A few points:
1. HRD lists the FT-847 as a supported radio. So you should be OK, there -- the FT-847 _does_ support computer control (CAT).
3. If your computer has a serial port, you may need an adapter to converter the serial-port voltage levels to the FT-847 CAT levels. If your computer has a USB port, you can use the adapter cable you'll find when you search eBay for
. . . FT-847 CAT
4. If the SignaLink has a 6-pin "mini-DIN" plug, it will probably work on the FT-847 _if_ the FT-847 has a "data jack" with a 6--in mini-DIN socket.
5. Read this article -- you may need just DM780 (the HRD digital-modes program), not the full-blown HRD CAT package:http://www.eham.net/articles/23794