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| To: | LF-Group <[email protected]> |
|---|---|
| Subject: | LF: SAQ on 24 Dec. 2007 |
| From: | Dick Rollema <[email protected]> |
| Date: | Mon, 24 Dec 2007 13:49:46 +0100 |
| Reply-to: | [email protected] |
| Sender: | [email protected] |
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Correction To All from PA0SE Today I had again good reception of SAQ on 17.2kHz. I used a Wandel & Goltermann SLM type SPM-12 connected to the aerial system for 136kHz with 26nF extra in parallel with the loading coil. Replacing the aerial by a one-turn untuned square loop of 1 x 1 m the signal was sufficiently over the noise to be measured at 0.155 microvolt (25Hz I.F. bandwidth). From this follows a field strength of about 429 microvolt/metre (52.6 dBµV). On June 30, 2002 I measured 482 microvolt/metre (53.6 dBµV) So the measurements are rather consistent. This makes it possible to do some speculation as to the power radiated by SAQ (Effective Monopole Radiated Power, EMRP). The coordinates of SAQ are given as 57.07N, 12.24E. Using a computer program written by Harry, PA0LQ, I find as QTH locator JO67CB. My own locator is JO22GD. Again using Harry's program yields a distance of 735km. We can now enter these data into the graphs of CCIR Recommendation 368-7 for ground-wave propagation. This results in: Type of ground dielectric constant conductivity (mS/m) EMRP Perfect ground - - 1.4kW Land 40 30 3.0kW Land 22 3 3.7kW Medium dry 15 1 4.7kW ground Dry ground 7 0.3 5.9kW ground If we estimate from these data an EMRP of 4kW then with an alternator output of 200kW the efficiency of the aerial system is (4/200) * 100% = 2%. This may not seem impressive but for an aerial at such a low frequency it is not too bad I think. The aerial system consists of six vertical radiators of 127 m high. They are fed in phase at the top and each radiator has its own loading coil and earth electrode (system also designed by Alexanderson) . The total horizontal length is 2200 m, which is only 0.13 wavelength. So the system may have been designed to give some gain in the wanted direction I cannot see how this could have been achieved. It would be nice if someone nearer to Grimeton would measure the field strength outside the near field area, for instance at 5 wavelength distance, or 87km. At that distance at 17.2km perfect ground can be assumed for calculating the EMRP (1kw produces 300mV/m at 1km distance, decreasing in a linear way with distance). 73, Dick, PA0SE |
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