Note that the red trace continues after Pyongyang fades out. At the time that the green frequency trace jumps down about 3-5Hz or more another, unknown station has faded in, then switches off at 04.00. This may be Honduras. Not seen on all dates. On the lower charts I have separated these signals by carefully configuring SpecLab's text capture. It is shown by a blue trace.
This technique is only satisfactory if the frequencies are stable from day to day otherwise the charts will not be consistent as shown below!
Pyongyang November 2009