do i need to cut JP1 if i am using an arduino board that is using external power?
Sparkfun recommends the following:
You will want an external power supply to run the module at full power . Please see the Power Supply Considerations section for more information.
Then Sparkfun goes on to state:
Target Power (Best)
Powering the SRTR over the 5V pin from an Arduino works well if the Arduino has an external power supply such as a 5V wall adapter. If the Arduino is powered only by USB the module will brown out under full read power. It’s important to note that the shield gets its power from the 5V pin which means it’s drawing power from the onboard regulator of whatever platform you are using. If you provide your RedBoard with 9V and draw 1A through the 5V regulator it will get red-hot. Use a 5V power adapter to reduce the thermal strain on your regulator.
From what I believe, Sparkfun writes here you would want to cut the jumper if you’re not powering it from a USB to Serial converter cable:
By default the JP1 Jumper is closed allowing the USB to Serial converter provide power to the SRTR. Cut this jumper if you are powering the board with a LiPo battery or other external power supply. This will isolate the USB to Serial converter for communication only.