The 118 satellite is circular polarity and is a bit higher power than what 105 and 121 are.
But, I call B.S. on your 105 "switch." The only way to "switch the polarity," as you say, is to take apart the tiny feedhorn on the 105 LNBF and insert a dialectric plate and then carefully turn it to get the best signal. It will be very difficult to get a steady signal that would work in the rain by "switching the polarity" as you say.
You would rather buy a repoint kit from any number of online retailers which turns your SuperDiSH into a DiSH 1000+ equivalent that does a great job of holding a solid signal.
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