LF: DCF and HGA modulation spectra

["Markus Vester" <markusvester@aol.com>]

Dear LF,

 

the LF grabber capture at http://df6nm.bplaced.net/LF/test1012121515.jpg is a good example of the modulation spectra of HGA22 and DCF39.

 

At 15:04, I had deactivated the noise blanker, which is normally used to cut out most of the DCF39 modulation clicks. Thereafter, you can see the true spectral content of the FSK sidebands. The strong purple (ie. northerly) vertical lines intruding from the top are from DCF39 Magdeburg, and the red (ie. easterly) ones near the bottom are from HGA22 Budapest.

 

Between 15:05 and 15:12, there is a dense block of telegrams, which is transmitted from all "EFR" stations in near synchronism. The newer DCF39 transmitter (which was put to service in 2007) obviously has virtually unfiltered modulation, with keyclicks going down all the way to about 136.5 kHz. Below that, HGA22 takes over, with a somewhat narrower modulation but of course closer to the carrier. The two of them combined are covering up all of the LF band here.

 

The gaps in the red HGA spectrum are clearly visible, at all multiples of approx. 200 Hz from the active space frequency 135.77 kHz. There are blue dashes from "Z" (SM6BHZ?), fitting in nicely at 137.176 kHz. The different effect on proposed Eu slot frequencies can be seen on http://df6nm.bplaced.net/LF/testEu1012121515.jpg .

 

Interestingly, DCF39 is different in that there are actually two sets of gaps, spaced at 200 Hz intervals around both the mark and space frequency. This is probably due to a subtle difference  in the serial stop-bit timing between the transmitters. In effect, nulls are at at 137.765, 137.565, etc. kHz, and also at 137.83, 137.63, ... kHz. In the capture there are faint yellow dashes from OE5ODL at 137774.5, indicating that our TA slot allocation is actually just a tad too high to fit into a gap.

 

Best 73,

Markus (DF6NM)

 

 

From: Markus Vester

Sent: Sunday, December 12, 2010 3:13 PM

To: rsgb_lf_group@blacksheep.org

Subject: LF: New Eu slot 136.177 kHz?

...

Here in Europe and Russia, a possible disadvantage of going down is that we would also come closer to HGA22. This is the 100 kW telecontrol transmitter in Budapest, an idle carrier sitting at 135.43 kHz, and excursions to 135.77 during FSK bursts. Normally these bursts appear every 11 seconds, but at times there are annoying blocks of consecutive telegrams several minutes long. Here in Bavaria, the FSK modulation sidebands are visibe up to about 136.5 kHz, but there are pronounced spectral gaps due to the 200 bd modulation. These clear gaps are near 135.97, 136.17 and 136.37 kHz.

...