secstat and you:
Below -2 = no 1.0 systems
Below -2.5 = no .9 systems
Below -3 = no .8 systems
Below -3.5 = no .7 systems
Below -4 = no .6 systems
Below -4.5 =

Angel - Explosive (Kine/Exp)
Amarr - Thermal (EM/Therm)
Blood Raiders - EM (Em/Therm)
Caldari - Thermal (Kine/Therm)
CONCORD - Thermal (All)
Gallente - Thermal (Kine/Therm)
Guristas - Kinetic (Kine/Therm)
Khanid - Thermal (EM/Therm)
Mimintar - Thermal (Therm/Exp)
Mercenary - Thermal (EM/Therm/Kine)
Mordus - Kinetic (Kine/Therm)
Odamian - All (Kine/Therm)
Drones - EM (All)
Rogue Pirates - All (EM/Exp/Kine)
Sansha - EM (EM/Therm)
Serpentis - Thermal (Kine/Therm)
Zazzmatazz - Thermal (All)

Stacking Effectiveness:
1st mod: c(1) = 100,00% effectiveness
2nd mod: c(2) = 86,91% effectiveness
3rd mod: c(3) = 57,06% effectiveness
4th mod: c(4) = 28,30% effectivenes

Red jammers jam Minmatar ships
Yellow jam Amarr ships
Dark blue jam Caldari ships
Cyan/green jam Gallente ships