EMRFD Message Archive 14558

Message Date From Subject
14558 2018-02-28 09:10:59 gamma_function Connecting variable capacitors

Hi all-

I'm building the LO stage of the 'Neophyte' receiver and am using a Hammarlund MC-140-S cap for tuning. And now I'm wondering... What is the best way to connect a cap like this to the rest of the circuit to minimize drift when building ugly-style, and also to preserve the possibility of using this component in future projects?


Brian KK6JTZ

14559 2018-02-28 12:29:12 Mike Re: Connecting variable capacitors

My 2 cents on your question about "what's the best way to connect a
variable capacitor for tuning of a Neophyte LO?": For the majority of
connections within a homebrew receiver, I would personally recommend
stranded wire (or coax, when shielding is important). But for wiring to
a tuning (LO) capacitor, I recommend solid conductor bus wire (or
insulated solid conductor wire). Keep the distance short from the
capacitor to the other tuned circuit components, and use a wire size
that's not likely to flex over the distance covered. Any flexing of the
conductor(s) will result in frequency shift. Using a solid conductor
rather than stranded will provide stiffness, and lessen drift or
frequency "wobble" that might otherwise occur from vibration.

Also, if possible, provide wire connections not only from the
capacitor's stator (insulated plates) to the other LO tuning components,
but also from the capacitor's frame (grounded plates) to the LO's
"local" ground circuitry.

I generally recommend stranded wire for all other connections because
it's less likely to develop a wire break (from repeated flexing or
vibration) that could interrupt a circuit.

Mike Dinolfo N4MWP

14560 2018-02-28 13:07:49 Tayloe, Dan (Noki... Re: Connecting variable capacitors
I have found that stiff wire tend to be more microphonic when used in VFOs, particularly for the "longer" runs to a variable capacitor.  I like to use #30 or #32 enamel wire because it is a bit limp and thus more vibrati
14561 2018-02-28 22:38:49 gamma_function Re: Connecting variable capacitors
Thank you. These are just the kind of details I was looking for.

Brian, KK6JTZ