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To All from PA0SE

Yesterday I have measured the field strength of my LF transmitter at a distance of 5.83km; more than enough to be outside the near field that would disturb the measurement. The location was open countryside without buildings and streetlamps or other signs of buried cables that could distort the field.

Using an untuned single turn loop and a Wandel & Goltermann selective level meter type SPM-12, run off the car battery, I found a FS of 370 microvolt/metre. From this follows an impressive radiated power (EIRP) of 52 milliwatt.

I simulated the aerial system using computer program AO.

The impedance at the feed point of the arerial is given by the computer as Z = 0.045 - j3817 ohms.

Aerial current is 1.95A. This results in an EIRP of 1.95 * 1.95 * 0.045 W = 171 milliwatt.

Measured value was 52 milliwatt. Apparantly 5.2dB is lost due to radiation into the earth and absorption in surrounding objects of the aerial; a figure that has been reported by others as well.

I also measured the field strength of DCF139 in the countryside and found 2mV/m, the same value as in my shack.

I have sent this message before, but then extended with a photograph (40.7kB) and description of the aerial system. But this was apparantly rejected by the reflector; at least I did not receive in my own mailbox.

73, Dick, PA0SE