Understanding Legacy, Dishpro, and Dishpro plus LNBs and switching

[grasshopper]

C/P

The term legacy refers to the first methods used to send satellite signals from the dish to the receiver. In the beginning DBS Satellites such as those used by both Dish Network and DirecTV only transmitted either odd or even transponders. Each transponders carries as many as 20 individual channels. A transponder is best thought of as a cluster of channels.

When a transponder is broadcasted from the satellite each transponder needs a specific amount of clear frequency space on both sides of the main transponder frequency. This is called bandwidth. Any other signals transmitted with in that bandwidth space will interfere with the main signal. With DBS Satellite the frequency 12.224 GHz is Transponder 1. Transponder 3 is 12.253, TP 5 is 12.228, and so forth all the way to TP 31. Each transponder is separated by 29 Mhz(rounded off). Each Satellite Transponder needs .29 GHz or 29 MHz of bandwidth.

Transponder 2 on DBS Satellites is 12.239 GHz, only about 15 MHz away from both transponders 1 and 3. To avoid interference between the Odd and Even transponders. Satellites broadcast the odd and even transponders in different polarities. They use either Left Hand Circular Polarization (LHCP) or Right Hand Circular Polarization (RHCP). Think of a cork screw twisting towards the left or the right. If a LNB is set to receive Left Hand Polarity, then it will not receiver the Right Hand Polarity signals. This isolation of signals allows for the simultaneous use of both odd and even transponders without interference between them. DBS Satellites use Left Hand Polarization for Even transponders and Right-Hand Polarization for odd transponders.

To control the LNB for reception of either LHCP or RHCP, the receivers changed the voltage sent down the coax to the LNB. This is called voltage switching polarity. All Dish Network receivers use Voltage Switching Polarity when in legacy mode. Older "legacy" only receivers only work in this manner.

The limitations of this method become obvious when you wish to distribute satellite signals from a dish/LNB to several receivers. You must run a cable from each receiver to the LNB. Early LNB's only had two ports. To expand the number of receivers, special switches are required. These switches have two cables connected to the LNB ports and up to 16 spots for receivers. These switches are most often called by their input/output abilities. 2 in, 4 out became a 2 by 4 switch. A 2 in, 8 out became 2 by 8 switch

To accommodate the need for TV antenna signals, a third port is sometimes added. Using diplexors, an installer could use a single coax to carry both the satellite signal and local off-air channels from a roof top TV antenna. This third port changes the names of the switches to 3 by 4 switch.

When Dish Network started using a satellite dish which received signals from two locations, such as the Dish 500, another type of switch was created. The 2 in 1 out (SW21), and the 4 in 2 out (SW42) switch allowed a DISH receiver to control a switch that selected either one of two satellites. Think of these multi-sat switches as electronically controlled A/B switches. Soon after, DISH released the legacy Twin 500 and the legacy Quad. This LNB's incorporated two LNB and internal switches, eleminated the need for external switches.

The problem with using a Dish 500 with more than four receivers was the number of devices needed. Going beyond four receivers per dish came an exercise in the use of splitters, jumpers and more switches. Possible but not very pretty, and subject to increased signal loss. This meant short cable runs between all devices. A new method was needed to transfer the signals between satellite and receiver when using the Dish 500.

The Dish Pro (DP) LNB was created. Based on band stacking technology but enhanced with internal multi-sat capabilities, the DP LNB takes the odd and even transponders and brings them both to the receiver at the same time. Instead of the receiver switching voltage to indicate which polarity was needed, the receiver had access to all transponders. This had two advantages and one disadvantage. The first advantage was the ability to split the signal to more then one receiver. If you had a need for 6 receivers to receive signals from one satellite, you could split the signal without the need of switches. The second advantage was the removal of the voltage switching polarity control. The receivers supply a steady 19 volts when in DP mode. This allows for longer cable runs without the worry of voltage drop off. The disadvantage was the use of a full 1000 MHz or 1 GHz of bandwidth. Coax cable which worked Ok for Legacy installations may not meet the needs of a DP installation.

For multi-sat installations two coaxes are still required for signal distribution. One for 119 and the other for 110. The DP34 (3rd port for off-air) installed with two coaxes from the DP LNB and up to four receivers connected to the switch. The real neat thing are the two through ports. These ports can be used to supply signal to additional DP34 switches. Up to four cascaded switches are possible. Using a Single Dish 500, a series of DP34 switches and only two coaxes for trunk distribution, an installer could provide signal to 16 receivers for full access to both 119 and 110.

The next issue facing Dish was their introduction of the dual tuner receiver. These receivers have two tuners which can provided individual service to two TVs. The DVR receivers, can also operate in a mode which provides two tuners to one TV. This allows the user to record two shows or record one show, while watching another. The only problem is you need two coaxes installed to the receiver. Many homes are pre-wired with only one coax to each location. This meant installing additional coax cables in homes where the home owner was not expecting the need for more cables. After all, they were told the house was a wired and ready. Most the time the house not wired properly, but that is another story. To help solve this problem, DISH developed the Dish Pro Plus (DPP) LNB.

The DPP LNB has three connections. Two for receivers and another for mixing in signals from another dish. More later. The DPP receiver connections are unique in that they work on ALL dish receivers. Legacy and new models. The DPP LNB works just like a legacy LNB. It uses the 950Mhz - 1450Mhz (500 MHz bandwidth). It uses voltage switching polarity selection, but has another 500Mhz band at a higher frequency. This upper band is only accessible by a dual tuner receiver. The dual tuner receivers use the lower band for Tuner 2 and the upper band for Tuner 1. Each band can supply either odd or even transponders from either the 110 or 119 satellite. The third port connects to another dish installed with DP single satellite LNB. This dish is used for reception of additional DISH programming from satellites at 61.5, 129, or 148.

[shery20]

wel said gh

[Bud_Alcor]

Again GH thanks

[RagingBull]

I think you fingers must have calluses after all that GH. Great info.

[zekester]

I hope that was a C/P. great post.

[eclipsemoon]

great post my friend, i learn something everyday.

[gentry]

I can tell you love this stuff, and we certainly appreciate your sharing. THE more you Know....

Thanks again.

[kingsat13]

GH, let me say welldone!!!!
Its like I am in a classroom, whao!. Great job man...

[eddieg1234]

Just wondering if you had a DPP and one receiver like a viewsat you would not need a diseqc right. Then each port could push out 110 and 119 right. So you could actually have 2 box right.

[lamb88l]

Originally Posted by eddieg1234

Just wondering if you had a DPP and one receiver like a viewsat you would not need a diseqc right. Then each port could push out 110 and 119 right. So you could actually have 2 box right.

Right bossman.

[twincroft]

Thanks for that great post...very informative.....