[time-nuts] TAPR "PulsePuppy" Pot Selection

John Ackermann N8UR jra at febo.com
Sun Dec 24 11:32:20 EST 2017


I didn't really notice much backlash, though when setting oscillators I try to approach (slowly) from one direction until it's "good enough" and then stop, to avoid that problem.

On Dec 24, 2017, 11:28 AM, at 11:28 AM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
>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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