Re: LF: noise level on 137kHz

[MarkusVester@aol.com]

Dear Hartmut and LF,

yes, I can confirm your observation. The violet (northerly) noise can be found in the stored grabber screenshots, which I uploaded again at
http://members.aol.com/df6nm2/test0503141400.gif (291kB) and
http://members.aol.com/df6nm2/test0503141420.gif (318kB) ;
you may have to increase the display brightness or gamma to actually see the background.

After a very strong and short peak at 13:53, the noise changed several times at lower levels after 14:00. An a-posteriori evaluation from the calibrated captures within an otherwise empty part of the band resulted in the plot shown here. The arrows are associated with apparent changes in the suspected 177 kHz sidebands, possibly related to tuning activity at the TX site. The level increased from a relatively quiet background of ~ -23 dBµV/m /sqrt(Hz) by about 6 to 10 dB. There may be a little uncertainty due to the 256-colour mapping in the stored gif images, but the RMS averages should be good to within a couple of dB.

Given the groundwave distance of 380 km between Berlin and Nuernberg, this would result in a radiated power density of approximately
-13  - 79.5 + 20 * log (380) + 0.02 * 380  dBW/Hz = -33.3 dBW/Hz,
equivalent to 0.47 W/kHz or - 60 dBc/kHz, at 40 kHz (!) from the carrier. This is roughly the same sideband level that the 153 kHz DLF transmitter had at the time of its infamous modulator fault. I am not sure whether 177 kHz is currently being operated in the compatible "simulcast" mode, which transmits analog and digital modulation at the same time, and what effect this would have on the spectral envelope.

These interference levels are potentially quite threatening to any weak-signal work on LF. What makes it even more alarming is that unlike analog AM with its relatively low average modulation index, DRM sidebands are continuously at 100% density. Unless radiated powers would be decreased by an order of magnitude, the migration to digital will also be likely to change the character of nightly Luxembourg effect in a nasty way.

So let's make good use of this wonderful band it while it is still usable :-(

Regards
de Markus, DF6NM


In einer eMail vom 14.03.2005 16:58:43 Westeuropäische Normalzeit schreibt wolff.h@t-online.de:

Today I noted a higher noise level on 137kHz since 1353z. This
increase of noise could also be seen on the DF6NM grabber. Maybe this
is a result of the DRM transmission from the Deutschland Radio on
177kHz with 500kw.

73

Hartmut              mailto:wolff.h@t-online.de