CFR › Title 47 › Part 87 › §87.7147 CFR §87.71Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗Copy linkA licensed operator must measure the operating frequencies of all land-based transmitters at the following times:(a)When the transmitter is originally installed;(b)When any change or adjustment is made in the transmitter which may affect an operating frequency; or(c)When an operating frequency has shifted beyond tolerance.