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

 

 

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Van: [email protected] [[email protected]] namens Roger Lapthorn [[email protected]]
Verzonden: vrijdag 18 juni 2010 22:29
Aan: [email protected]
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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