3G Transmitters and Receivers have a null modem jumper on the bottom of the unit that flips the transmit and receive pins on the RS232 port.
The nature of RS232 is that there is always a 50% chance that you have the correct cable. By flipping the jumper, to the alternate position, you ALWAYS have the correct cable.
When using a Just Add Power Flux Capacitor IR Dongle (v1 or v2), the pins should ALWAYS be set to the Crossover position.
The null modem jumper on 3G devices is a 2x3 rectangle of pins. There are two valid positions for the null modem jumper, regardless of orientation:
One position is straight-through, one position is crossover. The orientation on the null modem jumper may be different on each device.
