From: Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Date: Wed, 14 Jul 2010 18:06:05 +0200
Thread-Topic: RE: DLF passive received with earth antenna
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Subject: LF: RE: RE: DLF passive received with earth antenna
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Stefan, Jim, LF group,

I agree with Jim that an earth antenna most likely will not act completely=
 as a loop antenna.=20
But as an engineer it doesn't matter to me too much, I am more interested=
 in the efficiency of the antenna rather than how it works exactly.
To know the efficiency you would need to measure the power you can get out=
 af the antenna from the DLF signal.
Knowing the ERP of DLF, the path attenuation and the antenna RX power you=
 can calculate the antenna "gain".
To measure the antenna RX power properly you would have to cancel out any=
 reactive component of the antenna and terminate it properly.

73, Rik  ON7YD

________________________________________
Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.or=
g] namens James Moritz [james.moritz@btopenworld.com]
Verzonden: woensdag 14 juli 2010 15:49
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: LF: RE: DLF passive received with earth antenna

Dear Stefan, LF Group,

The EMF induced in a small loop is:

V =3D 2.1e-8 * fNAE

f =3D frequency
N =3D no. of turns
A =3D area
E =3D Electric field strength V/m (this assumes E/H =3D 377ohms, i.e. not=
 near
field)

This will be the voltage you measure, assuming negligible loading. As Rik
says, the ratio of voltages at a given frequency will be equal to the rati=
o
of loop areas - this holds provided the loops are a small fraction of a
wavelength in perimeter. With multi-turn loops, there may be errors caused
by distributed capacitance, etc., but probably not a significant problem=
 at
VLF.

Depending on the ground resistance and so on, this "earth antenna" might
also act as an E-field antenna, or combined E-field / H-field antenna, lik=
e
the K9AY and other "resistively terminated" loops. In this case, one would
expect a different signal voltage at each end of the loop.

Cheers, Jim Moritz
73 de M0BMU