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Date: 12 Jul 2001 11:06:34 +0100
Message-ID: <7D653C9C42F5D411A27C00508BF8803D55C54C@pdw-mail-r1.dstl.gov.uk>
From: "Andrew Talbot" <ACTALBOT@dstl.gov.uk>
To: rsgb_lf_group@blacksheep.org
Subject: RE: LF: LF/Hyper test
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 The far field of a radiated signal, where the reactive E and 
 H fields can be safely ignored in propagation loss 
 measurements, occurs at approximately lambda / 2.pi
 
 At this frequency, with a wavelength of 33.5km this occurs at 
 5.3km so you are still well within the near field.  Inside 
 this region the reactive E field falls off much faster than 
 1/R^2  and the magnetic field H even faster still, so the 
 decrease of 20dB going from R = 1.5 to 2.5km does not sound 
 too unreasonable.
 
 As a point to work from, "Reference Data for Radio Engineers" 
 gives groundwave loss at 10kHz for a 100km path as 33dB.  The 
 curve does not go much below 30dB loss so can't read off 
 smaller distances, but if you assume 1/R^2 as a first 
 approximation for the radiated field (although not strictly 
 true for groundwave propagation) it should give some very 
 rough indications of what to expect from the 5km range by 
 extrapolating back from 100km
 
The RSGB are still pursuing my 9kHz NOV application with the 
 authorities, eventually I hope to be joining in at these VLF 
 freqs one day !
 
 Andy  G4JNT
 
 
 > -----Original Message-----
 > From: Rik Strobbe [mailto:rik.strobbe@fys.kuleuven.ac.be]
 > Sent: 2001-07-12 10:42
 > To: rsgb_lf_group@blacksheep.org
 > Subject: Re: LF: LF/Hyper test
 > 
 > 
 > At 09:02 12/07/01 +0100, DJ2LF wrote:
 > >Some weeks before Markus DF6NM and me made some tests and 
 > found a max.
 > audible 
 > >distance of 1500m and a max. visible distance of 2500m (on 
 screen of
 > laptop). 
 > >Rec. antenna was 10m vertikal.
 > 
 > Hello Walter,
 > 
 > congrats on the 9kHz crossband QSO.
 > 
 > Did you measure the current you could get into the antenna ? 
 > Ground-loss
 > must be extreme at these frequencies.
 > 
> It is interesting to note that the signal seems to be audible 
 > up to 1.5km
 > and visible on screen up to 2.5km. If good software (argo, 
 spectogram
> etc..) was used this would mean that the signal level 
 > decreased about 20dB
 > between 1.5 and 2.5km !
> Or otherwise it would mean that you would have to increase 
 > power from 12W


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