From EVE Wiki, for Posterity 
Countering ECM
Now you should understand exactly what ECM is and how it works within Eve. How is it countered? In order to make it harder for ECM modules to jam you you simply need to increase your sensor strength. You can do this in a variety of ways:
- Get a bigger ship. Bigger, more powerful ships have naturally larger sensor strength: e.g a Merlin (frigate) has a sensor strength of 11 while a Raven (battleship) has a sensor strength of 22.
- Sensor Booster modules (mid slot) - These can be loaded with ECCM scripts to increase the strength against jamming. As active modules, they can also be overheated - and will normally overheat for quite some time.
- Signal Amplifiers (low slot) - These modules are similar to Sensor Booster modules but use low slots and give smaller bonuses.
- Remote Sensor Boosters - These allow you to remotely project ECCM script support on to your friend’s ship.
- Gravimetric / Magnetometric / Radar / Ladar Sensor Compensation skills - Increase sensor strength by 4% per level of their respective sensor types.