For accurate frequency calibration using Loran signals, see John Andrews' article on the LWCA web site at: http://www.lwca.org/library/articles/w1tag/R75cal.htm NDB frequencies are generally not accurate enough to use as calibration standards for QRSS work. At the moment, I measure ZWN (Winnipeg; 201.4 kHz) at about 6.4 Hz low, and YQ (305.4) is about 5.4 Hz high. Lyle, K0LR