Originally Posted by n1das
D156N = D265I
D265N = D156I
D156N and D265N (and D156I and D265I) are inverses of each other. In general any radio that can do DCS can do inverted DCS. If you have a normal code you can look up its inverse in the table of standard DCS codes, and vice versa, i.e., if you have an inverted code you can look up its inverse as a normal code.
More info on DCS/DPL operation:
DPL / DCS Information
This is probably the best technical reference I've been able to find online.
Exactly. It's all how the receiver extracts the code. Some designs will invert the code. If this is the case, you'll have to hunt for the correct code in the normal table that is the inverse equivalent to make things work. Confusion for sure. Better to keep the same code number but use the inverse option for those radios that need it.
Sometimes the transmitter will invert the code. Putting a Comm-Spec DCS encoder on an old Micor compa comes to mind for some reason.
You won't see an inverse code used much because there is no advantage to it if it's not really needed. It is not a whole set of different codes to use, just the normal table kinda jumbled around.
Most all modern microprocessor controlled radios these days are on the same page and using the normal table for codes always works.