Attached is a snapshot from the Twente WebSDR,
comparing the occupied bandwidth of the three telecontrol transmitters
DCF49, HGA22, and DCF39, which are operated by EFR http://www.efr.de/en. You can see that the
FSK modulation of the DCF39 transmitter is significantly wider than
the others, with sidebands going down to below 137 kHz.
This problem came up in April 2007 when a new
TransRadio http://www.transradio.de/ semiconductor
transmitter was installed in Burg. It has been exacerbated over the years
due to the introduction of long periods with a high
density of telegram bursts - we currently see about 50% modulation
activity during several one-hour periods per day. As the baud rate is only 200 bits per second, it would
certainly be technically possible to reduce the bandwidth by properly shaping
the transitions. If only someone could be bothered...
Best 73,
Markus (DF6NM)
|
Twente_DCF_telegrams_121230_1829_annotated.jpg
Description: JPEG image
|
