A tunable delay line is calibrated to maintain the delay of the delay line at a desired value or within a desired range of values. In some aspects a signal is passed through a delay line multiple times so that the cumulative delay of the signal through the delay line (e.g., as indicated by a count) may be calculated over a period of time. The count is compared with an expected count and, based on this comparison, the delay of the delay line is adjusted as necessary. In some aspects the signal may comprise a digital signal. In some aspects a delay through a delay line may be calculated based on analysis of amplitude changes in a signal caused by a phase shift imparted on the signal by the delay line. In some aspects a delay line is incorporated into a transmitted reference system to generate and/or process transmitted reference signals.
