I am the original poster of the question about the current-choke effect of
underground coax. I mentioned HF bands, with multiple coax runs (and control
cable runs) inside a 3" PVC conduit about 10" (top of PVC) underground. The
conduit is about 50' long. This is probably a very common situation.

Do I understand the sum of the comments correctly?
- A single buried coax (not inside a conduit) will experience a
significant current choke effect.
- Multiple coaxes (and other cables) inside a non-metalic conduit will
experience widely varying effects, depending on lots of parameters that
would be difficult to quantify in common usage.

One of my coax runs is for a half-sloper that is not very well matched at
any frequency. I detect no RF feedback into the shack (checking with the
little MFJ RF current meter, among other things). I had been wondering if I
should place current choke(s) on the coax on the tower, but I gather there
is probably no need for them.

Bill - W2WO