This is a sole-source solicitation for firmware upgrades to proprietary FEI-Zyfer, Inc. equipment for the Time and Frequency Reference Measurement System at the United States Naval Observatory. The contract will be a Firm-Fixed-Price Purchase Order awarded by NAVSUP FLC Norfolk. The anticipated award date is no later than June 30, 2026. The performance location is the United States Naval Observatory. No budget amount is specified.