Over on YouTube Tech Minds has uploaded a new video where he shows how he can use his HackRF SDR with the SDRAngel software to easily transmit voice to a local ham radio repeater. If you are unfamiliar with ham radio, a ham repeater is simply a radio station that receives voice or other signals on a certain ham radio frequency, and re-transmits the signal with stronger power on another frequency. This allows communications to be receivable over a much larger distance.
SDRAngel is a very nice piece of SDR software that has controls for TX capable SDR's like the HackRF. In the video Tech Minds shows the HackRF being used as a transmitter, with it transmitting to a repeater at 145.137 MHz. An RTL-SDR is then used to listen to the repeater output at 145.737 MHz. With this set up he is able to contact a friend via the repeater easily.
It doesn't appear that Tech Minds is using any sort of external amplifier, so this shows that the HackRF is powerful enough to hit local repeaters just by itself.