Here is a link to a procedure to be able to see your numeric signal strength in db. Lower is better. From 90-100 plus is marginal.It is possible that when you enter the field test, you get disconnected from a network extender if you are using it. Enjoy.
http://www.funkyspacemonkey.com/ena...th-iphone-5-iphone-5s-iphone-5c-running-ios-7
http://www.funkyspacemonkey.com/ena...th-iphone-5-iphone-5s-iphone-5c-running-ios-7