[Lf] LF: Field strength MB2HFC and DC F139 at Windsor]

[Andre' Kesteloot]

Dick Rollema wrote:

> To All from PA0SE Whilst at the HF/LF Convention at
> Windsor I measured the field strength of the convention LF
> station MB2HFC, using my homemade portable instrument.
> Dave, G3MRF, provided the transport and Geri, DK8KW,
> accurately determined the distance to the transmitter from
> the two locations where the measurement was performed,
> using his GPS receiver. Both locations were in different
> directions from the transmitter and well outside the near
> field region (distance >2 wavelength). The field strength
> of MB2HFC measured at the two locations lead  to a
> radiated power of 485mW resp. 400mW. The average of about
> 450mW is considered to be the power actually radiated in
> the far field. The radiated power calculated as antenna
> current squared times the radiation resistance is probably
> considerably higher because power disappears in
> surrounding buildings and trees and also some power is
> radiated into the ground around the aerial (the latter in
> addition to the much higher power loss that is equal to
> the square of the current in the earth wire times the
> earth resistance!) Because a short monopole has a gain of
> 1.83 over a half wave dipole in free space and ERP is
> related to such a dipole MB2HFC's power of 450mW
> corresponds to an ERP of 823mW. I also measured the field
> strength of DCF139 at several locations at and around
> Windsor and found a consistent value of 0.78mV/m. At my
> home, 500km from Burg, where DCF139 is located, its FS is
> about 2mV/m, so 8dB higher. According to DK8KW and his GPS
> receiver the distance Burg - Windsor is 840km. Using the
> CCIR 150kHz curves for "Sea water" or "Land", which hardly
> differ, the difference in FS at 500 and 840km should be
> about 10dB, no too far from the 8dB measured.When using
> the "Land" curve for 150kHz the 2mV/m at my home yields a
> power radiated by DCF139 of 40kW which agrees reasonably
> well with the 50kW stated for this station. So the "Land
> curve" seems to be suitable for our purpose. 73, Dick,
> PA0SEJO22GD