Is there a standard chart or directory for choosing the proper step ( 5.0 - 7.5 - 10 - 12.5- 15) .for the various mode applications, such as P25 - UHF - VHF FM - AM.
Doing some manual programming and looking for some guidance!
You seem to be confusing two issues. One item, which is "mode" (P25, DMR, Yaesu, etc) does not necessarily have to be relevant to "step size" (also known as "channel spacing"). This step size is more relevant to the operating band, which are groups of frequencies designated to be used by various services.
On the UHF ham band (420 - 450 MHz), the generally accepted step size, at least in the portion of the band that I listen to (440 - 450) is 12.5 KHz. Within this range, you will generally hear different modes of operation, such as narrow-band FM, P25, Yaesu digital Fusion, DMR, and D-Star.
If you move further up the band, into some of the "business band" swaths of frequencies (for example 480 - 512 MHz), you will encounter some of these mixed modes of operation in recently "split" channels. where the FCC has determined that radio operations will utilize channel steps of 6.25 MHz instead of 12.5 KHz, thereby doubling the number of available frequencies available. The FCC has given these operators a number of years to transition their equipment to accommodate this narrower channel spacing.
Channel spacing is not only critical in two-way radio operation, but to FM broadcast frequencies as well. In order to achieve the "fidelity" of FM radio for example, the spacing of channels is much wider since the size of each channel has a wider bandwidth in order to increase the fidelity. If you have the DV1, you will find that a wider bandwidth is required to monitor FM broadcast channels (either 100 or 200 KHz for example), as opposed to 15 KHz for your local police or fire channels.
I am generalizing to the "Nth" degree, just to give you an overview. You might try Googling "channel spacing" to start, and remember, these will vary depending on the counties involved. Each country generally sets standards for frequencies and/or bandwidths, although there are several telecommunications agencies which are set up under various charters (United Nations, for example) to help standardize these operating parameters around the world to help prevent interference.
Now that I have broached the subject, I hope others will contribute to the discussion.
