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Re: LF: GW F-s versus Wx parametres

To: [email protected]
Subject: Re: LF: GW F-s versus Wx parametres
From: [email protected]
Date: Fri, 24 Mar 2000 11:33:00 EST
Reply-to: [email protected]
Sender: <[email protected]>
As a broadcast engineer, I have had opportunities to observe apparent ground conductivity changes with temperature, and over at least some types of soil, there does appear to be a fairly decent correlation (if not exactly huge, under temperate conditions) at mediumwave. The "Influence of Atmospheric Humidity on Low-Frequency Radio Ground Waves" article, however, is one which caused a bit of a fuss when it first appeared over here in The LOWDOWN. It invokes a new cause, without any hypothesis for a working mechanism, for an effect that is already quite easy to explain. One might note that some of the numbers in the article have pre-corrections applied that involve precisely the variables whose effects are supposedly being demonstrated. Of course a "correlation" will be found when one does that! Furthermore, the atmospheric humidity values are not known over the paths to the different stations whose signals are being measured...only near the receiving site. It is not valid to assume the humidity is the same over such a wide geographical area. (Nor is it legitimate to assume the radiated power of each station remains constant, but that's another matter.) If one disregards the pseudomathematical circular reasoning and looks only at raw signal voltages, the only legitimate inference is that humidity levels at the receiving site have an effect on the terminal voltage at the receiving antenna--which is exactly what one would expect of an electrically short vertical atop an unprotected insulator, feeding a high impedance voltmeter.
    In short, the data are meaningless.
For the experiment to prove the author's contentions, conditions over the signal paths would need to be known to at least some extent, the field strength would need to be measured with an environmentally protected active whip antenna or loop antenna, the transmitter parameters or transmit antenna current would need to be included, and the measured field intensities would need to be presented without any sort of doctoring. In the years since the article's first publication, this followup has not been forthcoming.
73,
John


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