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:
500kHz = 35 Ohm
137kHz = 130 Ohm
The frequency ratio is 3.65, the resistance ratio is 0.27 = 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 losses.
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 convenient value.
73, Rik ON7YD - OR7T
________________________________________
Van: [email protected] [[email protected]]
namens Alexander S. Yurkov [[email protected]]
Verzonden: woensdag 24 februari 2010 22:35
Aan: [email protected]
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=3.2
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 = 0.01 A.
Grounding loss is (0.01)^2 * 1000 =0.1 W. With such a huge ground
resistance (unreally huge!) ground loss is only 10% of coil loss.
Regards,
Alexander
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