An update is being made to the Mendip transmitter, which serves the west of Swindon, together with much of Wiltshire, Bristol, Somerset and Gloucestershire.
Terrestrial-based TV services that use Freeview channels and will also be affected include YouView, BT TV, TalkTalk, EE and NOW TV.
The engineering work is part of signal changes that began in July 2017 and are set to continue until next year. Some airwaves currently used by Freeview are being reallocated to allow for the development of new mobile broadband services.
Freeview says some equipment will retune automatically but advised users with any concerns to visit www.freeview.co.uk or call 0808 100 0288 for advice.