[time-nuts] TAPR "PulsePuppy" Pot Selection

Mark Goldberg marklgoldberg at gmail.com
Sun Dec 24 17:26:56 UTC 2017


I am using a Bournes 3224 and I do see backlash issues. I do come from one
direction to set it and if I overshoot, I go way past and come back from
the other direction. I also see non-monotonic sections. If one of those is
where you want to set the frequency, it is pretty hard to do. I chose one
with significantly lower impedance than the input impedance of the TCXO
control port. The 3296 datasheet has Adjustability specs and the 3224 does
not. The 3269 is only 12 turns but does have an Adjustability spec on the
datasheet. Maybe I will consider that. I would have to change my board to
use a throughole part.

Thanks for the info.

Mark


On Sun, Dec 24, 2017 at 8:58 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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