Stefan, Jim, LF group,
I agree with Jim that an earth antenna most likely will not act completely as a
loop antenna.
But as an engineer it doesn't matter to me too much, I am more interested in
the efficiency of the antenna rather than how it works exactly.
To know the efficiency you would need to measure the power you can get out af
the antenna from the DLF signal.
Knowing the ERP of DLF, the path attenuation and the antenna RX power you can
calculate the antenna "gain".
To measure the antenna RX power properly you would have to cancel out any
reactive component of the antenna and terminate it properly.
73, Rik ON7YD
________________________________________
Van: [email protected] [[email protected]]
namens James Moritz [[email protected]]
Verzonden: woensdag 14 juli 2010 15:49
Aan: [email protected]
Onderwerp: LF: RE: DLF passive received with earth antenna
Dear Stefan, LF Group,
The EMF induced in a small loop is:
V = 2.1e-8 * fNAE
f = frequency
N = no. of turns
A = area
E = Electric field strength V/m (this assumes E/H = 377ohms, i.e. not near
field)
This will be the voltage you measure, assuming negligible loading. As Rik
says, the ratio of voltages at a given frequency will be equal to the ratio
of loop areas - this holds provided the loops are a small fraction of a
wavelength in perimeter. With multi-turn loops, there may be errors caused
by distributed capacitance, etc., but probably not a significant problem at
VLF.
Depending on the ground resistance and so on, this "earth antenna" might
also act as an E-field antenna, or combined E-field / H-field antenna, like
the K9AY and other "resistively terminated" loops. In this case, one would
expect a different signal voltage at each end of the loop.
Cheers, Jim Moritz
73 de M0BMU
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