[time-nuts] HP Z3801 RB fun

[Magnus Danielson]

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> 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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