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Date: Thu, 24 Mar 2011 03:27:38 +0100
From: Piotr Mlynarski <sq7mpj@toya.net.pl>
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Subject: Re: VLF: Resonate the antenna, or not?
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Stefan Sch=C3=A4fer pisze:
> Wow, nice!
>
> Rik/ON7YD, now its your turn again: What will be the ERP when running=20
> 100A in that wire? I think 100A is realistic on such a wire. Skin=20
> depth should be 0.9 mm. So the effective conductor area 19 mm^2.=20
> Assuming 20m x 30m (?) wire (=3D600m^2) means 100m length, so R ~ 0.15=
=20
> Ohm. So Scott gets 100 A rms when running 1.5 kW into the antenna (no=20
> problem for the mains), without having problems of winding a large=20
> coil, without resonating, without ferrite parts, without high voltages=
=20
> (but high currents ;-) ). Am i right, Rik? And what is the ERP? I=20
> could take a look on your website but you can do it so well here! What=
=20
> is the L and Z and so the needed voltage to get 100A? :-)
> Instead of standard FETs, some IGBTs could be used, shouldn't be a=20
> problem at 9 kHz and some 100V. Any recommendations? :-)
>
> Scott, what FETs do you use in your design? The IRFP460 is OK for 20 A=
=20
> but not much more. One could do the effort and switch 4x 10 of them in=
=20
> parallel but you'll need a good driver, maybe IXDD430... Interesting=20
> stuff!
>
> 73, Stefan EI/DK7FC

Hi Stefan,  LF group

 Just before i was  going to switch off my computers and go to bed  =20
your mails arrived ....
 below my quick calculations   / Rik , pse, check it out :)  /
Al wire diameter 6.5 mm length 100 meters, f=3D 8970 Hz
skin depth: 0.925 mm   so Rac @ 8970 Hz  =3D 0.174 Ohm
20m x 30 m rectangular loop - its inductance L =3D 162.85 microHenry =20
/RA9MB equation/
radiation resistance Rrad =3D 0.008994 microOhm  / or using picoOhms as in=
=20
recent examples 8994 pOhm/
2*pi*f*L =3D 9.178 Ohm
2*pi*f*L/Rac =3D 52.72

using enough pwr to develop 100 Amp current  TX radiated is 89.94 microwat=
ts
loop over ground i.e. twice the Rad along with -0.39dBd loop gain=20
results in ERP =3D 164.4 microWatts
Voltage loop around 918 Volt

                                                           73, Piotr, sq7m=
pj

qth: Lodz /jo91rs/