I buried some 12v (but low current) coax for elements of a MW phased
shows two elements
with a step-on lawn edger when the lawn was wet, just below the
grass, the idea being just to keep it clear of the lawnmower and use the
dirt to attenuate common-mode RFI on its way to the antenna.
It also makes the coax easy to find (tune an AM radio to a weak station
and turn the radio so the station is just audible; when you drag the
radio across the coax, the signal level jumps up. Works every time.)
and repair (know the distances any connectors beforehand) since you
only have to scratch up a tiny bit of coax.
I don't know that conduit helps, in the sense that it will retain
water as well as shield from it. The dirt just below the grass is
usually dryish, which may be a better common state.
I've lost one of 8 cables to lightning in 8 years (so 64 cable-years)
but otherwise they work nicely. The lightning one wasn't a direct
hit but just a difference in ground voltage between the two ends of
a long run.
But you already have the trench, so the lawn edger suggestion has
little value, I guess.
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