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RE: LF: AW: 8.97kHz - Near field and radiated signals?

To: "[email protected]" <[email protected]>
Subject: RE: LF: AW: 8.97kHz - Near field and radiated signals?
From: Rik Strobbe <[email protected]>
Date: Wed, 26 May 2010 11:01:43 +0200
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Thread-topic: LF: AW: 8.97kHz - Near field and radiated signals?
Roger,
 
sorry, I made a mistake.
in the near field the H field drops 40dB/decade and the E-field drops 60dB/decade.
Assuming the ground antenna acts as a loop (= H-field) the signal drop between 0.4km and 3km will be 35dB.
The defintion of near field is vague, depending on the source it goes from 0.1 wavelength to 1 wavelength.
But at 1kHz even 0.1 lambda is 30km, so you are defenitely in the near field.
 
73, Rik  ON7YD - OR7T
 

Van: [email protected] [[email protected]] namens Roger Lapthorn [[email protected]]
Verzonden: woensdag 26 mei 2010 10:43
Aan: [email protected]
Onderwerp: Re: LF: AW: 8.97kHz - Near field and radiated signals?

Rick (et al),

I am confused by the near field attenuation rates quoted. Some quote 18dB for doubling distance which would mean an additional path loss of 56dB going from 0.4km to 3km. This makes a lot of difference to what may or may not be possible.

Which is the correct figure? Help!

73s
Roger G3XBM


On 26 May 2010 09:31, Rik Strobbe <[email protected]> wrote:

Roger,

 

the near fiels signal drops with the 3rd power of the distance.

So 3km versus 0.4km = 422 times weaker = -26dB

Going from regular CW to QRSS30 will give you a 24dB benefit, so there is a fair chance to be copied at 3km in this mode. Of course the signal needs to be very frequency stable, it has to be better than an free running oscillator.

Moving up in frequency would also help.

And if you can lay your hands on an old stereo amp it would provide an extra 10dB TX power.

 

Even if your goal is regular CW over a 3km path, starting with QRSS will most likely give a visible signal at 3km and allow you to watch any progress.

 

73, Rik  ON7YD - OR7T

 

 - The best DX targets are quite modest: I would like to exceed 1km


 initially with the TX power I currently have (around 4W). If I could reach
 G6ALB in the next village 3kms away I would be delighted. If I got any
 further I would be both amazed and VERY happy!



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