Your first task, should you choose to accept it (just saw MI4 in a theatre last night), is to get your PC and scanner talking to one another. You will need a USB-serial converter to accomplish this. Fortunately there are many off the shelf solutions that will work
No matter what software you use, you really need to understand how Dyamic Memory Architecture (DMA) works so you can comprehend how and why something is to be set up the way it is. Don't even think of trying to use the Uniden supplied manual - it's junk. A much better choice would be to go and get the Easier to Read manual for the 346XT from here (you can also order a printed version from Scanner Master)
There is also an extensive FAQ on the subject of DMA and the Uniden scanners.
The software itself is fairly well documented in the RadioReference wiki. You can get to the user guide via HELP/ONLINE HELP from FreeScan, or go to it directly. There are whole sections devoted to downloading data from RadioReference, both for conventional and trunked systems.
All the links for these things can be accessed from the list that's found at the bottom of the FreeScan home page.
You might also see if someone will send you a file - keep in mind that FreeScan will import Butel or UASD (Uniden Advanced System Director) files as sources. There is a Manitoba based Yahoo scanning group - that might be your best bet to find something local...
http://groups.yahoo.com/group/MB-Scanners/There really isn't a step by step guide anywhere - DMA is very flexible, but that also adds complexity to the process.
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Best Regards and GL Mike