Re: LF: Re: 9kHz noise level

["James Moritz" <james.moritz@btopenworld.com>]

Dear Markus, LF Group,

I checked the noise level again during the daytime, and the noise level was 
about 6dB lower than last night, i.e. about 13uV/m per sqrtHz
One possibility for the discrepancy between results is that the effective 
height of your antenna is reduced at VLF compared to the LF calibration 
point. In my transmitting vertical field strength measuring sessions on 
500k, 136k and earlier 73k, the Heff of the same antenna works out 
consistently less as the frequency is reduced. I think this is due to 
increased "site loss" due to surrounding trees at the lower frequencies. 
H-field sensing loop antennas can be expected to be less affected. Of 
course, if there are no trees near your antenna, that theory is blown out of 
the water...
Cheers, Jim Moritz
73 de M0BMU