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Dick Rollema wrote:
<blockquote TYPE=CITE><b><font size=+0>Dear Walter & the LF-Group,</font></b>
<p><b><font size=+0>Today I tried to measure the field strength of Donebach
at 153kHz again.</font></b>
<p><b><font size=+0>I am pretty sure Donebach uses some form of controlled
carrier modulation, apart from the phase modulation mentioned by Walter.</font></b>
<p><b><font size=+0>Our Dutch MF transmittters at 747kHz and 1008kHz are
also made by Telefunken (400kW at daytime). The 747kHz transmitter
uses controlled carrier to save power and expenses; the 1008kHz one does
not. The carrier at 747kHz, as measured by the SPM-12 at 25Hz bandwidth,
shows the same kind of fluctuations as the Donebach one, the 1008kHz carrier
is steady.</font></b>
<p><b><font size=+0>Remarkable is Droitwich at 198kHz. There the carrier
goes downward during modulation!</font></b>
<p><b><font size=+0>The varying carrier strength of Donebach makes it difficult
to read the meter of the SPM-12. But the instrument has at the back a "DC
output" that is proportional to the measured value (so it is not
DC a purist will remark). I fed that voltage to an oscilloscope and noted
the maximum deflection, which also cannot be read accurately because
of the wild jumps of the deflection with the modulation. I then replaced
the loop aerial by a HP606B signal generator, tuned it to 153kHz and adjusted
the output to the same deflection. The generator voltage was then 20 microvolt.
With a 1 x 1m single turn untuned loop this means the field strength of
Donebach is 6.25 microvolt/m. Using the CCIR groundwave curve for "Land"
(conductivity 30mS/m; dielectric constant 40) the power of Donebach follows
as </font></b><font size=+1>200kW EMRP</font><font size=+0>.</font>
<br><font size=+0>The aerial efficiency is given by Walter as 88%.
This indicates a transmitter power of 200/0.88 =
</font><font size=+1>227kW.</font>
<br><font size=+0>Perhaps, as suggested by Walter, there is only one 250kW
transmitter in operation. What with the uncertainties involved and the
fact the aerial system is not omnidirectional the 200kw EMRP looks to me
like a plausible result, taking into account the uncertainties involved
in the process.</font>
<p><font size=+0>As a check I inserted in G4GFQ's groundwave propagation
computer program P = 227kW, efficiency of the transmit aerial 88%,
pastoral ground (number 5) and distance 435km. The field strength came
out as 5.33 microvolt/m, which differs 1.4dB with my measured value.</font>
<p><font size=+0>73, Dick, PA0SE</font>
<br>
<p><font size=+0>At 09:10 28-7-02 +0200, you wrote:</font>
<blockquote type=cite class=cite cite><font size=-1>Dick, what I forgot
yesterday - the efficiency of the Donebach-antenna is quoted as 88% for
153KHz.</font>
<br><font size=-1>73 Walter</font>
<br>
<dl>
<dd>
<font size=+0>-----Ursprüngliche Nachricht-----</font></dd>
<dd>
<font size=+0>Von: <a href="mailto:walter.staubach@fen-net.de">Walter</a></font></dd>
<dd>
<font size=+0>An:
<a href="mailto:rsgb_lf_group@blacksheep.org">rsgb_lf_group@blacksheep.org</a></font></dd>
<dd>
<font size=+0>Gesendet: Samstag, 27. Juli 2002 18:06</font></dd>
<dd>
<font size=+0>Betreff: LF: Re: Power of Donebach 153kHz TX</font></dd>
<br>
<dd>
<font size=-1>Dear Dick and All,</font></dd>
<dd>
<font size=-1> about DLF. During daylight time normal
transmitting power is 500KW from 2 transmitters by Telefunken, each 250KW.
These power is fed to the northwestern one of the two masts. The southeastern
one is coupled by radiation and has a phase shift. This generates a 3dB
attenuation to southeast - because of Radio Brasov, Romania, on the same
frequency. During the night power is reduced to 250KW, fed to both masts,
also with phase shift. So the attenuation increases to 11dB to protect
the Brasov-area. I think you get the full radiation. But probably today
is only one transmitter in use because of maintenance. Please try next
week again. BTW: The carrier is also modulated in phase shift with GPS-correction-data.</font></dd>
<dd>
<font size=-1>73 Walter DJ2LF</font><font size=+0></font></dd>
<dd>
<font size=+0> </font></dd>
<dd>
<font size=+0> </font></dd>
<dd>
<font size=+0> </font></dd>
<dd>
<font size=+0>-----Ursprüngliche Nachricht-----</font></dd>
<dd>
<font size=+0>Von: <a href="mailto:d.w.rollema@freeler.nl">Dick Rollema</a></font></dd>
<dd>
<font size=+0>An: <a href="mailto:rsgb_lf_group@blacksheep.org">LF-Group</a></font></dd>
<dd>
<font size=+0>Gesendet: Samstag, 27. Juli 2002 11:03</font></dd>
<dd>
<font size=+0>Betreff: LF: Power of Donebach 153kHz TX</font></dd>
<dd>
<font size=+0>To All from PA0SE,</font></dd>
<dd>
<font size=+0>Sorry to bother you again with a field strength story. But
the delete key is within easy reach...</font></dd>
<br>
<dd>
<font size=+0>The Deutschlandfunk Donebach transmitter at 153kHz is on
again. At 0840 UTC today I measured its field strength as 5.6millivolt/metre.</font></dd>
<dd>
<font size=+0>Using the CCIR groundwave propagation curve that produces
plausible results on DCF39 and M0BMU the Effective Monopole Radiated Power
(EMRP) comes out as 157kW.</font></dd>
<br>
<dd>
<font size=+0>On the Internet I found transmitter power is 500kW. But there
are two 363m high aerial masts. This suggests a directive array. As the
transmissions are probably not meant for the Netherlands we may get only
part of the full blast.</font></dd>
<br>
<dd>
<font size=+0>Measuring with the SPM-12 in 25Hz bandwidth the reading moved
up and down a bit with the modulation. Perhaps some power (and money) saving
controlled carrier system is used. It could also be that some of the lowest
modulation frequency components are passed by the 25Hz I.F. filter.
But other BC stations on LF do not show the effect.</font></dd>
<br>
<dd>
<font size=+0>73, Dick, PA0SE</font></dd>
</dl>
</blockquote>
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