James Miller/Brooks Shera 10 MHz GPSDO
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
Hi
The typical HP 10811 OCXO has a manual tuning adjust. You can re-tune
the unit over a pretty wide range by playing with a tuning tool. That should
allow you to hit whatever EFC target you need.
The AD1861
https://www.analog.com/media/en/technical-documentation/data-sheets/ad1851_1861.pdf https://www.analog.com/media/en/technical-documentation/data-sheets/ad1851_1861.pdf
Should put out +/- 3V according to the above data sheet. I don’t have
a schematic of the GPSDO here with me so there may be some other
“stuff” involved.
Bob
On Aug 28, 2022, at 7:25 PM, Mervyn Thomas via time-nuts time-nuts@lists.febo.com 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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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
Hi Mervyn,
I would suggest you use an extremely simple op-amp circuit to level shift
the DAC output by +3V or +4V as you see fit, instead of trying to modify
some 20-year old code which is otherwise perfectly functional.
Just my €0.02.
Cheers,
Andrew
On Mon, Aug 29, 2022 at 5:56 AM Mervyn Thomas via time-nuts <
time-nuts@lists.febo.com> 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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Hi Merv
I never built the Shera GPSDO but have studied it a bit. There were
numerous published versions of the source, with some mods possibly
better-researched than others. Not sure which one you have, or which PIC
chip you're using. Notes accompanying sourcefile PIC402NE_Final.asm say
it's for the PIC16C73, PIC16F73, PIC16F873A and PIC16F876A. From those
notes: "This is the final version of the GPS Discipline [sic] Controller
code released by Brooks Shera with a reformatting for readability and
corrected Auto_N and limiter routines. This is the final public release
code as of 4/10/13 with all fixes."
If you search that sourcefile for "ASCII input routines", you'll find a
summary of serial command formats which can be used for testing. In
particular you can override the DIP-switch settings and command the EFC
drive directly, which may at least let you see how far you can swing the
DAC and what effect that has on your oscillator. Also there's a command to
"replace [the] current PLL set point", which I haven't looked into but
which may allow some calibration.
Best of luck
Lloyd ZL2LEB
On Mon, 29 Aug 2022 at 15:54, Mervyn Thomas via time-nuts <
time-nuts@lists.febo.com> 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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Hi Merv,
I don't know about this GPSDO design, but the HP 10811 OCXO has a coarse
frequency adjustment capacitor on top of it.
You should be able to adjust this, so the EFC tuning voltage are again
inside the range of the potentiometer/DAC of the GPSDO.
Regards,
Askild
On Mon, Aug 29, 2022 at 5:56 AM Mervyn Thomas via time-nuts <
time-nuts@lists.febo.com> 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@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
I breadboarded the Shera GPSDO some 7 years ago. At that time some of
the ICs were no longer available, so I had to make some modifications.
As I recall, it wouldn't stay locked very long, perhaps because I didn't
adjust the resistor network between the DAC and the OCXO.
The AD1861 data sheet says its output voltage range is ~ +-3v. Its pin 8
is "NC", so that doesn't matter. Are you measuring the output voltage
right at the DAC output (pin 9 , 10), or at the VCXO itself? The
resistor network between these point changes the voltage range.
It's been quite a while, so I won't claim to be expert on the software
(in PIC assembly language), but I don't see anything there that would
preclude positive DAC outputs. I don't see a version number in the
source code, so I don't know if we have the same software.
I have these notes on the DIP switches:
DIP switches
("on" means low voltage, ie switch closed)
1-3 mode: 0 = setup, 1 = 30 sec time constant, 2-7 = successively
longer time constants
4 ocxo electronic tuning polarity: "on" if ocxo frequency decreases
with increasing EFC voltage
5 "on" allows changes to DAC (& EFC) voltage
Can you connect the RS-232 output from U10 ( a MAX233 ) pin 5 to a PC to
observe the ASCII output? If so, I could send you some info on
interpreting the three numbers that are sent.
I also have some more info on using the DIP switches that I could send
you, as well as a pdf of the original July 1998 QST article.
Also, you can put an analog voltmeter on PIC pin 2. The voltage range
is 0-2. The value will be about 1 if the measured phase difference is
near the controller's set point.
Dave WA8YWQ
On 2022-08-28 20:25, 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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Hi Askild,
Unfortunately the HP 10811's I have are in a completely enclosed can -
no holes to poke anything through. To get at any tuning capacitor would
probably entail taking the insides out of the can.
The oscillators like mine must have been fairly rare as I am unable to
find anything via Google. They have 2 main power leads coming out of
the can with 6 pin female connectors to connect to the power Power Board
which is out of an HP Z3801 GPSDO and 2 thin coaxes with SMB connectors
on the end - one marked as 10MHz and the other as EFC.
Regards, Merv
On 29/08/2022 1:09 pm, Askild via time-nuts wrote:
Hi Merv,
I don't know about this GPSDO design, but the HP 10811 OCXO has a coarse
frequency adjustment capacitor on top of it.
You should be able to adjust this, so the EFC tuning voltage are again
inside the range of the potentiometer/DAC of the GPSDO.
Regards,
Askild
On Mon, Aug 29, 2022 at 5:56 AM Mervyn Thomas via time-nuts <
time-nuts@lists.febo.com> 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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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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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@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@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.comBill Beam
NL7F
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