the loss. Also the coax has a bandwidth frequency rating, the normal coax used for TV or cable has about a 5 to 900 MHz operating bandwidth, the coax used for a satellite system needs to have a higher top end, usually around 2.5 to 3 GHz.
 

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Most of the UK installation trade use dbµv (microvolt), so will be positive figures, 10m of good quality RG6 satellite cable loses anything between 20 and 30dbµv per 100 metres for the 1,000 to 2,150mhz range. For a standard universal LNB, it is recommended that there is a minimum of 60dbµv ish at the receiver (I prefer a little more), Sky seem to think that for Q it should be a little higher, hence why they tend not to use WF65 cable (smaller core) as much for Q installations which has a higher through loss 0f 30-50dbµv per 100m.
 

Pride Of Cucamonga

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Really useful guys, much appreciated. Although most of the additional IF bandwidth going down the Sky q cables is at the lower frequencies, it does also add a couple hundred MHz extra to the top too - up to 2350MHz - so I think that’s why Sky Q requires better quality cable.

Would a splitter like this work? Could sending Lnb power from one receiver cause damage to the other receiver?

 

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I wouldn't use a splitter with power pass on all ports. I would use one with power pass on one port only and put that to the Q box.
 

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That is a splitter with one-way power pass on both ports, that is good.

For cases like this, you need diodes in your splitter, to prevent power from one receiver to reach the other receiver. The arrows on the splitter indicate the one-way power.
Either receiver (or both) can thus supply power to the LNB,

Greetz,
A33

written on my eeePC with Puppy Linux.
 

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Sorry A33, I must disagree.

There is no indication that there are diodes inside the splitter and therefore the only safe option is a splitter with DC power pass on one port only. I do not take the arrow as indication of direction of current flow, only that there is no block to DC of either polarity.
 

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Well, if you must....

There are plenty splitters around with all ports power pass, one way (with diodes). For one thing, they are needed for using Unicable/JESS on multiple receivers.
The usual way for indicating the power pass one way is such an arrow, as on the picture. For two-way power pass, normally a double pointing arrow is used, or no arrow, AFAIK.
Edit: In fact, finding a splitter with two-way power pass is not always easy. Many power pass splitters are one-way power pass, I noticed, when using diseqc devices in a parallel setup. I really had to look for one...

Of course the added picture at a website is not always matching the offered article. And sometimes the picture on the item itself is wrong.
So checking for the presence of a diode (with a multimeter) is never wrong.

But from the picture I'd say, that is just the splitter DeadHorse800 needs.

greetz,
A33

Edited: Line added.
 
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If he wants to power the LNB by just one box, these would be OK, indeed.

If he wants to have the ability to power off one box, and then power the LNB by the other box, then with such a splitter that is not possible.

Greetz,
A33
 

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If the Q box is anything like a Digibox or its PVR derivatives then the LNB will be powered regardless of whether the box has been put in standby or not. So the LNB will provide H and V output providing the Q box is plugged into the mains.
 

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If he wants to power the LNB by just one box, these would be OK, indeed.

If he wants to have the ability to power off one box, and then power the LNB by the other box, then with such a splitter that is not possible.

Greetz,
A33

yes, the first one


thanks, they have to go to 2350MHz, although for astra 28.2 it's just a bunch of feeds up in the high frequencies so doesn't really matter if only 2300MHz, but be nice to do it properly

seen these - would they be ok?
VISION 2-Way Splitter DC Pass 5-2400MHz LED Indicator: Amazon.co.uk: Electronics
Labgear WBOS2F 2Way Outdoor Splitter in Weatherproof Casing: Amazon.co.uk: TV
 

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Yes, Vision one looks good. Reference the directional voltage indication, I have tested some to see if the direction is truly one way and found that the ones I tested were, although it was quite a while ago, so can't remember which ones they were.
 

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Why not use a satellite switch? a legacy (voltage switching) 4x4 switch (+13v/+18v in to 4 single out) would give independent transponder reception at both receivers.
 

Pride Of Cucamonga

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Why not use a satellite switch? a legacy (voltage switching) 4x4 switch (+13v/+18v in to 4 single out) would give independent transponder reception at both receivers.
Thanks, I’m really just looking for the cheapest and simplest solution possible. Is there an advantage to this?
 
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