From: Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Date: Wed, 24 Feb 2010 17:01:54 +0100
Thread-Topic: AW: LF: VLF_8.79 kHz_grounding systems
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Subject: RE: AW: LF: VLF_8.79 kHz_grounding systems
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Hello Alexander,

if using a short vertical monopole antenna at 9kHz a ground loss of more=
 than 1000 Ohm seems quite realistic to me.
"Ground loss" at my QTH:=20
500kHz =3D 35 Ohm
137kHz =3D 130 Ohm=20
The frequency ratio is 3.65, the resistance ratio is 0.27 =3D 1/3.7
If this 1/f behaviour goes down to 9kHz (not sure) then at 9kHz the loss=
 resistance would be almost 2 kOhm.

Regarding the parallel capacitor: you are right, it will not reduce the lo=
sses. But it is much easier (and cheaper) to make a 3mH coil than a 30mH=
 coil and it will also transform the large loss resistance to a more conve=
nient value.

73, Rik  ON7YD - OR7T =20

________________________________________
Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.or=
g] namens Alexander S. Yurkov [fitec@omskcity.com]
Verzonden: woensdag 24 februari 2010 22:35
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: Re: AW: LF: VLF_8.79 kHz_grounding systems

>
> So, the coil losses decrease with it's L (assuming a given wire diameter=
,
> coil diameter and spacing and so on) and thus it is good to decrease the
> needed L.

You can decrease L only by condenser in parallel with a antenna.  But then
only part of coil current will flow thrue the ant (and ground stake also).
Let's describe some numerical example. Let antenna  capacity (denoted
as Ca) is 1 nF (large antenna!). Resistance of grounding we assume 1000
Ohm (huge resistance!). Parralel C (Cp) we assume to be 100 nF. Then L=3D3=
.2
mH. Let coil resistance is 1 Ohm (large coil!)  and coil current I is 1 A.
Then coil loss is 1 W. Antenna current for Ca<<Cp is (Ca/Cp)I =3D 0.01 A.
Grounding loss is (0.01)^2 * 1000 =3D0.1 W. With such a huge ground
resistance (unreally huge!) ground loss is only 10% of coil loss.

Regards,
Alexander