[time-nuts] HP Z3801 RB fun

paul swed paulswedb at gmail.com
Thu Dec 29 22:05:10 EST 2016


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> 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>
>>> 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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