Get the full set of Lovett Williams CDs. Listen, mimic & compare by recording with your cell phone. A trick for instant playback is to use a second phone connected to a bluetooth speaker set across the yard. There will be a slight delay before the speaker plays back to you.
But, really, just listen to a recording of a live bird and practice matching it. If you use a pot call, check out Sadler McGraw's youtube videos.
trying to figure out Rio gobbler and javelina hunts in TX