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

[Mervyn Thomas]

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
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>>>>>> Bill Beam
>>>>>> NL7F
>>>>>>
>>>>>>
>>>>>>
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