A multiswitch allows you to have more than 2 recievers to one dual LNB. The most comon ones are 2x4, 3x4, 3x8, 4x4, 4x8 etc
The 1st number is how many inputs. An odd number (3,5) means the 3rd is an OTA antenna. The 2nd number is outputs.
I knew about multiswitches with DirecTV but can also be used in a FTA application. Normally when you have a dual LNB and hook 2 receivers to the LNB, each reciever can get both polarities. But what if you want 3 receivers to one LNB? Sure you can split the one output to 2 boxes, but then they can't be on opposite polarities. The multiswitch allows 4 boxes to have both polarities.
You hook the 2 lines from the LNB to the switch. One is 13v (V) and one is 18v (H). Hook the receivers to it. So in essence, the multiswitch "forces" each output of the LNB to only have V or only have H. When you select a channel on the reciever that is H, the signal goes to the multiswitch and takes the 18v side. If you have another box on a vertical channel, the signal goes to the 13v side. So you could have all 4 boxes on a vertical channel, all 4 on a Horizontal, or a mix.
The 4x4 switches were used when DirecTV added 119. In a FTA application, think of a 4x4 as a giant 22k switch. You can hook 2 dual LNB's to it and select between 4 receivers. One LNB would be 22k off and one would be 22k on.
In the below picture are a couple of 4x4 multiswitches. The cables on the left are from 4 dual LNB's and the 4 on the right go to a couple diseqc switches. So each LNB would have both a diseqc port and 22k setting
1st LNB would be port 1 22k off
2nd LNB would be port 1 22k on
3rd LNB would be port 2 22k off
and so on