If you are just trying to send/receive TTL signals, I would advise you to take a look at the the digital cards that we have: PCI 6533 or PCI 6534. The first one has a maximum sampling rate of approximately 76 Mbytes/s (Rates may depend on application, computer and software) and the second one has a maximum sampling rate of 80Mbytes/s (his one has Onboard Memory).
Now, we also have some RF switching modules like the SCXI 1190 and SCXI 1191 that might capture your interest. The 1190 is a 50 Ohms, 1.3 GHz Multiplexer Switch, and the 1191 is a 50 Ohms, 4GHz Multiplexer Switch. For PXI systems, the NI 2590 and the NI 2591 will be equivalent
For more information about this products it would be a good idea to go to http://www.ni.com/catalog/ an d do a search on these product. Good luck!