[time-nuts] Re: James Miller/Brooks Shera 10 MHz GPSDO

[Mervyn Thomas]

Bob,

I'm with you on that and although I have 2 10811's I would be loathe to 
tear one apart - certainly as a last resort only and for information 
sake rather than being able to fix it.

Merv

On 2/09/2022 4:55 am, Bob kb8tq via time-nuts wrote:
> Hi
>
> The version you have simply has a “box” around a fairly normal
> 10811 OCXO. Tearing it apart is possible. It isn’t a whole lot of fun
> though.
>
> I still believe that the GPSDO board should put out +/- voltages
> and not just a negative voltage. Positive tune voltages are pretty
> common. Bipolar tune is unusual but not unheard of. Negative
> only tune is *very* rare.  Since the board is already out in the open,
> working on it should be easier than ripping open the OCXO.
>
> Bob
>
>> On Aug 31, 2022, at 11:21 PM, Mervyn Thomas via time-nuts <time-nuts at lists.febo.com> wrote:
>>
>> Hi Bob,
>>
>> I need to find a schematic to download for my particular version of the HP oscillator
>>
>> Merv
>>
>> On 31/08/2022 2:59 am, Bob kb8tq via time-nuts wrote:
>>> Hi
>>>
>>> If you check the 10811 schematic, the varicap is biased at roughly +6.8V internally.
>>> The other side of the diode is what the EFC is driving. This gives them the +/- 5V
>>> range they specify on the 10811 data sheet.
>>>
>>> Bob
>>>
>>>> On Aug 30, 2022, at 5:39 AM, paul swed via time-nuts <time-nuts at lists.febo.com> wrote:
>>>>
>>>> Pretty clever approach to establishing an offset. But doesn't it matter how
>>>> the vari-cap is hooked up in the oscillator circuit? If the veri-cap needs
>>>> a negative voltage to work that may indicate the cathode is at ground and
>>>> the positive voltage would forward bias the vari-cap. Just thinking about
>>>> the possible impact.
>>>> Though the cost of experimenting is $0. No harm.
>>>> Regards
>>>> Paul
>>>> WB8TSL
>>>>
>>>> On Tue, Aug 30, 2022 at 1:22 AM Mervyn Thomas via time-nuts <
>>>> time-nuts at lists.febo.com> wrote:
>>>>
>>>>> Stephen,
>>>>>
>>>>> An idea I may try -thanks for your response.  The current involved in
>>>>> the EFC line to the oscillator is extremely small-button cells would
>>>>> last years.
>>>>>
>>>>> Merv
>>>>>
>>>>> On 29/08/2022 8:42 pm, Stephen C. Menasian via time-nuts wrote:
>>>>>> Merv,
>>>>>>
>>>>>> If I understand your problem, the 10811's VCO control input voltage has
>>>>>> drifted above the output range of the GPSD driver board. If the VCO
>>>>>> control terminal current is low enough, you might be able to quickly
>>>>> solve
>>>>>> this problem by putting 1 or 2 Lithium Ion Coin cells in series with the
>>>>>> control lead. If only a few microamperes are involved, this solutin might
>>>>>> last several years.
>>>>>>
>>>>>> Stephen Menasian
>>>>>>
>>>>>> On Mon, 29 Aug 2022 15:56:52 +0800
>>>>>> Mervyn Thomas via time-nuts <time-nuts at lists.febo.com> wrote:
>>>>>>
>>>>>>> Hi Bill,
>>>>>>>
>>>>>>> Unfortunately the 2 HP 10811's I have have no way to poke anything thru
>>>>>>> the can to adjust a capacitor.  They are completely enclosed in an
>>>>>>> aluminium can with 2 power leads coming out with 6 pin female
>>>>>>> connectors on the end which go to the power board as used in the HP
>>>>>>> Z3801 GPSDO and 2 thin coax cables with SMB connectors - one marked as
>>>>>>> 10 MHz and the other as EFC.  I may have to replace mine with the model
>>>>>>> that has the tuning capacitor.
>>>>>>>
>>>>>>> Thanks for your response.
>>>>>>>
>>>>>>> 73   Merv
>>>>>>>
>>>>>>> On 29/08/2022 12:45 pm, Bill Beam via time-nuts wrote:
>>>>>>>> I also run a Brooks Shera/HP 10811. Still going after many years.
>>>>>>>> You must live with the limited steering voltage.
>>>>>>>> The solution is to adjust the HP 10811 tuning capacitor to get it
>>>>>>>> back near a frequency that the EFC can handle.
>>>>>>>> I have had to do this more than once.  Also if replacing the
>>>>>>>> oscillator its tuning capacitor may need adjustment.
>>>>>>>>
>>>>>>>> On Mon, 29 Aug 2022 11:25:26 +0800, Mervyn Thomas via time-nuts wrote:
>>>>>>>>
>>>>>>>>> Hi All,
>>>>>>>>> I'm new to time nuts but here goes.
>>>>>>>>> I built a GPS disciplined-  10MHz osc about 15 + years ago.-  It
>>>>>>>>> uses an HP 10811 D/Oven Oscillator and the Brooks Shera PCB and
>>>>>>>>> software V402N.- The physical construction article was per James
>>>>>>>>> Miller G3RUH. This unit has worked flawlessly for all these years
>>>>>>>>> but now is unable to hold the freq to precisely 10MHz - it is
>>>>>>>>> constantly .29 to.60 Hz high.- The DAC output which controls the EFC
>>>>>>>>> into the osc outputs a negative only adjustable voltage between -3v
>>>>>>>>> down to 0V and is settable by varying a 10K potentiometer.-  The
>>>>>>>>> Osc. now needs abouit +0.46V to bring it down to 10MHz but the DAC
>>>>>>>>> does not seem able to output a positive voltage.-  The DAC is an
>>>>>>>>> AD1861 (obsolete) and has a +5V applied to pin 16 and a -5V applied
>>>>>>>>> to pins 1 and 8. My first reaction was the HP osc. had reached the
>>>>>>>>> end of it's life but the datasheet states the EFC control voltage
>>>>>>>>> can be between a plus 5V and a minus 5V which varies the freq by 1Hz
>>>>>>>>> so it seems it is just over half way through it's life.
>>>>>>>>> I feel the Brooks s/ware would have provided some method to ensure
>>>>>>>>> the DAC output could be adjusted to swing the full full 5V or at
>>>>>>>>> least 3V?- I have the source code but I'm no programmer so would
>>>>>>>>> appreciate any help someone can provide please.
>>>>>>>>> 73 de Merv-  VK6BMT
>>>>>>>>> _______________________________________________
>>>>>>>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>>>>>>>> To unsubscribe send an email to time-nuts-leave at lists.febo.com
>>>>>>>> Bill Beam
>>>>>>>> NL7F
>>>>>>>>
>>>>>>>>
>>>>>>>>
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