[time-nuts] HP Z3801 RB fun
Magnus Danielson
magnus at rubidium.se
Fri Dec 30 14:06:01 UTC 2016
I think the numbers given for 10811 sensitivity was grossly incorrect
from the source I had, so it should be +/- 1E-6 for +/- 5V, thus giving
2E-6 over 10V thus giving a sensitivity of 2E-7/V. Compare to 4E-10/V
fro the FRS-C and just redo the work.
I thought the numbers where funny but too tired to do extensive digging,
but I just wanted to show the general idea.
Cheers,
Magnus
On 12/30/2016 04:05 AM, paul swed wrote:
> Been interesting.
> Did increase the gain to 8 and remove the attenuation 10:1 needed for
> the piezo ocxo. Not sure I would say the system locks but it certainly
> slows the drift down to 10ns/30 minutes. I also added an offset after
> the amplifier. This allowed the Z3801 EFC to set its range more towards 50%.
> Though the FRS manual says the range is 0-5V for EFC the FRS is clearly
> offset with age to the +1.7V for center. (The other FRS was +.6V)
>
> Its interesting to see at the startup of the Z3801 the EFC range in the
> RB. Nice steps down towards a fairly low angle line according to Lady
> Heather.
>
> Have had to stop the experimentation late today to give a hand to a
> fellow on a HP 70-110GHz signal source. Till today I was a 10 GHz sort
> of guy.
> Regards
> Paul
> WB8TSL
>
>
>
> On Wed, Dec 28, 2016 at 6:51 PM, Magnus Danielson
> <magnus at rubidium.dyndns.org <mailto:magnus at rubidium.dyndns.org>> wrote:
>
> Hi,
>
> Well, that was the data I was able to find (and I referred to TvBs
> page where I found it). If you have more accurate data, please share
> so we can get the numbers right.
>
> The Z3801A will do a least square estimate of frequency error and then
> translate that into an initial DAC setting assuming it knows the EFC
> sensitivity, and the loop will work out the rest from there (hopefully).
> Getting EFC in the right neighborhood is probably wise for this reason.
>
> Cheers,
> Magnus
>
>
> On 12/29/2016 12:32 AM, Bob Camp 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
> <mailto: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
> <http://www.to-way.com/tf/frs.pdf>
>
> [2] http://www.leapsecond.com/pages/z3801a-efc/
> <http://www.leapsecond.com/pages/z3801a-efc/>
>
> [3] http://www.realhamradio.com/joe-geller.htm
> <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 <mailto: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
> <mailto: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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