Hello Piotr, Stefan, Scott,
based on 6.5mm wire diameter and a skin depth of 0.925mm I come to an effective
area of 16.2mm and thus a resistance of 0.174 Ohm for 100m wire (based on a
resistivity for Al = 2.82E-8 Ohm*m, see
http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity#Resistivity_of_various_materials)
What is the same as Piotr's result.
Using IN3OTD's formula I come to a loop inductance of 161 uOhm what also agrees
well with Poitr's calculation.
The ERP values calulated by Poirt seem also correct to me.
The maximum current for a 6.5mm (2 AWG) Al wire is 100A DC (see
http://www.engineeringtoolbox.com/maximum-current-copper-aluminum-wire-d_1690.html).
At 9kHz the current runs only trough about 50% of the wire area (skin effect),
so 100A might be too much.
73, Rik ON7YD - OR7T
________________________________________
Van: [email protected] [[email protected]]
namens Piotr Mlynarski [[email protected]]
Verzonden: donderdag 24 maart 2011 3:27
Aan: [email protected]
Onderwerp: Re: VLF: Resonate the antenna, or not?
Stefan Schäfer pisze:
> Wow, nice!
>
> Rik/ON7YD, now its your turn again: What will be the ERP when running
> 100A in that wire? I think 100A is realistic on such a wire. Skin
> depth should be 0.9 mm. So the effective conductor area 19 mm^2.
> Assuming 20m x 30m (?) wire (=600m^2) means 100m length, so R ~ 0.15
> Ohm. So Scott gets 100 A rms when running 1.5 kW into the antenna (no
> problem for the mains), without having problems of winding a large
> coil, without resonating, without ferrite parts, without high voltages
> (but high currents ;-) ). Am i right, Rik? And what is the ERP? I
> could take a look on your website but you can do it so well here! What
> 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
> 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
> but not much more. One could do the effort and switch 4x 10 of them in
> parallel but you'll need a good driver, maybe IXDD430... Interesting
> stuff!
>
> 73, Stefan EI/DK7FC
Hi Stefan, LF group
Just before i was going to switch off my computers and go to bed
your mails arrived ....
below my quick calculations / Rik , pse, check it out :) /
Al wire diameter 6.5 mm length 100 meters, f= 8970 Hz
skin depth: 0.925 mm so Rac @ 8970 Hz = 0.174 Ohm
20m x 30 m rectangular loop - its inductance L = 162.85 microHenry
/RA9MB equation/
radiation resistance Rrad = 0.008994 microOhm / or using picoOhms as in
recent examples 8994 pOhm/
2*pi*f*L = 9.178 Ohm
2*pi*f*L/Rac = 52.72
using enough pwr to develop 100 Amp current TX radiated is 89.94 microwatts
loop over ground i.e. twice the Rad along with -0.39dBd loop gain
results in ERP = 164.4 microWatts
Voltage loop around 918 Volt
73, Piotr, sq7mpj
qth: Lodz /jo91rs/
|
