Re: LF: AW: RE: Earth electrode loop area - I'm struggling

[Roger Lapthorn <rogerlapthorn@gmail.com>]

137kHz is a project for later this year Stefan.

73s
Roger G3XBM

2010/6/18 Stefan Schäfer <schaefer@hst.tu-darmstadt.de>

Interesting!
I wish i would know my ERP during the 9 kHz test where i reached 2km. But the grabber is still not calibrated :-(

Roger, when will you try 137 kHz?

73 es gl

Stefan/DK7FC

________________________________

Von: owner-rsgb_lf_group@blacksheep.org im Auftrag von Rik Strobbe
Gesendet: Fr 18.06.2010 23:10
An: rsgb_lf_group@blacksheep.org
Betreff: LF: RE: Earth electrode loop area - I'm struggling


Hello Roger,

my pennyworth:

assuming
- 50uW ERP
- antenna is traded as a loop (gain = -0.4dBd)

Due to the negative gain (-0.4dB versus dipole) a loop antenna must "radiate" 55uW to get 50uW ERP.
Since the antenna feeding current is 0.15A the radiation resistance is 2.44 milliOhm (R= P/I^2)
The radiation resistance of a small loop is : Ra = 320xPi^4*A^2/L^4
where A = loop area (m^2) and L = wavelength (m)
For 500kHz Ra = 5*10^(-7)*A^2 or A = 1416*sqrt(Ra)
If Ra = 0.00244 Ohm then effective the loop area is 70m^2

73, Rik  ON7YD - OR7T


________________________________

Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Roger Lapthorn [rogerlapthorn@gmail.com]
Verzonden: vrijdag 18 juni 2010 22:29
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: LF: Earth electrode loop area - I'm struggling


Please can someone help me with the maths? I've been trying to work out my effective loop area and I cannot get sensible answers. These are the measured or estimated numbers I have:

Voltage across "loop"  = 24.48V rms  - measured
Current flowing in "loop" = 0.15A - measured
ERP (from far field levels) = 50-100uW (may be less) based on -18dB S/N with M0BMU

>From these figures I should be able to work out the loop area, but either my calculations are wrong or the figure is correct and the effective loop area is very very small.

Help!

73s
Roger G3XBM

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