External power needed to transmit?

I am having trouble getting my LimeSDR usb working as a transmitter in the 2.4GHz range, and I was wondering if part of my problem might be because I have not attached it to any external power supply. I have just tried running it on usb 3.0 and 2.0 power, and do not want to waste money on a power supply if unnecessary.

As many have found, using anything over 9VDC for external power can pop the “USB/EXT power switching chip”. Stay low on the voltage.
Otherwise, get a QUALITY USB3.0 hub. NOT one with a 5VDC wall wart, you want a 12VDC powered one.
I have not been able to draw more than 750ma through the hub & all works fine.