[Lf] measuring radiation of Donebach 153kHz TX]

[Andre Kesteloot]

Dick Rollema wrote:

> Dear Walter & the LF-Group,
>
> Today I tried to measure the field strength of Donebach at 153kHz
> again.
>
> I am pretty sure Donebach uses some form of controlled carrier
> modulation, apart from the phase modulation mentioned by Walter.
>
> 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.
>
> Remarkable is Droitwich at 198kHz. There the carrier goes downward
> during modulation!
>
> 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 200kW EMRP.
> The aerial efficiency is given by  Walter as 88%.  This indicates a
> transmitter power of 200/0.88 = 227kW.
> 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.
>
> 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.
>
> 73, Dick, PA0SE
>
>
> At 09:10 28-7-02 +0200, you wrote:
>
>> Dick, what I forgot yesterday - the efficiency of the
>> Donebach-antenna is quoted as 88% for 153KHz.
>> 73 Walter
>>
>>
>>      -----Ursprüngliche Nachricht-----
>>      Von: Walter
>>      An: rsgb_lf_group at blacksheep.org
>>      Gesendet: Samstag, 27. Juli 2002 18:06
>>      Betreff: LF: Re: Power of Donebach 153kHz TX
>>
>>      Dear Dick and All,
>>          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.
>>      73 Walter DJ2LF
>>
>>
>>
>>      -----Ursprüngliche Nachricht-----
>>      Von: Dick Rollema
>>      An: LF-Group
>>      Gesendet: Samstag, 27. Juli 2002 11:03
>>      Betreff: LF: Power of Donebach 153kHz TX
>>      To All from PA0SE,
>>      Sorry to bother you again with a field strength story. But the
>>      delete key is within easy reach...
>>
>>      The Deutschlandfunk Donebach transmitter at 153kHz is on again.
>>      At 0840 UTC today I measured its field strength as
>>      5.6millivolt/metre.
>>      Using the CCIR groundwave propagation curve that produces
>>      plausible results on DCF39 and M0BMU the Effective Monopole
>>      Radiated Power (EMRP) comes out as 157kW.
>>
>>      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.
>>
>>      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.
>>
>>      73, Dick, PA0SE
>>



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