LF: DCF42/49 IM reduced

[MarkusVester@aol.com]

Hi group,

this morning I logged a significant reduction in the DCF42/DCF49 intermodulation products at 135.360 (with FSK bursts around 136.040) and 136.5475 kHz. Supported by similar observations in 2001 and 2002,  this is apparently caused by a seasonal antenna retuning at the Mainflingen site.

For two minutes around 7:22 UT, at least one TX was switched off and the IMPs completely disappeared, coming back at a lower level. Within the next 40 minutes, 136.547 showed some fiddling and finally ended up at its "summer level", 9dB below the previous value.

         135.36/136.04kHz     136.5475 kHz
  UT    dBµV/m  EMRP      dBµV/m EMRP
<7:20    ~30     600mW      +1.5    0.8mW
  7:23      25                        -3   
>8:14      25     180mW       -7.5    0.1mW

As the IMP also contains a broadband noise component from DCF42's modulation, LowFers in the Frankfurt region will hopefully benefit from its reduction as well.

There are four other unexplained lines which seem to originate from the same area:
 137580.2 Hz (continuous), 
 137161.8 Hz (short FSK bursts every 1.2s),
 136680.5 Hz (FSK every ~34s, similar but not related to DCF49 or DCF39 telegrams),
 136201.2 Hz (cont.),
all around -1dBµV/m here. None of these was affected by the maintenance.

73 es best wishes
Markus, DF6NM