Why A transverter is a frequency converter that sits between a transceiver and the antenna, mixing the radio's transmit output up (or down) to a different band and converting received signals on that band back to the radio's operating frequency. It contains a mixer and a local oscillator, plus a low-power transmit stage, so a 28 MHz HF radio can work 144 MHz or 1296 MHz. The name itself is a blend of transmit and converter, since it handles both directions.
Watch out High-pass and low-pass filters only block or pass ranges of frequencies, they cannot shift a signal to a new band; a filter changes what gets through, not where in the spectrum it lands.
Transverter = TRANSceiver + conVERTER: it moves both TX and RX to another band.