[TenTec] [SMC] OT: Half inch Andrews Heliax LDF4-50A vs LMR-400

[Stuart Rohre]

As to worrying about buried LMR 400, that would best be done before 
burying.  Any coax candidate for your use should state on its data 
sheet, or catalog page, "non contaminating jacket".  Even if it is that, 
I come from the old school, and to avoid unknown earth character as to 
acid or alkali content; I would bury a conduit of PVC, then insert the 
coax in that.  At the mid conduit, you want to put a spacer under it to 
raise the middle, before closing the trench, such that its center is 
slightly higher than either end, so that condensation will flow to the 
ends.  The ends should be weather resistant by putting on an elbow and a 
riser piece, and create by other elbows, a J type exit, with the "J" 
upside down.  The coax then exits facing the ground on each end.  If you 
don't glue the J parts, you can take off the elbows to swab out 
condensation that may collect at the bottom of the conduit.

The Wireman sells or did, some direct burial coax, and it is identified 
as such; but I still prefer to protect the coax.  Soil is dynamic, and 
rocks rise to the surface or move about, such that one might abrade and 
cut the jacket of direct buried coax.

For safety, be sure and ground the coax shield to a ground rod before 
the coax enters through your wall.  That is a good spot to install a 
coaxial surge arrestor as well, with short conductor without sharp 
turns, direct to the rod clamp  Rods should be driven nearly into the 
ground, leaving just enough for the clamp to be higher than rain water 
accumulates.

Stuart Rohre
K5KVH