LF: Field Strength Measurements

[Chris Osborn <g3xiz@yahoo.co.uk>]

LF,

I've recently resurrected my old RF field strength meter as designed by PA0SE and published in the LF Experimenters' Handbook.

I've modifed it to measure signals in the MF band and have calibrated it with a home made Helmholtz coil arrangement.

This question may have been raised before but PA0SE gives the formula for deriving the transmitter power as

P = 0.0111 (Ed)^2  . . .   (1)

where E is the electrical field strength and d the distance

I've read in other places that the power from an isotropic radiator is

P = (Ed)^2 / 30

i.e.  0.0333 (Ed)^2  . . . . (2)

My calculated radiated power seems rather low so I'm wondering whether I should be using formula (2)

Any clarification would be most welcome.

73

Chris G3XIZ