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

[paul swed]

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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