Oscillator frequency control loop based on long term average of frequency difference

An oscillator unit for a base station or the like in a digital cellular radio network, which oscillator unit comprises an oven stabilized crystal oscillator (21), characterized in that the oven stabilized crystal oscillator (21) is adjustable and that the oscillator unit further comprises

• a non-volatile memory means (27) for storing a control information substantially corresponding to the assigned frequency and defining the frequency of the oven stabilized crystal oscillator (21) at the start of the oscillator unit,
• a means (30, 31, 32) for deriving a reference frequency from a fixed digital transmission connection between the base station and the remaining cellular radio network, such as a PCM connection,
• a frequency control loop (21, 22, 23, 24) for maintaining a long-term stability for the oven stabilized crystal oscillator (21) on the basis of a long-term average of the difference between the frequency of the oven stabilized crystal oscillator and said reference frequency.