On Mar 13, 7:51*am, "William Sommerwerck"
wrote:
The signal is DC from a instrument, apyranometer. The output (0 to

5mV) is going to be scaled by 2000 to get 0 - 10V into a data
acquisition card. My concern is that having a signal in the low
millivolt range, and a cable of some 30-50' (exact length is not yet
known), noise would be a problem. This is a residential project, and
so there is no heavy machinery to speak of. Although I know this guy
has a shop and uses a lot of standard shop tools. So, my decision to
use coax is based on the fact that it's easy to make good field
connections and it "appear" to have better noise immunity than
shielded. There is a braided shield in coax; only a foil shield in
most shielded pairs.

"Common sense" suggests that you amplify the signal at the sending end, not
the receiving end.

"Common sense" also suggests that you use a balanced cable with a separate
shield. This is the way microphones are wired, and for very good reason.

As someone pointed out, a foil shield provides 100% coverage (or close to
it), while braided shields rarely do.

I'm not sure what your assumptions of my project are, but they have
led you to believe that I lack common sense. I have considered this
approach of amplifying at the sending end, and I may end up building a
voltage to current converter circuit to achieve this. This more
expensive approach would require a climate controlled nema 3r control
panel to be mounted on a roof, adding quite a few dollars to the
overall cost. I have 12 temperature sensors also mounted on the
system. I can not afford to build a sending circuit for each.