Re: [time-nuts] GPSDO & Crystal Aging

[Magnus Danielson]

On 11/04/14 21:38, Chris Albertson wrote:

Look at what NTP does to select "good" clocks when it has many to choose
from.   It does not simply average them.

It looks at the noise in each one and then sees which clocks have
overlapping error bars.  It assumes that all good clocks have the same time
within limits of their precision.   Then from the good clocks there is a
second level weeding out process then finally it does a weighted average of
the remainders where I think those with less jitter get more weight.

It would not be impossible to do this with 10MHz oscillators.   Certainly a
simple average is not a good idea as a broken unit can pull the entire
average way down.  I think you'd have to check reasonableness first and
eliminate outliers   I think today you might simply digitize the signals
and figure out which were best using software.

In short the output is "ensemble time" (not "average time") but there is a
careful selection of who is allowed to be  member of the ensemble.


NTP uses the ensamble clock style that Dave Allan developed for the NBS 
AT time-scale and originally programmed on a PDP-7. Applying this type 
of phase-comparison, estimate stability, weighing and updating ensamble 
stability should indeed be possible to do. You need three or more 
clocks, but one of these can be the GPS when you have it.


Jim Gray pointed out that it is important to watch your data. At 
NBS/NIST they started to see some 1/f⁴ noise on one of their standards. 
They could not figure it out. Turned out that the cleaning-lady was 
pushing the standard over the floor once a week in order to clean under 
it. This systematic "noise" where not in their standard model, but they 
learned.


A frequency jump on the crystal oscillator in a control-loop will be 
tracked in eventually, so it will look more like a phase-spike than a 
frequency jump. Atomic clock FLLs will however not track in the full 
phase difference, at least not guaranteed to do.



I used a joke last week to explain to a class why we don't use averages,
with no other qualifications.  The joke is "Bill Gates walks into a bar
  What's the average net worth of everyone in the bar?  Maybe $250 million."

My point was that it is hard to describe a population that is not Gaussian
distributed.  "Stuck" and jumping crystals are not Gaussian.  You'd have to
detect the misbehaving devices.


Indeed.

Cheers,
Magnus
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Re: [time-nuts] GPSDO & Crystal Aging

[Magnus Danielson]

On 11/04/14 15:33, Tom Van Baak wrote:

Brooke, Ulrich,

Keep in mind the hp SmartClock product line dated from the early-90's and it was one of 
the first GPSDO on the market. So even simple things like using timing receivers, partial 
ionospheric correction, sawtooth correction, sub-ns TIC, 1PPS filtering, high-quality 
OCXO, PIID, DAC dithering, aging history and compensation would qualify as 
"smart". That's not to say there weren't other tricks going on.

One can learn a lot by playing with SCPI and pForth commands, as has been 
discussed here over the years. But the point is what was called smart 20 years 
ago may no longer be that magic. Page 6+ of the Kusters paper is interesting 
but nothing we don't already talk about weekly here.

Still, this is guessing. How about we find out for sure? Two ideas:

As a block box, a 58503A/Z3801A has only two inputs and two outputs. One input 
is the 1PPS from the Oncore VP (along with Motorola binary messages). The other 
input is the 10811. One output is 10 MHz, the other output is 1PPS, which is 
usually just locked to the phase of the LO. Or you could argue that there is 
really only one input (GPS 1PPS) and one output (DAC setting).

I propose someone on the list take a working 58503A and replace the Oncore VP 
with a pseudo GPS timing receiver and maybe also replace the 10811 with a DDS. 
In a very controlled manner, we can then mimic SA and post-SA jitter from the 
synthetic 1PPS. We can also mimic various oscillator phase and frequency 
behavior, including offsets, drift, and jumps using the DDS. The digital input 
to the DAC/EFC can be monitored to continuously track steering attempts. Or one 
could do man-in-the-middle games on the data to the DAC and avoid the need for 
the DDS.

By precisely watching how the SmartClock reacts to precise stimulus over 
seconds to days we can infer how the algorithms work with high confidence. Any 
number of people on the list can suggest clever stimulus scenarios to try. 
Unlike the GPSDO simulator (gpsim1), which can simulate a day in a seconds, the 
SmartClock experiment would have to run in real-time. That is, to infer how it 
handles aging prediction and holdover you'd actually have to let it run for a 
week.

The other idea, which I keep hoping Magnus will do, is to run the firmware 
under 68k emulation. It would be a large project, but I know he's already spent 
time on firmware disassembly.


I have spent a lot of time figuring a whole bunch of things out with the 
firmware. Lot's of it is boring like identifying libc routines, others 
is more interesting as figuring out the complete tree of SCPI commands 
as well as all the pFORTH commands. For each round I make I discover 
more, such as the minimum square loop that estimates the linear drift.


Tossing the code into a 68k emulation would be possible, but there is a 
bunch of things to simulate in it which relates to the hardware.


There is a general lack of decompiling tools, but I have been able to 
make more and more sense of what I got with the available tools. 
Unforunatly I have not been able to get the new version of the tool do 
anything useful without crashing on me.


Cheers,
Magnus
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Re: [time-nuts] GPSDO & Crystal Aging

[Chris Albertson]

Look at what NTP does to select "good" clocks when it has many to choose
from.   It does not simply average them.

It looks at the noise in each one and then sees which clocks have
overlapping error bars.  It assumes that all good clocks have the same time
within limits of their precision.   Then from the good clocks there is a
second level weeding out process then finally it does a weighted average of
the remainders where I think those with less jitter get more weight.

It would not be impossible to do this with 10MHz oscillators.   Certainly a
simple average is not a good idea as a broken unit can pull the entire
average way down.  I think you'd have to check reasonableness first and
eliminate outliers   I think today you might simply digitize the signals
and figure out which were best using software.

In short the output is "ensemble time" (not "average time") but there is a
careful selection of who is allowed to be  member of the ensemble.

I used a joke last week to explain to a class why we don't use averages,
with no other qualifications.  The joke is "Bill Gates walks into a bar
 What's the average net worth of everyone in the bar?  Maybe $250 million."

My point was that it is hard to describe a population that is not Gaussian
distributed.  "Stuck" and jumping crystals are not Gaussian.  You'd have to
detect the misbehaving devices.



David Allan had
> this interesting concept to the effect that if
> you had a sufficient number of wristwatches
> (maybe 1000) and you averaged them together
> you could somehow get a quality clock, or at
> least 31.6 times better.  Kind of like the
> notion of 1000 monkeys with 1000 typewriters...
>
-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] GPSDO & Crystal Aging

[WarrenS]

Ulrich

Thanks for posting the reference.
Very interesting and useful. The clues they give sounds like enough 
information to do the Smartclock loop control things that they talk about.


ws

***
Hi Brooke,


HP had some way around SA that improved the timekeeping.


HP called it the "Smartclock Algorithm" and you can find some very basic
information about it here:

http://www.hpl.hp.com/hpjournal/96dec/dec96a9.pdf

I have been trying months to find a reference on how it REALLY works but it
seems that this is one of the better kept secrets of HP.

Best regards

Ulrich 


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Re: [time-nuts] GPSDO & Crystal Aging

[bownes]

Interesting idea. It might be an interesting experiment to couple a large 
number of inexpensive xtals to see how it impacts effects such as sudden 
changes in a single xtal. 

With sufficient monitoring of each one, you could even tune the coupling to 
amplify/attenuate the results of the 'good' and 'bad' ones over some interval. 

Of course, what effect this has on things like phase noise, drift, and so on is 
a whole different matter. 

Bob

> On Apr 11, 2014, at 14:14, "Richard (Rick) Karlquist"  
> wrote:
> 
>> On 4/11/2014 11:04 AM, Hal Murray wrote:
>> 
>> How many would you need?  Is 3 enough?
>> 
>> How well could you do with several low(er) cost oscillators relative to one
>> good but expensive one?  It might be an interesting experiment in a nutty
>> sort of way.
> 
> My guess would be 3 would be a minimum, so you
> could have a majority vote.  Len Cutler's group
> actually built an experimental ensemble of 9 or
> 10, but it didn't seem to come to fruition.
> For this to make any sense, you would need to be
> able to cherry pick 9 or 10 really good oscillators.
> However, there was no way to get the production
> line to sign on to this.
> 
> David Allan had
> this interesting concept to the effect that if
> you had a sufficient number of wristwatches
> (maybe 1000) and you averaged them together
> you could somehow get a quality clock, or at
> least 31.6 times better.  Kind of like the
> notion of 1000 monkeys with 1000 typewriters...
> 
> Rick
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Re: [time-nuts] GPSDO & Crystal Aging

[Richard (Rick) Karlquist]

On 4/11/2014 11:04 AM, Hal Murray wrote:


How many would you need?  Is 3 enough?

How well could you do with several low(er) cost oscillators relative to one
good but expensive one?  It might be an interesting experiment in a nutty
sort of way.



My guess would be 3 would be a minimum, so you
could have a majority vote.  Len Cutler's group
actually built an experimental ensemble of 9 or
10, but it didn't seem to come to fruition.
For this to make any sense, you would need to be
able to cherry pick 9 or 10 really good oscillators.
However, there was no way to get the production
line to sign on to this.

David Allan had
this interesting concept to the effect that if
you had a sufficient number of wristwatches
(maybe 1000) and you averaged them together
you could somehow get a quality clock, or at
least 31.6 times better.  Kind of like the
notion of 1000 monkeys with 1000 typewriters...

Rick
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Re: [time-nuts] GPSDO & Crystal Aging

[Hal Murray]

rich...@karlquist.com said:
> Still, there was no way to guarantee that a crystal in the future would
> never have a jump or sudden change in aging.

> What was really needed was an ensemble of oscillators, but that was not
> economically competitive with rubidium.

How many would you need?  Is 3 enough?

How well could you do with several low(er) cost oscillators relative to one 
good but expensive one?  It might be an interesting experiment in a nutty 
sort of way.



-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] GPSDO & Crystal Aging

[Richard (Rick) Karlquist]

I worked for the HP Santa Clara Division during
the Smart Clock days and knew all the players.
In terms of holdover, the report cited mentions
temperature compensation and "learning" aging.
The temperature compensation was simply a crutch
for the 10811 to fix its tempco problems.  The
E1938A had much better tempco and eliminated the
need for this crutch.  As for the concept of
learning aging is concerned, there was definitely
no "secret sauce" I ever heard about in all the
Smart Clock powerpoints I sat through.  They
simply measured linear aging and possibly its
derivative and hoped that past performance would
predict future results.  It did to some extent,
but how well it worked depended on the particular
crystal.  A misbehaving crystal could not be
fixed by any cleverness in the algorithm.  Attempts
were made to screen crystals to get predictable
ones, and this was someone successful by getting
rid of bad actors.  Still, there was no way to
guarantee that a crystal in the future would never
have a jump or sudden change in aging.  What was
really needed was an ensemble of oscillators, but
that was not economically competitive with rubidium.

Rick

On 4/11/2014 3:06 AM, Ulrich Bangert wrote:

Hi Brooke,


HP had some way around SA that improved the timekeeping.


HP called it the "Smartclock Algorithm" and you can find some very basic
information about it here:

http://www.hpl.hp.com/hpjournal/96dec/dec96a9.pdf

I have been trying months to find a reference on how it REALLY works but it
seems that this is one of the better kept secrets of HP.

Best regards

Ulrich


-Ursprungliche Nachricht-
Von: time-nuts-boun...@febo.com
[mailto:time-nuts-boun...@febo.com] Im Auftrag von Brooke Clarke
Gesendet: Donnerstag, 10. April 2014 22:56
An: Tom Van Baak; Discussion of precise time and frequency measurement
Betreff: Re: [time-nuts] GPSDO & Crystal Aging


Hi Tom:

That makes sense because the GPS was just coming on line and
not anywhere near a full compliment of satellites and SA
was on.
HP had some way around SA that improved the timekeeping.
Has that ever been disclosed?

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

Tom Van Baak wrote:

Hi Brooke,

True, except that in most cases the long-term frequency

drift rate is

so tiny compared to all the short- and mid-term instability

that it is

not worth worrying about. In other words, I agree it is

modeled as a

"linear ramp", but the ramp, even at huge timescales, is so

close to

flat, what's the point?

Look at the output of a typical OCXO. Short-term the

frequency varies

by tens or hundreds of ps/s; that's parts in 10^11 or 10^10. By
contrast, you have wait an entire day or week before you get that
level of frequency error due to drift.

When you're in a rowboat outside SF bay, it's the 3 m waves

every 5 to

10 seconds that you need to steer against, not the 3 m tides that
occur gradually over 12 hours.

Can someone show me a counter-example? Why is it better to include
aging rate into the PID. What quantitative improvement in

performance

does this actually represent? I don't disbelieve it, I just

have never

seen the numbers.

One case where knowing the aging rate is important is during
multi-hour or multi-day holdover. Perhaps that's why HP

included the

128-hour circular record of frequency/aging into their firmware.

/tvb


Hi:

AFAICR the HP GPSDOs included the idea of measuring the

aging rate of

the crystal and applying that correction during holdover. This was
also mentioned by Brooks Shera in relation to his GSPDO

(there was a

plot), but I don't think it was part of the firmware?

So rather than just locking the control voltage to the last used
value it would be much better to add a linear ramp.
<http://www.rt66.com/%7Eshera/>



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Re: [time-nuts] GPSDO & Crystal Aging

[Tom Van Baak]

Brooke, Ulrich,

Keep in mind the hp SmartClock product line dated from the early-90's and it 
was one of the first GPSDO on the market. So even simple things like using 
timing receivers, partial ionospheric correction, sawtooth correction, sub-ns 
TIC, 1PPS filtering, high-quality OCXO, PIID, DAC dithering, aging history and 
compensation would qualify as "smart". That's not to say there weren't other 
tricks going on.

One can learn a lot by playing with SCPI and pForth commands, as has been 
discussed here over the years. But the point is what was called smart 20 years 
ago may no longer be that magic. Page 6+ of the Kusters paper is interesting 
but nothing we don't already talk about weekly here.

Still, this is guessing. How about we find out for sure? Two ideas:

As a block box, a 58503A/Z3801A has only two inputs and two outputs. One input 
is the 1PPS from the Oncore VP (along with Motorola binary messages). The other 
input is the 10811. One output is 10 MHz, the other output is 1PPS, which is 
usually just locked to the phase of the LO. Or you could argue that there is 
really only one input (GPS 1PPS) and one output (DAC setting).

I propose someone on the list take a working 58503A and replace the Oncore VP 
with a pseudo GPS timing receiver and maybe also replace the 10811 with a DDS. 
In a very controlled manner, we can then mimic SA and post-SA jitter from the 
synthetic 1PPS. We can also mimic various oscillator phase and frequency 
behavior, including offsets, drift, and jumps using the DDS. The digital input 
to the DAC/EFC can be monitored to continuously track steering attempts. Or one 
could do man-in-the-middle games on the data to the DAC and avoid the need for 
the DDS.

By precisely watching how the SmartClock reacts to precise stimulus over 
seconds to days we can infer how the algorithms work with high confidence. Any 
number of people on the list can suggest clever stimulus scenarios to try. 
Unlike the GPSDO simulator (gpsim1), which can simulate a day in a seconds, the 
SmartClock experiment would have to run in real-time. That is, to infer how it 
handles aging prediction and holdover you'd actually have to let it run for a 
week.

The other idea, which I keep hoping Magnus will do, is to run the firmware 
under 68k emulation. It would be a large project, but I know he's already spent 
time on firmware disassembly.

/tvb

- Original Message - 
From: "Ulrich Bangert" 
To: "'Discussion of precise time and frequency measurement'" 

Sent: Friday, April 11, 2014 3:06 AM
Subject: Re: [time-nuts] GPSDO & Crystal Aging


> Hi Brooke,
> 
>> HP had some way around SA that improved the timekeeping.
> 
> HP called it the "Smartclock Algorithm" and you can find some very basic
> information about it here:
> 
> http://www.hpl.hp.com/hpjournal/96dec/dec96a9.pdf
> 
> I have been trying months to find a reference on how it REALLY works but it
> seems that this is one of the better kept secrets of HP.
> 
> Best regards
> 
> Ulrich
> 
>> -Ursprungliche Nachricht-
>> Von: time-nuts-boun...@febo.com 
>> [mailto:time-nuts-boun...@febo.com] Im Auftrag von Brooke Clarke
>> Gesendet: Donnerstag, 10. April 2014 22:56
>> An: Tom Van Baak; Discussion of precise time and frequency measurement
>> Betreff: Re: [time-nuts] GPSDO & Crystal Aging
>> 
>> 
>> Hi Tom:
>> 
>> That makes sense because the GPS was just coming on line and 
>> not anywhere near a full compliment of satellites and SA 
>> was on.
>> HP had some way around SA that improved the timekeeping.
>> Has that ever been disclosed?
>> 
>> Have Fun,
>> 
>> Brooke Clarke
>> http://www.PRC68.com 
>> http://www.end2partygovernment.com/2012Issues.html
>> 
>> Tom Van Baak wrote:
>> > Hi Brooke,
>> >
>> > True, except that in most cases the long-term frequency 
>> drift rate is 
>> > so tiny compared to all the short- and mid-term instability 
>> that it is 
>> > not worth worrying about. In other words, I agree it is 
>> modeled as a 
>> > "linear ramp", but the ramp, even at huge timescales, is so 
>> close to 
>> > flat, what's the point?
>> >
>> > Look at the output of a typical OCXO. Short-term the 
>> frequency varies 
>> > by tens or hundreds of ps/s; that's parts in 10^11 or 10^10. By 
>> > contrast, you have wait an entire day or week before you get that 
>> > level of frequency error due to drift.
>> >
>> > When you're in a rowboat outside SF bay, it's the 3 m waves 
>> every 5 to 
>> > 10 seconds that you need to steer against, not the 3 m tides that 
>

Re: [time-nuts] GPSDO & Crystal Aging

[Ulrich Bangert]

Hi Brooke,

> HP had some way around SA that improved the timekeeping.

HP called it the "Smartclock Algorithm" and you can find some very basic
information about it here:

http://www.hpl.hp.com/hpjournal/96dec/dec96a9.pdf

I have been trying months to find a reference on how it REALLY works but it
seems that this is one of the better kept secrets of HP.

Best regards

Ulrich

> -Ursprungliche Nachricht-
> Von: time-nuts-boun...@febo.com 
> [mailto:time-nuts-boun...@febo.com] Im Auftrag von Brooke Clarke
> Gesendet: Donnerstag, 10. April 2014 22:56
> An: Tom Van Baak; Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] GPSDO & Crystal Aging
> 
> 
> Hi Tom:
> 
> That makes sense because the GPS was just coming on line and 
> not anywhere near a full compliment of satellites and SA 
> was on.
> HP had some way around SA that improved the timekeeping.
> Has that ever been disclosed?
> 
> Have Fun,
> 
> Brooke Clarke
> http://www.PRC68.com 
> http://www.end2partygovernment.com/2012Issues.html
> 
> Tom Van Baak wrote:
> > Hi Brooke,
> >
> > True, except that in most cases the long-term frequency 
> drift rate is 
> > so tiny compared to all the short- and mid-term instability 
> that it is 
> > not worth worrying about. In other words, I agree it is 
> modeled as a 
> > "linear ramp", but the ramp, even at huge timescales, is so 
> close to 
> > flat, what's the point?
> >
> > Look at the output of a typical OCXO. Short-term the 
> frequency varies 
> > by tens or hundreds of ps/s; that's parts in 10^11 or 10^10. By 
> > contrast, you have wait an entire day or week before you get that 
> > level of frequency error due to drift.
> >
> > When you're in a rowboat outside SF bay, it's the 3 m waves 
> every 5 to 
> > 10 seconds that you need to steer against, not the 3 m tides that 
> > occur gradually over 12 hours.
> >
> > Can someone show me a counter-example? Why is it better to include 
> > aging rate into the PID. What quantitative improvement in 
> performance 
> > does this actually represent? I don't disbelieve it, I just 
> have never 
> > seen the numbers.
> >
> > One case where knowing the aging rate is important is during 
> > multi-hour or multi-day holdover. Perhaps that's why HP 
> included the 
> > 128-hour circular record of frequency/aging into their firmware.
> >
> > /tvb
> >
> >> Hi:
> >>
> >> AFAICR the HP GPSDOs included the idea of measuring the 
> aging rate of 
> >> the crystal and applying that correction during holdover. This was 
> >> also mentioned by Brooks Shera in relation to his GSPDO 
> (there was a 
> >> plot), but I don't think it was part of the firmware?
> >>
> >> So rather than just locking the control voltage to the last used 
> >> value it would be much better to add a linear ramp. 
> >> <http://www.rt66.com/%7Eshera/>
> >
> >
> > ___
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> >
> 
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Re: [time-nuts] GPSDO & Crystal Aging

[Brooke Clarke]

Hi Tom:

That makes sense because the GPS was just coming on line and not anywhere near a full compliment of satellites and SA 
was on.

HP had some way around SA that improved the timekeeping.
Has that ever been disclosed?

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

Tom Van Baak wrote:

Hi Brooke,

True, except that in most cases the long-term frequency drift rate is so tiny compared to 
all the short- and mid-term instability that it is not worth worrying about. In other 
words, I agree it is modeled as a "linear ramp", but the ramp, even at huge 
timescales, is so close to flat, what's the point?

Look at the output of a typical OCXO. Short-term the frequency varies by tens 
or hundreds of ps/s; that's parts in 10^11 or 10^10. By contrast, you have wait 
an entire day or week before you get that level of frequency error due to drift.

When you're in a rowboat outside SF bay, it's the 3 m waves every 5 to 10 
seconds that you need to steer against, not the 3 m tides that occur gradually 
over 12 hours.

Can someone show me a counter-example? Why is it better to include aging rate 
into the PID. What quantitative improvement in performance does this actually 
represent? I don't disbelieve it, I just have never seen the numbers.

One case where knowing the aging rate is important is during multi-hour or 
multi-day holdover. Perhaps that's why HP included the 128-hour circular record 
of frequency/aging into their firmware.

/tvb


Hi:

AFAICR the HP GPSDOs included the idea of measuring the aging rate of the 
crystal and applying that correction during
holdover.
This was also mentioned by Brooks Shera in relation to his GSPDO (there was a 
plot), but I don't think it was part of
the firmware?

So rather than just locking the control voltage to the last used value it would 
be much better to add a linear ramp.




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Re: [time-nuts] GPSDO & Crystal Aging

[Poul-Henning Kamp]

In message , "Tom Van Baak" writes:

>True, except that in most cases the long-term frequency drift rate
>is so tiny compared to all the short- and mid-term instability that
>it is not worth worrying about.

... unless you care about holdovers of multiple days or weeks.

Otherwise:  I fully agree.

-- 
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Re: [time-nuts] GPSDO & Crystal Aging

[Tom Van Baak]

Hi Brooke,

True, except that in most cases the long-term frequency drift rate is so tiny 
compared to all the short- and mid-term instability that it is not worth 
worrying about. In other words, I agree it is modeled as a "linear ramp", but 
the ramp, even at huge timescales, is so close to flat, what's the point?

Look at the output of a typical OCXO. Short-term the frequency varies by tens 
or hundreds of ps/s; that's parts in 10^11 or 10^10. By contrast, you have wait 
an entire day or week before you get that level of frequency error due to drift.

When you're in a rowboat outside SF bay, it's the 3 m waves every 5 to 10 
seconds that you need to steer against, not the 3 m tides that occur gradually 
over 12 hours.

Can someone show me a counter-example? Why is it better to include aging rate 
into the PID. What quantitative improvement in performance does this actually 
represent? I don't disbelieve it, I just have never seen the numbers.

One case where knowing the aging rate is important is during multi-hour or 
multi-day holdover. Perhaps that's why HP included the 128-hour circular record 
of frequency/aging into their firmware.

/tvb

> Hi:
> 
> AFAICR the HP GPSDOs included the idea of measuring the aging rate of the 
> crystal and applying that correction during 
> holdover.
> This was also mentioned by Brooks Shera in relation to his GSPDO (there was a 
> plot), but I don't think it was part of 
> the firmware?
> 
> So rather than just locking the control voltage to the last used value it 
> would be much better to add a linear ramp.
> 



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[time-nuts] GPSDO & Crystal Aging

[Brooke Clarke]

Hi:

AFAICR the HP GPSDOs included the idea of measuring the aging rate of the crystal and applying that correction during 
holdover.
This was also mentioned by Brooks Shera in relation to his GSPDO (there was a plot), but I don't think it was part of 
the firmware?


So rather than just locking the control voltage to the last used value it would 
be much better to add a linear ramp.


--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

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