# Simple LNB Explanation, Please?



## beejaycee (Nov 1, 2003)

Here's where I show my lack of understanding of the wonderful technology that allows me to enjoy the Simpsons! What is the inherent limitation of satellite reception that requires switches on the end of LNBs? Why can't the switching component be built integral to the receiver so that only one cable need be run from the dish into the house? It is a cost factor or a technology factor?

Allow me to expound upon my ignorance: are lnbs capable or receiving only one transponder from one satellite at a time? Or rather that they are limited to odd or even banks of transponders at a time? How do my 2 Tivos access 4 different transponders on one satellite at a time?

Thanks!


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## cdru (Dec 4, 2003)

beejaycee said:


> Here's where I show my lack of understanding of the wonderful technology that allows me to enjoy the Simpsons! What is the inherent limitation of satellite reception that requires switches on the end of LNBs? Why can't the switching component be built integral to the receiver so that only one cable need be run from the dish into the house? It is a cost factor or a technology factor?
> 
> Allow me to expound upon my ignorance: are lnbs capable or receiving only one transponder from one satellite at a time? Or rather that they are limited to odd or even banks of transponders at a time? How do my 2 Tivos access 4 different transponders on one satellite at a time?
> 
> Thanks!


As I understand it, older style LNBs would only receive the horizontal or vertical polarity of the signal. The external switch was required to choose between the two different signals. You'll see references to using an old primestar dish as a poor-man's superdish but many primestar dishes had seperate LNBs for each polarity..requiring 2 different LNBs.

Then came along dual LNBs that really had 2 lnbs built into one physical housing. They still required a switch, but everything was together. Then came twins which had the built in switch for 2 outputs and the quad which had 4.

Your Tivo has probably 2 different cables. Each cable can see the signal from one satellite, either even or odd transponders. Your switch has 2 or 4 cables coming from it to the satellite which carries each polarity from 1 or 2 satellites. By instructing the switch which polarity to switch to as well as satellite, it can see anything at the same time.

With Dish Networks DishPro, the cable coming from the satellite stacks the signal going to the switch. Both polarities go across the same cable and get unstacked at the switch. This means that fewer cable runs are required to get to the switch. Soon Dish will release a new switch that stacks two independent signals between the switch and the receiver. This would mean that a dual tuner system would only require 1 cable from the switch to a special diplexer that would unstack the signal.

Hope this explains it...and it's very likely I messed something up with my terminology along the way.


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## James Long (Apr 17, 2003)

Basic LNBs give you either odd or even transponders, block down converted to fit between 950 and 1450 MHz on the coax. The switch in the LNB decides what set you get, up to 16 transponders at a time.

The next level of difficulty is a stacked LNB. Odd transponders starting at 950MHz and even transponders upconverted above 1450. This feed could give you all 32 transponders on a satellite.

After that you have switches that allow multiple LNBs to be switched onto one cable. You get one satellite at a time, and depending on what kind of LNBs you have, up to 16 or 32 transponders.

E* has "Dual LNBs" with a switch built in that can switch between the LNB and polarity, and multiple outputs that can feed separate signals to separate receivers. I don't believe D* has "Dual LNB", but I add them for completeness.

A normal receiver can pick up ONE transponder at a time. Dual tuner receivers can pick up more than one, but still limited to what comes down the cable (one satellite or one polarity, depending on LNBs).

BTW: DBS transponders are Left and Right CIRCULAR polarity, not the Horizontal of Vertical seen on FSS and other bands. This is nice because the LNB does not have to be adjusted for skew.

JL


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## cdru (Dec 4, 2003)

justalurker said:


> A normal receiver can pick up ONE transponder at a time. Dual tuner receivers can pick up more than one, but still limited to what comes down the cable (one satellite or one polarity, depending on LNBs).


Do you know with the yet to be released DP44 switches, will it stack two different satellites on the same cable or must both tuner's signals come from the same bird?


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## James Long (Apr 17, 2003)

cdru said:


> Do you know with the yet to be released DP44 switches, will it stack two different satellites on the same cable or must both tuner's signals come from the same bird?


I'm not sure what black magic the DP+44 and DP+ LNBs are capable of. The interesting thing to note is that a DP+ feed can carry any of the four satellites input to feed two tuners. Which means it is more than a simple stacking.

I suspect they are stacking the satellite and polarity selected by one tuner at 950-1450 and the other satellite and polarity for the second tuner at 1550-2050 or so. There isn't room to stack all four satellites input to the DP+44 or three satellites fed from a DP+TwinLNB on a single cable 100% of the time. It must be switched!

Which limits DP+ to two tuners. I suppose a third tuner could use 450-950 on the cable IF they made a no-diplexer rule (or four tuners if they reorgainze to 50-550, 600-1100, 1150-1650, 1700-2200 - if the cable can handle it). Who needs three or more tuners in one box? (OK, nerds can put your hands down.)

JL


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## beejaycee (Nov 1, 2003)

cdru said:


> Then came along dual LNBs that really had 2 lnbs built into one physical housing. They still required a switch, but everything was together. Then came twins which had the built in switch for 2 outputs and the quad which had 4.


Here's where I go into dead-horse-beating mode! For clarity, let's say I take a Dish 500. I hook up two receiver cables to an SW21. Then I hook one cable from the SW21 to the LNB that points to the 119 slot. Can one receiver look at the odd transponders while the other looks at the even one? I think they can so does this mean that there are actually 2 LNBs inside each of the dual LNBs? So my Dish 500 w/dual LNBs actually has 4 physical LNBs?

I'll get this down yet!


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## JohnL (Apr 1, 2002)

beejaycee said:


> Here's where I go into dead-horse-beating mode! For clarity, let's say I take a Dish 500. I hook up two receiver cables to an SW21. Then I hook one cable from the SW21 to the LNB that points to the 119 slot. Can one receiver look at the odd transponders while the other looks at the even one? I think they can so does this mean that there are actually 2 LNBs inside each of the dual LNBs? So my Dish 500 w/dual LNBs actually has 4 physical LNBs?
> 
> I'll get this down yet!


Bee,

A DBS tuner either a single tuner receiver or one feed on a Dual Tuner receiver (IE DirecTIVO or Dish 721) needs direct control of its feed. Through a series of Electronic signals the receiver needs to send these signals to either switch the LNBF to a Different polarity or to signal a switch to another LNBF for a different orbital slot or both. Since a single tuner needs to select which polarity and or which Orbital slot you CAN NOT connect more than one receiver to a single Feed from a LNBF or a MultiDish switch.

A LNBF is a physical unit actually its the ANTENNA, The Dish is really just a the reflective surface used to gather enough radiated energy to resolve the signal in the LNBF (Low Noise Blockedown Feedhorn). Most LNBF's (duals) today have TWO seperate antennas that can be controlled independently of each other, so one DUAL LNBF can transmit one Orbital slot but only upto 16 transponders at a time to the receiver on each of the two feeds. A DISH TWIN LNBF can transmit one of TWO Orbital slots upto 16 transponders at a time on each of two feeds. A Dual Dish Pro LNBF can transmit one orbital slot but all 32 transponders at a time on each of the 2 seperate feeds. A Dish Pro TWIN can transmit one of two Orbital slots at a time but all 32 transponders on the each of the 2 feeds.

This is where the switches come into play, a SW21 switch can be used with a Dish 500 with two Dual LNBF's so that one feed from the 119 LNBF is combined with one feed from the 110 LNBF, now the receiver connected to the SW21 can send a signal to the SW21 to switch to either 119 or 110, once switched the receiver sends that selected LNBF to Supply either EVEN transponders or ODD.

A SW44 or SW64 switch is used with the same Dish 500 with two dual LNBF's. 2 feeds from the 119 LNBF one locked EVEN and one Locked ODD, then2 feed sfrom the 110 LNBF one locked even and one locked odd. Since the Switch now has all four feeds EVEN and ODD from both 119 and 110, the Switch's 4 seperate outputs can have access to all for possiblities without the need for the LNBF's to change state.

Dish Pro switches work somewhat the same but since the Dish PRO LNBF's can supply both Polarities at the same time only one FEED is needed for each Orbital slot 119 and 110 so the Switch only needs 2 cables from the Dish PRO LNBF's on the Dish to then multiplex in the Dish PRO Switch. The Dish Pro switch does basically the same as the SW44 or SW64 switch in that is provides all the neccessary switching and multiplexing to support more than one receiver with either or Orbital slot and polarity.

So as you see a LNBF is a LNBF no switch or combinations of switches will yield anymore LNBF's but can you support more than one receiver from one LNBF if combined with the right combinations of switches. Again the receiver needs to know which types of LNBF's and Switches its connected too, so it can send the correct series of electrical pulses and signals to trigger the Switches and LNBF's to provide the correct signal for the channel the receiver needs to tune, again since this is the case the receiver is always in a ONE to ONE arrangment one Receiver or TUNER to ONE Seperate FEED.

John


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## James Long (Apr 17, 2003)

beejaycee said:


> Here's where I go into dead-horse-beating mode! For clarity, let's say I take a Dish 500. I hook up two receiver cables to an SW21. Then I hook one cable from the SW21 to the LNB that points to the 119 slot. Can one receiver look at the odd transponders while the other looks at the even one? I think they can so does this mean that there are actually 2 LNBs inside each of the dual LNBs? So my Dish 500 w/dual LNBs actually has 4 physical LNBs?


The first note to make is to look at the names of the switches.
SW21 takes two LNBs and feeds 1 receiver,
SW44 takes four LNBs and feeds 4 receivers, and
SW64 takes six LNBs and feeds 4 receivers.
DP switches do that trick with stacked "DishPro" LNBs:
DP34 takes three DP LNBs and feeds 4 DP receivers.
(DP34's can also be expanded, so a second or third attached DP34 feeds an additional four receivers each.)

Note that the first digit is the number of LNBs and the second the number of receivers. You cannot take a SW21 and reverse it to connect two receivers to one feed. That would be an SW12 ... and those are not made. 

Look on the outputs of your legacy single LNBs. If you only have one connector it is only capable of putting out one polarity at a time. If it has two connectors it can put out EITHER odd OR even on each cable ... voltage switched ... from the same LNB. If you have two feedhorns on the same LNB (white disks facing the dish) then you have a dual LNB.

JL


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