"Bill Ogden" wrote in
:

I seem to remember reading that running coax underground acts like a
current choke. However, my memory has many missing bits these days.
Is this a true statement about coax underground? In my case the run
is about 40' (in a conduit that is about 10" under ground). I am
interested only in the normal HF bands.

A conductor carrying RF currents and immersed in soil behaves like a lossy
transmission line. The bahavior depends on the parameters of the soil
(amongst other things), so the effect is different in dry sand than in wet
clay. Current entering the line will be attenuated along the line.

Your coax is similar to some extent in respect to the common mode current.
Placing a single coax in a plastic conduit reduces the loss to some extent
compared to surrounding the cable directly with soil.

Owen