What is HF Fax (High Frequency Fax / Radiofax)? Fax Authority > Glossary > What is HF Fax (High Frequency Fax / Radiofax)? LAST UPDATE: February 19th, 2019 For HF Fax, please see the entry on Radiofax. HF Fax (or High-Frequency Fax) is another term for Radiofax, and the terms can be used relatively interchangeably.