[time-nuts] HP Z3801 RB fun

paul swed paulswedb at gmail.com
Wed Dec 28 18:48:36 EST 2016


​Magnus and Bob.
I appreciate the comments and the suggestions are easily implemented.
Technical term "Piece-O-cake".
One other note the the Z3801 uses a more negative voltage to raise
frequency while the Piezo and FRS use a positive voltage.
Absolutely agree on the offset​. Been trying to do that. However the FRS C
I am using wants seems to require +.6V to be on frequency. So because of
its age there may be a real issue. I have 3 others and may grab another to
see how it behaves. Also have some EGGs and FEI 5680s. Though those as I
recall are digital control.
But back to the basics first.
Regards
Paul.
WB8TSL

On Wed, Dec 28, 2016 at 6:32 PM, Bob Camp <kb8tq at n1k.org> wrote:

> Hi
>
> Ummm ….. errrrr ….
>
> The 10811 that is used in the Z3801 has a *larger* electrical tuning range
> than the standard
> 10811 not a smaller one. It’s tuning range and the TBolt OCXO’s tuning
> range are
> very similar.
>
> Bob
>
> > On Dec 28, 2016, at 6:22 PM, Magnus Danielson <
> magnus at rubidium.dyndns.org> wrote:
> >
> > Paul,
> >
> > We just want to help you with that curiosity, it sounds like a fun
> little project. :)
> >
> > The FRS-C [1] has a range of +/- 1E-9 over 0-5V, so EFC sensitivity is
> 4E-10/V.
> >
> > The Z3801A has a range of 5.20E-10 [2] over -5V to +5V [3], so EFC
> sensitivity is 5.2E-11/V.
> >
> > So, it looks like you need to have a gain of 8 and raise the EFC 2.5 V.
> >
> > Cheers,
> > Magnus
> >
> > [1] http://www.to-way.com/tf/frs.pdf
> >
> > [2] http://www.leapsecond.com/pages/z3801a-efc/
> >
> > [3] http://www.realhamradio.com/joe-geller.htm
> >
> > On 12/28/2016 11:42 PM, paul swed wrote:
> >> Magnus and Bob,
> >> Thank you for your response. As far as the original HO 10811 oscillator
> >> goes there is some well written details on it behavior and sensitivity.
> It
> >> was not the same as a standard 10811. A far smaller range as I recall.
> But
> >> the data is there.
> >> Its funny on the RB I have the EFC range from the spec sheet. It really
> >> tunes from 0-5V. But I find it interesting that the best alignment with
> >> other references is sub 1V. Its an old FRS C and I have others that may
> >> present a more centered range.
> >>
> >> I'll have to compare the detials that I have on the 10811 and FRS C.
> But I
> >> actually pulled out a 100:1 antenuator I was using on the Piezo crystal
> >> that indeed does lock.
> >>
> >> Goal in all of this is nothing special simply curiosity.
> >> Thanks again. When I have some real numbers to share I will.
> >> Regards
> >> Paul
> >> WB8TSL
> >>
> >> On Tue, Dec 27, 2016 at 10:26 PM, Bob Camp <kb8tq at n1k.org> wrote:
> >>
> >>> Hi
> >>>
> >>> The loop gain (as Magnus mentions) needs to be “correct” for the Rb.
> Since
> >>> the firmware was written for an OCXO with a PPM(ish) trim range,
> tacking it
> >>> on to a PPB(ish) Rb will require everything to scale by 1000:1. That’s
> 10
> >>> bits.
> >>> You may (or may not) have enough resolution in the math to handle that
> wide
> >>> a range of gains.
> >>>
> >>> If it really locks, the next challenge is to get it to run out to ~ 4
> days
> >>> or more on
> >>> the loop. Again, the firmware may or may not be able to do this.
> Unless it
> >>> does,
> >>> the Rb really will not lock as well as it could.
> >>>
> >>> With the Rb correctly locked, you still have the issue that the Rb is a
> >>> 2x10^-11
> >>> device (ADEV) at 1 second and the OCXO probably is 2x10^-12 (or
> better).
> >>> For
> >>> driving a counter with a normal gate, the Rb may not show much (if any)
> >>> improvement.
> >>> There is the slight chance the ADEV will get the firmware confused…..
> >>>
> >>> Since the firmware source is running around somewhere, you *could* dig
> into
> >>> all of this wonderful stuff :)
> >>>
> >>> Bob
> >>>
> >>>
> >>>> On Dec 27, 2016, at 8:33 PM, paul swed <paulswedb at gmail.com> wrote:
> >>>>
> >>>> OK so could not resist. The replacement of the HP 10811 with a PIEZO
> ocxo
> >>>> went very well. So in for a penny in for a pound. Why not an RB.
> Having a
> >>>> few around. Choice efratom FRS-c. Lot of thought went into this
> choice.
> >>> Not
> >>>> really it was there. It has a inverse frequency to EFC voltage just
> like
> >>>> the piezo and opposite the HP 10811.
> >>>> Well it connects runs and locks using the simple 1 opamp level ofset
> and
> >>>> and phase inverter.
> >>>> But locked is a funny comment. According to HPsatstat and LH. Its pll
> is
> >>>> locked. But both scope and the LH graph shows a very slow frequency
> drift
> >>>> that with the offset I can make positive or negative. A cycle at 10 ns
> >>>> takes quite some time about an hour compared to a TBolt and another
> non
> >>>> modified Z3801. At this level of resolution some things start to
> become
> >>>> questionable.
> >>>>
> >>>> I almost wonder if the modified z3801 under some level of drift
> assumes
> >>>> everything is locked and fine. Can it be pushed beyond expectations. I
> >>>> suspect it can.
> >>>> Anyhow as I say a bit of GPSDO fun.
> >>>> Regards
> >>>> Paul
> >>>> WB8TSL
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