Very nice script 
, though personally I am not fond of the :while-do-delay approach in general and in this case I find that checking by this method two conditions (of which one is dependent on the other) is superfluous (though nice granularity for testing).
The USB 2 cable should work and it helps avoiding (not applicable to your case) 2.4 GHz interferences, JFYI:
http://forum.mikrotik.com/t/wifi-connection-deteriorated-with-usb-device-attached/172822/1