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| To: | "LF-Group" <[email protected]> |
|---|---|
| Subject: | LF: Calculating ERP from measured field strength |
| From: | "Dick Rollema" <[email protected]> |
| Date: | Sat, 20 Jul 2002 13:08:39 +0200 |
| Cc: | "g4fgq.regp-btinternet.com" <[email protected]>, "Jan Harte" <[email protected]>, "Jaap Kroon, PA0IF" <[email protected]>, "Klaas Robers, PA0KLS" <[email protected]> |
| Reply-to: | [email protected] |
| Sender: | <[email protected]> |
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To All from PA0SE Today at 0800 UTC I measured the field strength of Jim, M0BMU on 137.4kHz, at 11 microvolt/metre. The distance between M0BMU and PA0SE is 329km. Using the curves for ground wave propagation in CCIR recommendation 368-7 those for "Sea water, average salinity" (epsilon 70, conductivity 5S/m) and "Land" (epsilon 40, conductivity 30mS/m) produce the same result for Jim's ERP: 460mW (252mW EMRP) . Jim reported his ERP being 400mW (218mW EMRP); a difference of 0.6dB. Almost too good to be true! But when I apply the graph for "Land" to the signal from DCF 39 (distance 500km, field strength 2mV/m) I find an EMRP of 50kW and that is what is officially stated for its power. So that confirms the "Land" curve is pretty useful for distances and paths involved in my case. Reg Edwards, G4FGQ, has a free program called "Grndwav3" on his web site: www.btinternet.com/~g4fgq.regp/page3.html#S301. Entering Jim's EMRP=218mW and distance 329km the program predicts for the field strength at PA0SE the following: Sea water: 10.35 microvolt/m average: 8.18 microvolt/m pastoral: 9.50 microvolt/m. I measured 11 microvolt/m so Reg's program can also be used when the CCIR curves are not available. Warning: These methods only apply to ground wave propagation, so as long no sky wave is present. For distances up to a few hundred km this is true during daytime. 73, Dick, PA0SE |
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