[time-nuts] Re: Query about 5061B

[AC0XU (Jim)]

Tom- Thanks for the tips. Now that I understand about the LTC setting I am retesting my collection of 5061Bs in that mode. I was wondering about the 5071A, because as far as I can see, they don't have an "LTC" setting. Do they have any control settings that afftect the short-time ADEV? Also, you mentioned that you replaced the oscillator in one unit. How did that work out?
Jim




At 10:52 AM 11/9/2024, Tom Knox wrote:
>Hi Jim,
>The LTC mode is exactly what you are attempting to accomplish. I have not looked closely at the schematic, but as I remember changing the capacitor would only change the Loop Bandwidth when the control voltage is steering downward but would have little effect steering upward. If you plotted frequency instead of a sine wave you would see a slow downward slope with a steeper upward slope..
>
>If you have a really good 10811 I think changing the 12Meg resistor substantially higher will increase the LTC and utilize the superior close in Quartz performance. But looking at the variation 100K normal and 12 Meg LTC you will most likely need to increase a great deal perhaps start at 30Meg and go up. There could be a downside, with a resistor that high Randon noise may become an issue.
>All interesting, hopefully a fellow "Nut" has already been there, and will have actual results.
>This is exactly what I did in one of my 5071A, in which I replaced the 10811A with a ULPN 1000B.
>What may help you, I tend to look at short term/close performance with a focus on Phase Noise more than AD.
>Cheers,
>Tom Knox
>SR Test and Measurement Engineer
>Phoenix Research Group / Ascent Concepts and Technology / NIST
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>----------
>From: Jim Schatzman via time-nuts <time-nuts at lists.febo.com>
>Sent: Saturday, November 9, 2024 8:22 AM
>To: time-nuts at lists.febo.com <time-nuts at lists.febo.com>
>Cc: Jim Schatzman <james.schatzman at futurelabusa.com>
>Subject: [time-nuts] Query about 5061B 
> 
>Time Nuts-
>
>I think I posted an earlier version of this plot once before, which is ADEV for 7 different 5061B units. I accidentally tested unit #4 once with the cesium beam turned off and noticed a huge improvement in ADEV below tau = 500 secs. 
>I am wondering about the feasibility of improving the short time stability by increasing the time constant of the control circuit (A9 board). Looking at the schematic, there appears to be an 8 uf capacitor C2 which limits the bandwidth of the control amplifier. The input impedance in Oper is 100K, implying an RC time constant of 0.8 second. 
>
>I expect that adding some capacitance could make an improvement.  Has anyone tried this?   Any recommendations for the specific type of capacitor to use?
>
>While investigating, I note that the schematic shows a "LTC" position for S2. I didn't actually try that and I am going to do so.  I never realized what that meant!  The input circuit has R5 (Oper position) @ 100K and R6 (LTC) @ is 12M). A factor of 120!!
>
>Thanks-
>Jim
>
>
>Emacs!