My apologies if this has been asked a million times before, but here goes:

My old RCA DirecTV receiver had an IR/RF remote, so even though the box was in the living room, I could change channels from the bedroom, where the 2nd TV was, on a split line. My new Sony DirecTV receiver has an IR only remote, so to watch the bedroom TV I had to hook up the RCA receiver, with DirecTV's $5/month fee. I live alone, so I really only need one receiver, but I do need to control it from the adjacent bedroom. I assume there is some sort of RF/IR interface I could purchase. Yes? If so, any recommendations?

You can get a remote extenders from RS, they're cheaper on ebay. You point your remote at the transmitter then it sends a RF signal to receiver that converts back to IR. They work great.

You can also get an IR/RF universal remote(OFA URC-9910, RS 15-2117[not yet released AFAIK but should be available any day now]) for $50 that puts out both a typical IR signal and an RF signal that's picked up by the receiver and converted back to IR as above. These are great because you can use them anywhere within up to 100 feet of the receiver (depending on building construction) - in the bathroom, the kitchen, wherever.