Hi Wim,

despite my wire is only 4mm in diameter, SWR does not vary at all applying a
steady full-power carrier (not even some small oscillations of the reflected
power meter needle). I then presume that no big corona effect takes place (also
because I see no corona light at dark). I am not sure whether a light corona
effect (i.e neither visible nor influencing SWR) could take place, but if so I
presume loss would anyway be very low.

I will check again under rain conditions (test not done so far), but I am not
sure whether rain increases susceptibility to corona, with respect to hot summer
days (with umidity close to 80% sometimes). Any idea at that regard?

73

Tony I0JX

Hello Tony,

It is not the voltage that will introduce loss (as the field lines will go
into air and frequency is low), but it is (corona) discharge. Whether this
occurs, depends on presence of sharp edges and especially sharp (double
curved) surfaces with small radius, think of bolts, threaded rods, etc that
point away from the tower into the air.

A thin end of an antenne element can also cause breakdown as it points far
into the air (away from other solid structures) and the voltage maximum will
be at the elements of your HF antenna.

In case of your 8 kVrms (that is 12 kVp), an antenna element with 10mm
diameter and spherical (smooth) end may result in 2.4kVp/mm at the end. If the
end of the element is just straight (just cut aluminium), you will exceed
3kVp/mm and corona will occur.

If (corona) discharge occurs, you will notice a sudden change in VSWR with
increasing power.


--
Wim
PA3DJS
www.tetech.nl
Please remove abc first in case of PM