When you want to have multiple receivers to be able to use the same dish and LNB, the thing to use is a multi-switch.
But before you can use a multi-switch, note there is a problem with the "polarity" (H/V) when using a SINGLE coax connection LNB.
You need to use a DUAL coax connection LNB. This is because the receiver applies 13 volts to the coax cable to get one polarity and 18 volts on the coax to get the other polarity.
You CAN'T have one receiver applying 13 volts to a single coax connection and the other receiver applying 18 volts at the same time!
The trick is to use a DUAL coax connection LNB. Then the multi-switch has two connections to the LNB. One connection is always 13 volts and one polarity, the other connection is always 18 volts and the other polarity (for use by the multi-switch). Then the multi-switch determines what polarity each receiver is wanting and connects the receiver to the appropriate connection on the LNB.
Need for dual coax connection LNB explained...
Technical Support for DSS Multiplexors, Fluke Multimeters, Progressive Tone Testers.
Multiswitch H/V problem explained...
http://www.hooktech.co.nz/pdf/Instal...i%20Switch.pdf
How multiswitches work (scroll 1/4 way down page)...
Part 1 - getting to know basics
3 x 4 multiswitch diagram
Dishkbron.com* installation diagram
Hooking up Multiple
Satellite Receivers...
HOOKING UP MULTIPLE SATELLITE RECEIVERS