MD,

The buried cable is niether Cat 3 or Cat 5, ask for PE 89. That is jelly filled for direct burial.

There are various numbers for the ariel, depending on what size, both strand and pair count.

You can buy Cat 5 for outside use but I've never seen it over four pair.

Any major supplier has both, Sprint of course has it for their local service companies so they have lots to offer. Graybar, Annixter, even some local electrical supply houses. Check around.
Rexell did have some of both available.

Make sure the supplier for the ariel has the correct hardware to hang it, ground it, and guy it.

Good Luck.

Ken
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