As well as HB9ASB I have noticed that the match of the LF antenna had changed
considerably because of frozen ground, a change which could not be corrected
merely by retuning the resonance of the antenna.
Besides just noting the change It would have been interesting, of course, to
find out into what direction the ground resistance has changed. On one of the
last cold days and before the snow had disappeared I checked it with a resistive
bridge to find that the total feed point resistance of my antenna (when tuned to
resonance) had decreased from 100 ohms down to 60 ohms!!!
At present the main Variometer series loss is 18-20 ohms.
This would really be a nice gesture by nature: In the cold season not only the
QRN goes down, but also the ground resistance, leading to higher efficiency of
(amateur) LF antennas.
Now I will design a 250 uH variometer and a group of binary stepped capacitors
in the range 2 to 50 nF to be able to re-tune and re-match the antenna from the
73 Ha-Jo, DJ1ZB