Batboard

I had gotten a board from a radio I picked up on ebay, so I was messing around in the codeplug, and noticed when the voice was set to ASTRO, the options for encryption were limited. Also I noticed that after switching the voice to non-astro, the would stay the same. I will probably not pursue encryption behind testing around becasue of the fact that I can't lock the radio and have encryption at the same time for some reason. So does anyone know why ASTRO voice would make a difference when it comes to secure options? I assume it wouldn't make a difference with trunking, since the voice is set in the talkgroup (after selecting astro capable I believe...)?