"Andy"

I am working with an instrument which outputs 0-5mV, and that signal
has to reach a sensing device 35' away. I am concerned with noise,
and I don't think shielded cable will work well enough. So I am
considering using coax cable.

** Co-axial cable is a shielded cable.

But I don't understand coax. There are
numerous "RG" ratings and ohm ratings. Suppose I used RG62 with 50
ohm terminations. What do I need to know about the termination and
the cables in order to properly use this?

** Probably nothing - unless your mysterious "instrument" outputs signals
in the MHz range.

A run of co-axial cable with no special termination will present a
capacitive load to the source of about 22pF per foot - so in your example
about 770pF for RG59. Long as that capacitance is OK, along with whatever
load the input of the sensing device presents - you will be fine.

BTW

Co-axial cable has similar interference cancelling properties to twisted
pair cable.


...... Phil