The 2010 Manila revisions to the Seafarer Training Certification and Watchkeeping (STCW) Convention and Code brought in a Certificate of Competence (CoC) for Electro-Technical Officers (ETO).
If a particular ship is required to carry a Certified ETO, then by 1st January 2017 anyone signed on that ship as an ETO will need an STCW ETO CoC. If the ship is not required to carry an ETO, then the CoC remains optional.
Further details on all entry routes can be found in MCA document MSN 1860 (M) Training & Certification Guidance: UK Requirements For Electro-technical Officers.
To apply for your ETO CoC you are required to complete MCA form MSF 4259. The form is used by the MCA to establish your eligibility for the oral examination. If eligible, you will be issued with a Notice of Eligibility (NoE) enabling you to sit the oral examination. The form gives details of all qualifications you need to have in place prior to your oral, therefore a 'must read'. This overview of the CoC application and revalidation process is also very useful.
Reeds Vol 15: Electronics, Navigational Aids and Radio Theory for Electrotechnical Officers (Reeds Marine Engineering and Technology Series) by Steve Richards (12 Sep 2013). Publisher: Thomas Reed. ISBN-10: 1408176092 ISBN-13: 978-1408176092
Electronic Navigation Systems by Laurie Tetley and David Calcutt (20 Mar 2001)
3rd Edition. Routledge. ISBN-10: 0750651385 ISBN-13: 978-0750651387