Received-SPF: neutral (google.com: 193.82.116.20 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org)
From: MarkusVester@aol.com
Message-ID: <c02.1296bc3d.33463a7a@aol.com>
Date: Thu, 5 Apr 2007 07:41:46 EDT
To: rsgb_lf_group@blacksheep.org
MIME-Version: 1.0
Subject: LF: More QRM from DLF and DCF39
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Reply-To: rsgb_lf_group@blacksheep.org
Status: O


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Dear LF,

after signon of Rugby Loran and Budapest, interference to the 137 kHz band i=
n=20
Central Europe has again become worse twice. This was apparently caused by=20
recent changes in the modulators of two large broadcast/utility stations, DL=
F=20
and DCF39.


DLF (Deutschlandfunk Donebach, now 250 kW on 153 kHz) has always been prone=20
to have a pair of spurs about 17 kHz from the main carrier, which are=20
FM-modulated across several kHz by the program content. They were quite stro=
ng (up to=20
-65 dBc) for some time in 2002/2003. Though the origin of the spurs is still=
=20
not understood, one on-site engineer found a workaround to mitigate the prob=
lem,=20
by placing a PCB in the 54 kHz switch-mode modulator circuitry on an extende=
r=20
board and thus cooling a certain CD4011 chip.

This year Feb 22, 9:20 the problem reappeared at somewhat lower level, first=
=20
intermittently but now permanent since Feb. 28. In an SSB receiver tuned to=20
136 kHz, the lower spur is audible as a shuffling and hissing sound, going o=
n=20
and off along with the modulation on 153 kHz - it actually sounds very much=20=
like=20
listening to a FM broadcast transmission in SSB mode. In my colour-DF=20
spectrograms, it shows up as a blue-greenish haze, interrupted by irregular=20=
short=20
pauses. The screenshot http://members.aol.com/df6nm2/QRM/DLF_break_070317.pn=
g was=20
taken during a short transmitter outage on Mar 17, and really shows the=20
impact on the receive situation on a quiet day.

At 160 km range, the spurious noise is -12 dB =B5V/m/sqrt(Hz), some 6 dB abo=
ve=20
my average daytime background. This corresponds to a sideband power density=20=
of=20
-72 dBc/kHz at the transmitter. There is also a weak (-93 dBc) line, slowly=20
drifting within about 10 Hz around 136.75 kHz.=20

I have contacted the Donebach staff and informed them about the reappearance=
=20
of problem. Unfortunately they said they can do nothing about it at the=20
moment. They have dismantled one of their two 250 kW units, and are currentl=
y in the=20
process of installing a new digital transmitter, which is scheduled to=20
transmit DRM and Simulcast (AM-compatible DRM) formats after June 2007. This=
=20
statement however did raise even more concerns from Eike (DJ5AO) and myself,=
=20
regarding potentially drastically higher noise sidebands from digital transm=
issions.


The other new problem is caused by DCF39 (Burg, 40 kW, 138.83 kHz idle with=20
FSK telegrams every 10 seconds). Normally at 310 km range, the FSK sidebands=
=20
were just barely visible below 137.8 kHz in daylight. Since April 2nd, 08:55=
,=20
the bursts seem to have increased amplitude and are extending all the way do=
wn=20
to 137.1 kHz! This is probably related to the idle frequency change (normall=
y=20
138830.03Hz, now 0.4 to 0.57 Hz high), reported by several LF observers.=20

The transmitter switched back and forth between "narrow" and "wide" modes a=20
couple of times yesterday, and has been "wide" continuously since April 4,=20
13:00 UT. For a comparison, please look at=20
http://members.aol.com/df6nm2/QRM/DCF39_sidebands_070404.png - even with the=
 rather inconspicuous violet rendering=20
you can see the significant effect on the QRSS slots around 137.7 and 137.78=
=20
kHz.

My unconfirmed assumption is that the modulation parameters of DCF39 have=20
been changed towards even less pulse shaping. But an occupied bandwidth of 3=
.8=20
kHz for a 200 bd FSK signal would seem rather ridiculous! I would be keen to=
=20
know whether others are also seeing the annoying sidebands, and if anyone in=
 the=20
group has contact information to the DCF transmitter operators on site.=20


73 and Happy Easter,
Markus, DF6NM
  =20

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Content-Type: text/html; charset="ISO-8859-1"
Content-Transfer-Encoding: quoted-printable

<HTML><FONT FACE=3Darial,helvetica><HTML><FONT  SIZE=3D2 PTSIZE=3D10 FAMILY=
=3D"SANSSERIF" FACE=3D"Arial" LANG=3D"2">Dear LF,<BR>
<BR>
after signon of Rugby Loran and Budapest, interference to the 137 kHz band i=
n Central Europe has again become worse twice. This was apparently caused by=
 recent changes in the modulators of two large broadcast/utility stations, D=
LF and DCF39.<BR>
<BR>
<BR>
DLF (Deutschlandfunk Donebach, now 250 kW on 153 kHz) has always been prone=20=
to have a pair of spurs about 17 kHz from the main carrier, which are FM-mod=
ulated across several kHz by the program content. They were quite strong (up=
 to -65 dBc) for some time in 2002/2003. Though the origin of the spurs is s=
till not understood, one on-site engineer found a workaround to mitigate the=
 problem, by placing a PCB in the 54 kHz switch-mode modulator circuitry on=20=
an extender board and thus cooling a certain CD4011 chip.<BR>
<BR>
This year Feb 22, 9:20 the problem reappeared at somewhat lower level, first=
 intermittently but now permanent since Feb. 28. In an SSB receiver tuned to=
 136 kHz, the lower spur is audible as a shuffling and hissing sound, going=20=
on and off along with the modulation on 153 kHz - it actually sounds very mu=
ch like listening to a FM broadcast transmission in SSB mode. In my colour-D=
F spectrograms, it shows up as a blue-greenish haze, interrupted by irregula=
r short pauses. The screenshot <A HREF=3D"http://members.aol.com/df6nm2/QRM/=
DLF_break_070317.png">http://members.aol.com/df6nm2/QRM/DLF_break_070317.png=
</A> was taken during a short transmitter outage on Mar 17, and really shows=
 the impact on the receive situation on a quiet day.<BR>
<BR>
At 160 km range, the spurious noise is -12 dB =B5V/m/sqrt(Hz), some 6 dB abo=
ve my average daytime background. This corresponds to a sideband power densi=
ty of -72 dBc/kHz at the transmitter. There is also a weak (-93 dBc) line, s=
lowly drifting within about 10 Hz around 136.75 kHz. <BR>
<BR>
I have contacted the Donebach staff and informed them about the reappearance=
 of problem. Unfortunately they said they can do nothing about it at the mom=
ent. They have dismantled one of their two 250 kW units, and are currently i=
n the process of installing a new digital transmitter, which is scheduled to=
 transmit DRM and Simulcast (AM-compatible DRM) formats after June 2007. Thi=
s statement however did raise even more concerns from Eike (DJ5AO) and mysel=
f, regarding potentially drastically higher noise sidebands from digital tra=
nsmissions.<BR>
<BR>
<BR>
The other new problem is caused by DCF39 (Burg, 40 kW, 138.83 kHz idle with=20=
FSK telegrams every 10 seconds). Normally at 310 km range, the FSK sidebands=
 were just barely visible below 137.8 kHz in daylight. Since April 2nd, 08:5=
5, the bursts seem to have increased amplitude and are extending all the way=
 down to 137.1 kHz! This is probably related to the idle frequency change (n=
ormally 138830.03Hz, now 0.4 to 0.57 Hz high), reported by several LF observ=
ers. <BR>
<BR>
The transmitter switched back and forth between "narrow" and "wide" modes a=20=
couple of times yesterday, and has been "wide" continuously since April 4, 1=
3:00 UT. For a comparison, please look at <A HREF=3D"http://members.aol.com/=
df6nm2/QRM/DCF39_sidebands_070404.png">http://members.aol.com/df6nm2/QRM/DCF=
39_sidebands_070404.png</A> - even with the rather inconspicuous violet rend=
ering you can see the significant effect on the QRSS slots around 137.7 and=20=
137.78 kHz.<BR>
<BR>
My unconfirmed assumption is that the modulation parameters of DCF39 have be=
en changed towards even less pulse shaping. But an occupied bandwidth of 3.8=
 kHz for a 200 bd FSK signal would seem rather ridiculous! I would be keen t=
o know whether others are also seeing the annoying sidebands, and if anyone=20=
in the group has contact information to the DCF transmitter operators on sit=
e. <BR>
<BR>
<BR>
73 and Happy Easter,<BR>
Markus, DF6NM<BR>
</FONT>   </HTML>

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