Not a repeater but a micro-WWVB transmitter, [Anish]’s build consists of a GPS receiver module and an ultra low-power 60kHz transmitter based on an ATtiny44a microcontroller’s hardware PWM ...

The transmitter and receiver For the transmitter, he turned an Arduino Pro Micro into a USB sound card which he could plug into his laptop. That outputs both the audio signal and a 40 kHz carrier ...

Make: OT Systems Model code: NHD100Micro-SMT Transmitter Type: Yes No of Video Inputs: 1 channels Dimensions mm: 36.2 x 25 x 101 ...