[time-nuts] HP Z3801 RB fun

[Bob Camp]

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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