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

[Bob kb8tq]

Hi

If you spend some time shopping, 10811’s come up from time to time 
for around $50 or so ( delivered ) on eBay. At that price, buying four or 
five simply to have a few spares is probably a good idea. 

Bob 

> On Sep 2, 2022, at 12:45 AM, Mervyn Thomas via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> 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
>>>>>>>>>> _______________________________________________
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>>>>>>>>> Bill Beam
>>>>>>>>> NL7F
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
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