MultiLNB Switch Setup

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If you want to receive channels from more than one satellite then you have a number of options. Two of the more common ones are:

  • Build a large dish farm Dish-Farm.jpg
  • Get a multi focus dish Toroidal.gif

Regardless of which of these you decide to persue, you'll need some way of getting all the signals from the various LNBs into your MythTV box. This is where a Multiswitch comes in.


EMP Centauri 154-AP

The EMP-154AP Multiswitch allows 4 receivers to switch between 8 LNBs. This is necessary to be able to tune to channels from different satellites. In New Zealand there are 8 satellites with beams pointed in useful directions

NewZealand Satellites.jpg.

The image below shows how this switch can be used to access all KU-Band satellites visible in the New Zealand sky.


Port Layout/Selection

The ports on the 154 are selected as follows:

  • Port A = DiSEqC A - No 22kHz Tone - 13V (Vertical Polarisation)
  • Port B = DiSEqC A - No 22kHz Tone - 18V (Horizontal Polarisation)
  • Port C = DiSEqC A - 22kHz Tone - 13V (Vertical Polarisation)
  • Port D = DiSEqC A - 22kHz Tone - 18V (Horizontal Polarisation)
  • Port E = DiSEqC B - 22kHz Tone - 18V (Horizontal Polarisation)
  • Port F = DiSEqC B - 22kHz Tone - 13V (Vertical Polarisation)
  • Port G = DiSEqC B - No 22kHz Tone - 18V (Horizontal Polarisation)
  • Port H = DiSEqC B - No 22kHz Tone - 13V (Vertical Polarisation)

So you can see that we are going to need to control the DiSEqC 1.0 switch, the 22kHz Tone and the voltage (polarisation) to select which LNB we want to receive from.

DiSEqC Tree

Myth builds this sort of switching mechanism using a tree structure under the Card Input section of mythtv-setup. Where you would normally configure a simple LNB, we are going to configure much more. Here is how the DiSEqC tree should look. Notice that there are only 4 LNB's configured. This is because the H/V ports on the switch make two LNBs look like a single one.


As you can see we have 3 levels of switching here. The top level is a DiSEqC switch, the second level are Tone switches and the final levels are LNBs which will perform the voltage switching.

DiSEqC Switch

This top level handles switching between the 2 groups of 4 ports on the switch. These groups are labled SatA and SatB and you switch between them using DiSEqC 1.0 commands. The configuration screen looks like this.


Tone Switches

The next level uses Tone (22kHz) switches to switch between paris of the remaining 4 ports. The two tone switches are configured as follows.

ToneA ToneB

LNB Configuration

In a perfect world we would then be able to put the LNBs on the end of the switches and all would be good. I could never get this working, so I've come up with a bit of a hack. In order to ensure that the Tones are turned on for some LNBs and off for others, I have used the "Custom/Voltage&Tone" option to build the right configs.

All the LNBs are the same (standard 11300) with the exception of the ones on SatA-Tone which is a Universal Dual (10600). The configs are as follows.

SatA NoTone SatA Tone SatB NoTone SatB Tone

Video Sources

Now that we have all the physicals worked out in MythTV, we need to configure all the other sections in to integrate our setup into the system. First we'll configure some new Video Sources.

Configure a source for each of the LNBs you configured in the DiSEqC section (4 in all if you are using a full switch. I have 3 configured here.)


You can see from the image that I have 5 Video Sources:

  • Sky Digital (STB captured by PVR-500)
  • Optus D1 (Dual Universal LNB)
  • UHF (Captured by PVR-500)
  • Optus B3 - Optus C1 (Two LNBs, one on Vert and one on Horizontal)
  • PAS 8 - PAS 2 (Similar setup to above)

We need to set these multiple sources as each of these will control the switching tree at a later stage. Because I populate my program data manually (roll my own scripts), I don't actually have any grabber data defined. Here is an example from the Optus B3 - Optus C1 source.


Input Connections

Ok - So now we have a complicated switch setup (DiSEqC Tree), and some places to put channel and program data (Video Sources), we are now at the stage of linking these together. It is at this stage that we tell the switch setup how to configure itself for each of the Video Sources. Lets start by seeing what the Input Connections screen should look like.


You can see that there are 3 connections for the DVB card. You will need to create each of these in turn, selecting "New Input" each time. You can see here two examples of these connections.


Device Configuration Screens

This is where the magic happens. Now that we have a connection from a Video Source to a Capture card, we need to tell the switch how to behave for each one. The switch needs to know which DiSEqC and Tone settings to use for each Video Source. On the Input Connection screens above you seill see a DVB-S button. Clicking on that will present you with the "Device Configuration" screen like the examples below:


On these screens you will configure the switch to access the different LNBs.


To Come