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Re: LF: VLF propagation (continued..)

To: [email protected]
Subject: Re: LF: VLF propagation (continued..)
From: Piotr Młynarski <[email protected]>
Date: Thu, 06 May 2010 01:06:24 +0200
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Paul Nicholson wrote:

                                I'd like to see a plot of signal strength
against distance for 70km ionosphere and see how it compares
with the simple model in

Hello Paul, LF(VLF) Group,
sorry for the delay with my answer...
i have attached two figures. In the plot1.png file one can see calculated signal strength
against distance  with assumed D-layer height of 70 km.; f = 8.97 kHz
The decrease of signal strength does not have a strictly monotonic character - it 'oscillates' i.e. we have 'local' min and max values wrt the distance. For lower frequencies , say, up to 5-6 kHz the decrease is strictly monotonic - i've tested only a couple frequencies so i can not say precisely what is the frequency 'threshold' for such an 'oscillatory' behaviour for this particular
 earth-ionosphere waveguide propagation model.
In the second figure ( plot2.png file) i have simulated wide-band behaviour of that model so for the fixed distance of 858.7 km
(this was an arbitrary choice for fixing the distance)
and the same antenna parameters ( Stefan, dk7fc 2nd vlf tx'ing) there is a plot of signal strength versus frequency (please, note the logarithmic scales) One can see relatively big attenuation around 2 khz ( so called waveguide cutoff frequency ) and some 'resonances' when going into ELF region sorry for the 'coarse' sampling of frequencies taken for calculations but i simply wanted to check (quickly) both the wide-band properties of the earth-ionosphere waveguide as well as its present numerical implementation.

Yours, Piotr, sq7mpj
qth: Lodz /jo91rs/


PNG image

PNG image

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