Direct EPR irradiation of a sample using a quartz oscillator operating at 250Â MHz for EPR measurements

► Direct EPR irradiation using a quartz oscillator operating at 250 MHz is performed. ► It is necessary to tune the EPR resonator to the quartz oscillator frequency. ► A single-turn coil with a varactor diode attached (frequency shift coil) is used. ► High sensitivity EPR measurements can be made at high irradiation power.