[time-nuts] TAPR "PulsePuppy" Pot Selection

[Dana Whitlow]

John,

Do you notice a backlash effect when homing in on the desired setting with
those
tripots?  I last used such things back in the 1980's, and remember often
having
enough backlash to make close trimming rather difficult.

I wonder if they have gotten better in that regard.

Dana

On Sun, Dec 24, 2017 at 9:58 AM, John Ackermann N8UR <jra at febo.com> wrote:

> I'm glad that the PulsePuppy post spawned some good discussion!
>
> The pot I'm using is a Bournes 3296W-1-103LF which is a 25-turn, 10K,
> cermet pot, spec'd at 100ppm/degree, so it's not anything super fancy. The
> number of turns provides decent setability, and it seems to be a good match
> for the class of oscillator the PulsePuppy is designed for -- I found that
> I could trim the Isotemp oscillator without problems.
>
> I'll admit up front that the PulsePuppy wasn't designed as a host for
> ultra-stable oscillators.  I tried to keep the circuit board size and cost
> down, as well as the number of components that users would have to
> install.  And since the EFC trimmer is one of those user-installed parts,
> it's possible to substitute as nice a pot as you'd like.  I have one unit
> that's hooked up to an external precision pot with a turn-counter dial
> (just because it was there).
>
> John
> ----
>
> On 12/24/2017 03:57 AM, Mark Goldberg wrote:
>
>> Can you specify what pot you have used? I am using some for my TCXO boards
>> and am not quite happy with the settability or mechanical stability.
>> resulting in noise and higher Allan Deviation.
>>
>> A low noise regulator driving it also helped.
>>
>> I subscribe to the opinion to not use any extra resistors. When the pot is
>> used as a voltage divider, theoretically it should have the same TC
>> throughout, so temperature effects should not affect the divide ratio or
>> the output. Only the input impedance of the control voltage input to the
>> oscillator relative to the effective resistance of the pot will provide
>> some effect with temperature.
>>
>> Mark
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