I was just testing Air Unit antenna connection and if I disconnect the antenna by USB plug I almost loose completely signal.  I found out the antenna doesn't do anything by sd card.  Is it normal behavior?  

Steps to troubleshoot:
1. I swapped out the antenna and both of them work fine by the USB plug.
2. Both antennas do not work by the sd card unless by USB plug antenna is connected.
3. Goggles set to 700mv.

Any suggestions?  It is a new unit but it's past retail return policy.  

Im not sure if one antenna is an RX and one is a TX?  Were you having picture problems or range issues prior to this?   

I'm new to DJI FPV system.  It's Ifligt Titan DC5.  Only 2 flights.  The farthest I flew around 400ft in line of sight and signal were jumping between 3 and 4.  

That's pretty normal.  If it was going below 2 bars at that range I'd think that was strange.