OS X App Nap
App Nap - disable when running fldigi, flrig etal
App Nap is an energy feature introduced to the Mac in OS X Mavericks that causes inactive applications to go into a paused state, helping to reduce power usage. The feature can help to prolong battery life for the Mac Book, and it can also make an impact on overall energy usage from the computer. It can disable hardware i/o such as serial port, audio streams, socket services etc if it determines that the application is inactive.
Bad news for an application like fldigi, flrig, flamp, or any other that require those services. App Nap basically kills the application even though they may appear to be active to the casual user.
One indication is communication errors between Fldigi and Flrig which is indicated by a popup message of "Fldigi - Flrig Ptt Off Failure" or "Fldigi - Flrig Ptt On failure." This failure is often seemingly random.
If you are using a laptop with OS X disable App Nap for both Flrig and Fldigi and any other Fldigi suite application you are using that needs communication services. This is done in Finder by highlighting the icon and keystrokes CMD+I. Click the "Prevent App Nap" box.