epersson - I'm not Todd but I think I can answer your first two questions, the last one will have to wait for someone else or Todd himself to answer.
Regarding BW - this is for the channel bandwith just before being demodulated. You can think of it like the IF bandwidth in a normal superhet receiver which affects the adjacent and alternate channel rejection (like "selectivity"). It's done using a "switched capacitor" filter (I'll let you Google that as it would take too long to explain here). Allowing you to choose gives you flexibility to experiment to determine what works best so as to reject interfering signals (near in-band, generally adjacent to the desired) without causing distortion in the desired signal. Because any regular filter, and especially a switch cap type, will have "irregularities" in it's passband response and rejection filter skirts (how symmetrical it is) it's good to make it adjustable for the user. This can vary from unit-to-unit as well so, even on the same system, your settings might not work exactly for another P25RX user. Hence the "playing around to find what works for you best" bit. If you don't have much or any adjacent channel issues the defaults may be fine. Digital modulated signals are much more "picky" when it comes to final IF filter quality so, unless you actually have near channel interferer issues, it is often best to use a wider setting as, unless it is a very high quality filter with precisely maintained characteristics like (ripple, time delay, etc.) making it very narrow, even though "in theory" it is set to handle the bandwidth of the channel and modulation involved, usually makes the non-ideal characteristics more problimatic (more bad or incorrectly determined "bits").
As for the clock frequency setting - I actually think this may help Cheeseburgers question too. The setting in the config screen will change the clock frequency after being written and the unit is power cycled. However, when you close and reopen the config SW the config screen will always default to what ever Todd has set the default to (it was at "400 MHz" in the version I last used but he my have changed it later) but that does not mean that the unit itself will change back to the default! You need to send the "mcu_speed" line command to the unit to get the actual speed it is running at so you should see what you set it to before. I have requested that Todd actually update the config window to reflect the actual clock speed the unit is operating at (in other words, automatically send that command querying the unit for what its clock speed is set at) at the time the config software is started in order to avoid user confusion. He may add this in the future just low on his list right now.
As to the "Y" vs. "V" distinction - this is the reason he added the ability to change the clock speed and the reason it is now set to a lower frequency than it used to be. The supply of parts has been reduced laterly (a problem for all, really) so, apparently, the mcu chip that he has always built the P25RX around, has been comming to him in a lower maximum clock speed variant. It used to have a maximum of 480 MHz but the parts that he has been able to obtain now only specify a maximum of 400 MHz. Since all of his timing in the software and firmware had previously depended on the 480 MHz clock setting he had to go in and rewrite some parts to handle the lower 400 MHz setting in order to accomodate newer built hardware that is only specified at the lower setting. But, just because the specification states a maximum of 400 MHz does not neccessarily mean that it won't work at higher rates BUT it may have unpredictable results batch-to-batch so he made the settings adjustable for the user. For "V" variants which use the older specified to 480 MHz max mcu's you leave it set for 480 MHz but you might want to set it lower just in case something in newer versions of software and firmware might be (unintentionaly) sensitive to the clock ferquency (which would be a "bug" that Todd would likely find and fix at some point) temporarily until the issue in the software is corrected. "Y" variants, I belive unless I have it backwards, use the newer "slower" mcu part so should be set at 400MHz or maybe 408MHz (another issue came up not too long ago having something to do with the audio, as I recall, that may not be easily solvable when operating at 400 MHz so a compromise lower limit of 408 MHz was selected as the "new" default.
Hope that answers your first two questions. The last one I cannot answer, sorry.
-Mike
