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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
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