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| To: | [email protected] |
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| Subject: | Re: LF: Re: Re: Power of Donebach 153kHz TX |
| From: | "Dick Rollema" <[email protected]> |
| Date: | Tue, 30 Jul 2002 12:37:37 +0200 |
| Reply-to: | [email protected] |
| Sender: | <[email protected]> |
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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. |
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