Thanks, Roy,

and multiturn conductive plastic/cermet pots still have the same flat
element, say , 340 degree, but incude a vernier dial that changes turns
ratio?

Thks

"Roy Lewallen" wrote in message
...
Ivan Makarov wrote:
Hi, All,

can anybody tell if conductive plastic pots are non-inductive and can be
used for HF/50MHz ?
Same question re cermet pots.

The short answer is yes, but the long answer, as always, is more involved.

Nothing is truly non-inductive -- even a short straight piece of wire
has inductance. But the inductance of a conductive plastic or cermet pot
is only due to the physical length of the element. That is, it's as
small as it can possibly be for the physical size of the pot. That's in
contrast to a wire-wound pot which has many turns and a correspondingly
much higher inductance.

Whether you can use them at a given frequency depends on the particular
application. If you can tolerate a wire at that point in the circuit
which is the length of the pot's element (plus the distance to the
external connections), then you can tolerate the pot. Otherwise, you
might or might not be able to use the pot, depending on the relationship
between the inductance and resistance.

Because the element length is shorter, physically smaller pots have less
inductance than larger ones.

Roy Lewallen, W7EL

Ivan Makarov wrote:
Thanks, Roy,

and multiturn conductive plastic/cermet pots still have the same flat
element, say , 340 degree, but incude a vernier dial that changes turns
ratio?

I've seen pots of both types, but I think the only ones I've seen with a
multi-turn helical element were wirewound. I'd say look at the shape of
the pot -- if it's a flattened cylinder like a conventional pot, it's
probably got a single flat element. On ones I have like that, the
planetary vernier drive is obvious. But if it's shaped more like a tin
can, I'd suspect a multi-turn element.

Roy Lewallen, W7EL