Re: LF: DCF39

[MarkusVester@aol.com]

Dear LF group,

stimulated by Jim's observation of DCF-39 outages, I set up SpecLab's plotter to monitor the 138.83 kHz carrier from Sunday afternoon till tonight.

The two dark blue traces show the maximum and mininimum amplitudes within each two minute measurement interval. The usual 3 mV/m carrier, attenuated at the passband edge, places the upper trace at about 40% relative magnitude. The minimum trace reflects the energy spread during the short telegrams, about -8dBc when smeared by 0.34 Hz resolution bandwidth.

On Sunday afternoon, I aurally observed many short interruptions, where the carrier went off completely after a telegram, and ramped back up after a couple of seconds. These appear as dips to zero in the minimum trace. There was also a long outage between 12:00 and 14:15.

Another interesting feature is the apparent power switching. These 3 dB steps were again accompanied by short breaks, and occured at 20:40 (up), Monday 5:40 (down), 7:40 (up), 8:50 (down), 9:10 (up), 9:35 (down).

The light blue trace shows the recorded azimut, which should of course be constant and due north. The irregular nighttime variations are usually introduced by ionospheric multipath.

However the slower daytime deviations (300 to 350 degrees) are an artifact due to E-field antenna detuning by moisture. This "summer antenna" is a just piece of wire strung among the branches of a fir tree, and series resonated with about 10 mH. Whenever it starts to rain (which was often, e.g. at 16:05), its phase is retarded and the apparent azimuth deviates clockwise, letting the SXV trace on my grabber display turn from orange to greenish (makes sense doesn't it ;-) I have tried to minimize this by loading the antenna with a high receiver input impedance, but there is probably also a direct dielectric effect disturbing the local electric field.

The red traces and dots are for SXV around 135.75 kHz. They show the usual morning and afternoon fieldstrength minima, as well as the same weather artifacts in azimuth.

73 and best wishes
Markus, DF6NM