[time-nuts] HP Z3801 RB fun
magnus at rubidium.dyndns.org
Wed Dec 28 18:22:43 EST 2016
We just want to help you with that curiosity, it sounds like a fun
little project. :)
The FRS-C  has a range of +/- 1E-9 over 0-5V, so EFC sensitivity is
The Z3801A has a range of 5.20E-10  over -5V to +5V , 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.
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.
> On Tue, Dec 27, 2016 at 10:26 PM, Bob Camp <kb8tq at n1k.org> wrote:
>> 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
>> 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
>> 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
>> device (ADEV) at 1 second and the OCXO probably is 2x10^-12 (or better).
>> driving a counter with a normal gate, the Rb may not show much (if any)
>> 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 :)
>>> 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.
>>> 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
>>> 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.
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/
>>> and follow the instructions there.
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/
>> and follow the instructions there.
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
More information about the time-nuts