Hello,

Rik wrote:

It seems that even on 504 kHz still a lot of power is "absorbed" near the antenna.

If there are a few dBs still missing when all near field losses have
been taken into account, I would guess it is time to blame the
non-perfect ground. The lower the ground conductivity, the weaker
the low angle radiation radiation from the antenna. I don't think FS
measurements taken at ground level are reliable, there are too many
"it depends..." factors involved. Unfortunately, at 1km distance, the
FSM antenna has to be raised to almost 500m height to get a reading
at 25 degree elevation... Tethered balloon?

73
Johan SM6LKM