Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

Absolutely I see what you describe below. Bournes actually has an old paper that describes all of these issues, but they do not seem to address them in selection guides these days. I have no way to find out which are good until I try 50 of them. I get a few that are just awful, basically a random

[time-nuts] TAPR "PulsePuppy" Pot Selection

Another very irritating "feature" of pots is that over time the wiper can deform the resistance element. When you go to adjust a pot (like when making a calibration adjustment on an old piece of equipment) it can be very difficult to get (and keep) the setting where you want it to be if the

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

Hi, Normally it's best to adjust a multi-turn trimmer in just one direction, so if you do overshoot, go back 2 or 3 turns and then on again to the place you want to be. The imperfections in the mechanism will drive you nuts (in a bad way) if you try to do fine adjustments back and forth. It's

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

In message , "Brian, WA1ZMS" writes: >I have seen similar issues to Dana's and have told myself it must >be torque left in the gear-train within the pot. Maybe all in my >mind as well, but it seems real to me on some equipment. Or simply

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

I have seen similar issues to Dana's and have told myself it must be torque left in the gear-train within the pot. Maybe all in my mind as well, but it seems real to me on some equipment. -Brian, WA1ZMS > On Dec 24, 2017, at 5:26 PM, Dana Whitlow wrote: > > I think I

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

I think I need to clarify what I mean by "backlash". It is not simple free play in the adjustment mechanism- it is something much more irritating, as follows: I sneak up on the desired result, but manage to overshoot slightly. So I back off on the screw, and find that at first the result

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

John wrote: 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. The hot tip is not to just "sneak[] up on the sweet spot and then walk[] away," as Dana put it.

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

I should comment that my bad experiences were in trimming out opamp DC offsets. As I recall, the amount of backlash was equivalent to a fair fraction of one turn of the shaft. I never fully trusted the philosophy of sneaking up on the sweet spot and then walking away- I felt it was necessary to

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

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

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

Hi With these little OCXO’s you likely will move them 0.1 ppb simply walking past the bench. If they have a total of 0.25 ppm of trim, a 25 turn pot will get you 1 ppb per turn. Setting these pots to 1/10 turn is not all that crazy. Yes, there are a bunch of assumptions made there and your

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

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 wrote: >John, > >Do you notice a

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

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

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

Hi The nice thing is that the footprint on the Pulse Puppy is pretty generic. There are a lot of OCXO’s on eBay that will fit the pattern on the board. When you get into the more exotic parts, the footprints (and functions) don’t tend to be as standardized. The small package OCXO’s will

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

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

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

Hi The other issue with putting in an amp is noise. You really do not want to feed a bunch of added “stuff” into the FM modulation port on the oscillator. You get some thermal noise from the pot, so it is never zero. How close you need to get to zero - who knows? When the part was tested to see

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

Mark is correct, but with a caveat: Unless the pot slider sees a load impedance that is much much larger than the pot's end-to-end resistance, contact resistance variations can also play a big role, especially when the pot gets old. For this reason alone I favor sticking with the 3-terminal

Re: [time-nuts] TAPR "PulsePuppy" Pot Selection

In message , Mark Goldberg writes: >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. I

[time-nuts] TAPR "PulsePuppy" Pot Selection

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.