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

[Mervyn Thomas]

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.
>>
>> 73Â Â  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-Â  10MHz osc about 15 + years ago.-Â  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.-Â  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.-Â  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-Â  VK6BMT
>>>> _______________________________________________
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>>> Bill Beam
>>> NL7F
>>>
>>>
>>>
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