ECCM, short for Electronic Counter-Countermeasures is an additional mode that expands upon the use of ECM suites.
Any ECM suite can be set to ECCM mode to jam enemy ECM suites. The ECM suite in this mode loses its normal functions when used this way. While in ECCM mode, any enemy ECM transmissions within range will be neutralized. If multiple units are in an area with ECM and ECCM active, calculating which system rules out becomes complicated. This is because multiple ECM suites can counter enemy ECCM transmissions. One suite in ECCM mode counters one suite in ECM mode, and renders the intersecting area void of ECM (but not void of ECCM). Two intersecting ECM suites can overpower the ECCM transmissions, and render the intersecting area present with ECM transmissions.
- Maximum Tech, p 77