[time-nuts] A better oscillator for the M12+T

[Stephan Sandenbergh]

Hi,

What will prevent me from de-soldering the oscillator on the M12+T and feed
it a stable, synthesized version (other words, same frequency as the current
oscillator) of my GPS steered OCXO? (This will be a heavily filtered, low
jitter signal of course) It seems to me I could improve timing performance
by quite a bit, without that much difficulty. I'm aware that the GPS
receiver includes some sort of temperature compensation inside the
controller, but what if I keep it at constant temperature?

I've heard of people trying this with other receivers. The theory says that
a better clock will improve the carrier to noise ratio, and thus also the
GPS measurements. Are there people around here that has tried it before?

Regards,

Stephan.
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[time-nuts] V standards

[Mark Sims]

I just snagged a 3457A for $250...  a 3458A would be nice,  but at $4K+ that 
extra digit is not worth it.   I once (briefly) owned a 3458A.  Got it for REAL 
cheap on Ebay (seller did not know what it was and mispellified everything in 
the listing title,  I was the only bidder that found it).  Powered it up,  yep 
it worked,  sold it the next day to a local cal lab for the proper value...  
gotta love illiterate/ignorant sellers.
_
Proud to be a PC? Show the world. Download the “I’m a PC” Messenger themepack 
now.
hthttp://clk.atdmt.com/MRT/go/119642558/direct/01/
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[time-nuts] My 5062C tale

[Tim Schulz]

Greetings, I thought I would update the list on the repair progress on 
my 5062C.  Some of you might recall that I had queried the list several 
months ago for troubleshooting help.  I would like to really thank Corby 
for the troubleshooting tips and Stan for the power supply page scans 
from the service manual.  It turns out that I had a dead ion pump high 
voltage power supply, but it took me a while to get the diagnosis.  I 
had thought it was the 18v power supply card.  This particular unit is a 
Navy 1695A/U badged model with the battery backup and all the optional 
features.  I got it off ebay about a year ago, and had been working 
pretty well for 8 months prior to the failure.  I had made an assumption 
that the 18V regulator card was bad because it looked seriously 
overheated, but the only way to know was to pull the bottom cover and 
probe the motherboard from below.  HP used these damn tinnerman nuts on 
the brackets to secure the sides of the cover and all of my screws were 
over torqued and the threads cut such that there was no way that the 
bottom was coming off without a fight.  In the mean time I won another 
5062C carcass of ebay missing its Cs tube but otherwise powering up and 
putting out signals.  I think that "I'll just swap 18V modules", but 
predictably that doesn't work and I have to drill out rivets holding the 
brackets and eventually figure out that the enabling signal from the ion 
pump power supply is not active.  The carcass has a ion pump power 
supply present, but it too is dead.  These are in little soldered shut, 
deep-drawn cans, so I carefully cut them open with a dremel moto tool 
and cut off wheels.  The innards look like a 17KHz switcher driving a 
pulse engineering transformer module and then a final (I assume) potted 
voltage multiplier.  I think the voltage multiplier is dead.  Anyway, I 
have a 2.5Kv 50ma power supply from an old IR scope tube and I wired 
that up though an old 100uA FS meter movement to the connector of the 
power supply module.  I also jumpered a resistor bridge onto the 18V PS 
enable signal line and reinstalled the module into the 5062C.  I had to 
put a variac on the input to the HV supply because it turned out to be 
too lightly loaded and the voltage was at 6Kv, arcing over to a near by 
cap.  There was an initial pretty high current reading, but it very 
quickly dropped to what looks like close to zero.  I powered the 
standard up and it and would give me a green light, and would stay green 
as long as I was in the shop, but the alarm light comes on and the green 
light goes out overnight.  All of the meter readings seemed to be normal 
for the 1st two days though the 2nd harmonic reading bounces between +25 
and +35 at about a 2hz rate.  Yesterday when I checked on it, the ion 
beam current had crept up past 50, so I turned it down to 30 and made a 
1st attempt to tweek the frequency adjustment.  Can't say that it made 
any difference, still got an alarm on the overnight run. I did find a 
smallish ionizer power supply that is flyback based and runs on 5v in 
the junk box that I was thinking about as a substitute.  The original 
standard says 2.6Kv on the PCB, and the newer model carcass says 3Kv - 
is the ion pump voltage critical?  Also, my Cs tube, PN 05062-60500, has 
an SN of 1516A0596.  I am assuming that its an old tube and that the 
only replacements will come from other machines... I looked at the FTS 
web site, didn't see any indication that they support it.  I was 
wondering what the remaining tube life might be and should I just keep 
the standard powered down most of the time with only the ion pump 
active.  Anyway, thanks again for the help!  tim

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Re: [time-nuts] VRefs - I'm a bigger Voltnut than a timenut..

[Neville Michie]

Hi,
Temperature is one quantity that is (or was) determined by physical  
properties of substances.
I have a platinum resistance thermometer, but alone it is useless.
The simplest way of using it is to connect it in 4 wire mode to a HP  
3468A multimeter,
and it measures the resistance with a resolution of about 1mK.
Connect it to another HP 3468A and it varies by less than 1mK.
So the HP 3468A measurement is robust.
Use a widely disseminated formula for the resistance of thermal pure  
platinum
and it seems to measure temperature.
Construct an ice-point cell with a dewar flask, shaved ice, a  
stirring rod and a syphon tube
and we seem to have calibration to better than 10mK.
I then built a hypsometer to boil water in.
The temperature of the steam did not shift 1mK in several hours.
But you have to use a barometer (Fortin pattern) to find the  
atmospheric pressure,
correct for the density of mercury,
correct for the expansion of the scale,
get an estimate for local gravity from
the Geoid, apply an altitude correction.
The result was that a $10 platinum resistance thermometer seems to be  
accurate to 1mK
but the ice-point calibration uncertainty may add plus or minus 5mK.

The big difficulty with temperature measurement is that you need  
circulating thermostat
baths to immerse things in to compare temperatures to any accuracy.  
You only need
one or two of those in your shack to have no room for your time  
standards, voltage standards etc.
cheers, Neville Michie










On 01/12/2008, at 12:24 PM, Predrag Dukic wrote:

>
> Obsession for precision is the same whether one is after Hertz,
> Volts, or Degrees of Celsius (Or Fahrenheit).
>
> The methods and technology are similar...
>
> I am now trying to fix two HP2804A quarz thermometers, thet are
> giving some error codes, and do not work.
>
> More or less they are oscillators, and measure of temperature is
> measured by frequency shift  between reference and external  
> oscillator.
>
> Reference frequency is unusual 10.000.000,8 in one of them (marked
> exactly so)  and 10.000.001  in the other.
>
> (Yes, yes, not a typo: it is 10MHz plus 0.8 Hz or plus 1.0 Hz)
>
> So precise temperature and precise frequency cross their ways...
>
>
> By the way, does anybody have op/serv manual for this thermometer?
>
>
> Predrag Dukic
>
>
>
>
>
>
> At 16:18 30.11.2008, you wrote:
>> Hello,
>>
>> there's currently no easy way to convert a frequency into Volt, i.e.
>> other than by cryo Josephson junction array or realizing Ohm by a
>> Klitzing quantum hall effect device. Otherwise, FLUKE would have
>> implemented that already in their Calibrators/Standards. They  
>> still rely
>> on Artefact Calibration, i.e. ovenized longterm stable Zener  
>> References
>> and Reference Resistors.
>>
>> The 5720A uses a stacked double Zener reference on a proprietary  
>> hybrid
>> circuitry, giving 1-2 ppm/year stability, the 7001 and 732B use the
>> LTZ1000 (Zener above BE junction), as the 3458A, the 732A uses the
>> Motorola device (Zener below BE junction), and the elder 332D and  
>> 335D
>> use similar, but less longterm stable references.
>> The LM199, AD587 and I think also the Geller device may only be  
>> used as
>> transfer standards, having poor longterm stabilities of 20ppm/yr.  
>> or more.
>>
>> Therefore, the LTZ1000 only may serve as a really affordable  
>> standard,
>> i.e. below 8ppm longterm stability, for private use.
>>
>> I was lucky to get some LTZ1000 samples, and used the standard  
>> circuit
>> from the LT datasheet for creating a small PCB. I purchased  
>> commercially
>> available wire wound resistors (TK 3, 25ppm/yr) for the 5 necessary
>> reference resistors and two OP07. Those resistors should give less  
>> than
>> TK 1 and 1ppm/yr additional drifts.
>>
>> Compared to my HP34401A, the circuitry showed quite good short term
>> stability below 1ppm, but shielding still has to be improved, as the
>> LTZ1000 circuit is susceptible to external EMC disturbances. This  
>> Volt
>> reference then costs less than 100 Euros/Dollars in total.
>>
>> I designed further circuitry (with TK 0.3 and TK 0.1 precision metal
>> foil resistors from Alpha and Vishay, chopper amp, precision switches
>> and Teflon insulated wires) to have the possibility for precision
>> transfers of the 7,2V reference voltage to 100mV, 1V, 10V, 100V,  
>> 1000V
>> level.
>> Only then, a Volt Standard is complete.
>>
>> All this stuff will emulate or replace the commonly needed 732A  
>> (ref),
>> 720A (Kelvin Varley), 752A (Reference Divider) and 834B (Null  
>> Detector).
>>
>> Got no time yet to finish and improve the system, and to do the  
>> repair
>> on an old 332B standard, but would like to share my knowledge, if
>> anyone's interested.
>>
>> Frank Stellmach
>>
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>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/ 
>> listinfo/time-nuts
>> and follow the instructions 

Re: [time-nuts] Voltage standards

[Lux, James P]

On 11/30/08 5:29 PM, "Brian Kirby" <[EMAIL PROTECTED]> wrote:

> A cryo may  be hard to put togather  (and maintain - from experience)
> but there are plenty of peltier junctions/devices out there...
>
> Brian KD4FM
>
> Lux, James P wrote:
>> Cost wise, I like the snippet I read in Scientific American a decade or so
>> ago.. LN2 is the cost of milk, LHe is the cost of fine scotch whisky
>> Is a obsessive precision worth a bottle of scotch?
>>
>> Jim

Can't get that cold with Peltiers.. Even 77K is a stretch. You run into a
problem with the maximum delta T from one device, and then having to suck up
the heat from that one.  You wind up with a pyramid shaped stack with
terrible efficiency.

The Melcor website has details.


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Re: [time-nuts] Voltage standards

[Bruce Griffiths]

WarrenS wrote:
> Bill Hawkins
>
> >From a theoretical standpoint, Zero Volts is the lower noise limit 
>
> If you want to reduce the measurement noise of a system you need to do one or 
> more of the following:
>
> Lower the source impedance, by reducing the resistance of the thing you are 
> measuring
> Lower the Bandwidth, by filtering over a longer time period
> Lower the temperature, by making it colder.
>
> Doing even any one of these things enough will in theory let the noise 
> approach zero, When you do two (or all three) at once the noise will approach 
> zero sooner.
> see "Johnson-Nyquist noise" for the details
>
> >From a practical standpoint, 1 nV of resolution is doable by comparing the 
> >difference between two voltage sources if one uses a lot of care and applies 
> >some form of extra filtering. 
> A  1nV  (1e-9) is way below the noise level of any voltage standard that puts 
> out volts.
> This means reference measurements are not limited by the noise level when 
> using a good but simple setup until the references gets to be in the 3e-10 
> precision range.
>
>   
Modern voltage references are somewhat noisier than standard cells and
batteries (at zero load current).
For the adventurous, recipes for constructing stable Weston standard
cells are readily available.
> The answer to "What can an amateur do to get a good low noise reference for 
> less than, say, $500"
> IS shop at the US eBay site.
>
> WarrenS
>
>   
Bruce

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Re: [time-nuts] Voltage standards

[WarrenS]

Bill Hawkins

>From a theoretical standpoint, Zero Volts is the lower noise limit 

If you want to reduce the measurement noise of a system you need to do one or 
more of the following:

Lower the source impedance, by reducing the resistance of the thing you are 
measuring
Lower the Bandwidth, by filtering over a longer time period
Lower the temperature, by making it colder.

Doing even any one of these things enough will in theory let the noise approach 
zero, When you do two (or all three) at once the noise will approach zero 
sooner.
see "Johnson-Nyquist noise" for the details

>From a practical standpoint, 1 nV of resolution is doable by comparing the 
>difference between two voltage sources if one uses a lot of care and applies 
>some form of extra filtering. 
A  1nV  (1e-9) is way below the noise level of any voltage standard that puts 
out volts.
This means reference measurements are not limited by the noise level when using 
a good but simple setup until the references gets to be in the 3e-10 precision 
range.


The answer to "What can an amateur do to get a good low noise reference for 
less than, say, $500"
IS shop at the US eBay site.

WarrenS

***
- Original Message - 
From: "Bill Hawkins" <[EMAIL PROTECTED]>
To: "'Discussion of precise time and frequency measurement'" 

Sent: Sunday, November 30, 2008 1:16 PM
Subject: Re: [time-nuts] Voltage standards


> Group,
> 
> The subject elicited a fine hardware discussion, as always.
> 
> There was some casual talk about measuring fractions of
> microvolts, implying 10E-7 or -8 accuracy.
> 
> There are lots of possible thermoelectric effects that may be
> in series with the source.
> 
> Without describing how it's done, what is the lower measuring
> limit in nanovolts? That's the limit where the last digit
> moves randomly by more than one increment. Does the method
> involve cryogenics?
> 
> I'd look it up, but I expect some of you are more current
> with the science than anything I could find with Google.
> 
> Given that extreme accuracy and stability are expensive, what
> can an amateur do for less than, say, $500 or 400 Euros?
> 
> Thanks for any enlightenment.
> Bill Hawkins
> 
> 
> 
> 
> 
>
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Re: [time-nuts] V refs -- Bruce

[Bruce Griffiths]

Richard Moore wrote:
> Bruce, The 714 opamp provides gain in the Datron 1082, and I would  
> use one LTZ1000 (or two in parallel, rather than try to use them in  
> series). A while back I tried using two LM399s in series in a Fluke  
> 895, and really didn't like the results -- a single 399 with an amp  
> was better in every way I could measure. As an alternative to a  
> chopper like the 1151, I might consider an OPA27. I have used the now  
> unobtainable OPA111 in the past, and that was a superb DC amp; they  
> (TI) claim the OPA27 is as good.
>
> Dick Moore
>   
Dick

Replacing the 120 ohm resistor with a PJFET  (source connected to Zener
- Q1 base junction, drain connected to ground) the gate of which is
driven by an opamp to regulate the collector base voltage of Q1 at zero
volts, whilst using the standard zener bootstrap circuit to provide the
zener current can reduce the effect of lead resistance variations by a
factor of 10 or more over the standard LTZ1000 circuit.

Bruce

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Re: [time-nuts] Voltage standards

[Brian Kirby]

A cryo may  be hard to put togather  (and maintain - from experience) 
but there are plenty of peltier junctions/devices out there...

Brian KD4FM

Lux, James P wrote:
> Exactly.. I'm sure I'm not the only one on this list that has contemplated 
> home use of liquid helium or even making the stuff.  Hey, if Onnes could do 
> it 100 years ago, so can we.
> 
> I assume the cryogen isn't being used for superconductivity in this case, but 
> for just being cold.  In which case, perhaps LH2 or LN2 would serve almost as 
> well.  The latter, particularly, is pretty manageable (i.e. You don't have to 
> make it yourself).
> 
> Cost wise, I like the snippet I read in Scientific American a decade or so 
> ago.. LN2 is the cost of milk, LHe is the cost of fine scotch whisky
> Is a obsessive precision worth a bottle of scotch?
> 
> Jim
> 
> On 11/30/08 2:13 PM, "M. Warner Losh" <[EMAIL PROTECTED]> wrote:
> 
> In message: <[EMAIL PROTECTED]>
> Bruce Griffiths <[EMAIL PROTECTED]> writes:
> : Cryogenic standards arent really feasible for home use as most require
> : liquid helium coolant.
> 
> This has got to be one of the best lines in a time-nuts email :)
> 
> Warner
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> 

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Re: [time-nuts] VRefs - I'm a bigger Voltnut than a timenut..

[Predrag Dukic]

Obsession for precision is the same whether one is after Hertz, 
Volts, or Degrees of Celsius (Or Fahrenheit).

The methods and technology are similar...

I am now trying to fix two HP2804A quarz thermometers, thet are 
giving some error codes, and do not work.

More or less they are oscillators, and measure of temperature is 
measured by frequency shift  between reference and external oscillator.

Reference frequency is unusual 10.000.000,8 in one of them (marked 
exactly so)  and 10.000.001  in the other.

(Yes, yes, not a typo: it is 10MHz plus 0.8 Hz or plus 1.0 Hz)

So precise temperature and precise frequency cross their ways...


By the way, does anybody have op/serv manual for this thermometer?


Predrag Dukic






At 16:18 30.11.2008, you wrote:
>Hello,
>
>there's currently no easy way to convert a frequency into Volt, i.e.
>other than by cryo Josephson junction array or realizing Ohm by a
>Klitzing quantum hall effect device. Otherwise, FLUKE would have
>implemented that already in their Calibrators/Standards. They still rely
>on Artefact Calibration, i.e. ovenized longterm stable Zener References
>and Reference Resistors.
>
>The 5720A uses a stacked double Zener reference on a proprietary hybrid
>circuitry, giving 1-2 ppm/year stability, the 7001 and 732B use the
>LTZ1000 (Zener above BE junction), as the 3458A, the 732A uses the
>Motorola device (Zener below BE junction), and the elder 332D and 335D
>use similar, but less longterm stable references.
>The LM199, AD587 and I think also the Geller device may only be used as
>transfer standards, having poor longterm stabilities of 20ppm/yr. or more.
>
>Therefore, the LTZ1000 only may serve as a really affordable standard,
>i.e. below 8ppm longterm stability, for private use.
>
>I was lucky to get some LTZ1000 samples, and used the standard circuit
>from the LT datasheet for creating a small PCB. I purchased commercially
>available wire wound resistors (TK 3, 25ppm/yr) for the 5 necessary
>reference resistors and two OP07. Those resistors should give less than
>TK 1 and 1ppm/yr additional drifts.
>
>Compared to my HP34401A, the circuitry showed quite good short term
>stability below 1ppm, but shielding still has to be improved, as the
>LTZ1000 circuit is susceptible to external EMC disturbances. This Volt
>reference then costs less than 100 Euros/Dollars in total.
>
>I designed further circuitry (with TK 0.3 and TK 0.1 precision metal
>foil resistors from Alpha and Vishay, chopper amp, precision switches
>and Teflon insulated wires) to have the possibility for precision
>transfers of the 7,2V reference voltage to 100mV, 1V, 10V, 100V, 1000V
>level.
>Only then, a Volt Standard is complete.
>
>All this stuff will emulate or replace the commonly needed 732A (ref),
>720A (Kelvin Varley), 752A (Reference Divider) and 834B (Null Detector).
>
>Got no time yet to finish and improve the system, and to do the repair
>on an old 332B standard, but would like to share my knowledge, if
>anyone's interested.
>
>Frank Stellmach
>
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Re: [time-nuts] Voltage standards

[David Forbes]

At 4:23 PM -0800 11/30/08, Lux, James P wrote:
>Exactly.. I'm sure I'm not the only one on this list that has 
>contemplated home use of liquid helium or even making the stuff. 
>Hey, if Onnes could do it 100 years ago, so can we.
>
>I assume the cryogen isn't being used for superconductivity in this 
>case, but for just being cold.  In which case, perhaps LH2 or LN2 
>would serve almost as well.  The latter, particularly, is pretty 
>manageable (i.e. You don't have to make it yourself).
>
>Cost wise, I like the snippet I read in Scientific American a decade 
>or so ago.. LN2 is the cost of milk, LHe is the cost of fine scotch 
>whisky
>Is a obsessive precision worth a bottle of scotch?
>
>Jim

I work in a lab where LHe is around much of the time. So it's not 
that far of a stretch for me to contemplate using it, although I 
don't personally handle the stuff.

We also have a few obsolete receiver Dewars lying around... one of 
them could be retrofitted to hold a cryogenic standard if we felt 
like it.

But there's the "rent" of regularly buying that LHe to keep the 
standard cold. Kinda like being a drunkard on fine Scotch whisky 
without the buzz.

-- 

--David Forbes, Tucson, AZ
http://www.cathodecorner.com/

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Re: [time-nuts] V refs -- Bruce

[Richard Moore]

On Nov 30, 2008, at 3:39 PM, tBruce wrote:

> Message: 6
> Date: Mon, 01 Dec 2008 11:53:32 +1300
> From: Bruce Griffiths <[EMAIL PROTECTED]>
> Subject: Re: [time-nuts] V refs
>
> The uA714 is claimed to be an OP07 equivalent.
> A chopper stabilised amplifier would have lower drift and flicker  
> noise,
> however the zener drift and flicker noise probably dominates.
>
> Stacking LTZ1000's in the same way is a little tricky.
> The only satisfactory method I have devised so far uses a PJFET as a
> voltage controlled resistor to sink the zener current whilst  
> allowing it
> to be reused to bias lower LTZ1000s in the series stack.
>
> Bruce

Bruce, The 714 opamp provides gain in the Datron 1082, and I would  
use one LTZ1000 (or two in parallel, rather than try to use them in  
series). A while back I tried using two LM399s in series in a Fluke  
895, and really didn't like the results -- a single 399 with an amp  
was better in every way I could measure. As an alternative to a  
chopper like the 1151, I might consider an OPA27. I have used the now  
unobtainable OPA111 in the past, and that was a superb DC amp; they  
(TI) claim the OPA27 is as good.

Dick Moore

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Re: [time-nuts] Voltage standards

[Lux, James P]

On 11/30/08 4:27 PM, "M. Warner Losh" <[EMAIL PROTECTED]> wrote:

> The thing that got me was the word 'really' in Bruce's statement.  It
> read like someone who had tried it, had limited success, but in the
> end wound up believing that while possible, it wasn't really
> practical.  After thinking that, I couldn't imagine that somebody on
> the list hadn't tried it for some reason or another over the years.
>
> After all, as you say, a fine bottle of scotch isn't that expensive
> when it comes to the pursuit of your obsessions :)
>
> Warner

And surely, with these grim economic times, liquid helium dewars are going
to be popping up on the surplus market. Then, at least, you'll have a place
to store that liquid helium.

And speaking of cryogens, has anyone on the list done cryogenic sapphire
ring oscillators? (at home)  After all, folks at JPL are doing this
" We present design progress and subsystem test results for a new short-term
frequency standard, the Voltage Controlled Sapphire Oscillator (VCSO).
Included are sapphire resonator and coupling design, cryocooler
environmental sensitivity tests, Q measurement results, and turnover
temperature results. A previous report presented history of the design
related to resonator frequency and frequency compensation [1]. Performance
goals are a frequency stability of 1×10-14 (1 second ≦ τ ≦100 seconds) and
two years or more continuous operation. Long-term operation and small size
are facilitated by use of a small Stirling cryo-cooler (160W wall power)
with an expected 5 year life." http://hdl.handle.net/2014/39769

Seems that running a cryocooler is probably a bit easier than pouring liters
of liquid helium into a cryostat.


Jim


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Re: [time-nuts] Voltage standards

[M. Warner Losh]

The thing that got me was the word 'really' in Bruce's statement.  It
read like someone who had tried it, had limited success, but in the
end wound up believing that while possible, it wasn't really
practical.  After thinking that, I couldn't imagine that somebody on
the list hadn't tried it for some reason or another over the years.

After all, as you say, a fine bottle of scotch isn't that expensive
when it comes to the pursuit of your obsessions :)

Warner


In message: <[EMAIL PROTECTED]>
"Lux, James P" <[EMAIL PROTECTED]> writes:
: Exactly.. I'm sure I'm not the only one on this list that has contemplated 
home use of liquid helium or even making the stuff.  Hey, if Onnes could do it 
100 years ago, so can we.
: 
: I assume the cryogen isn't being used for superconductivity in this case, but 
for just being cold.  In which case, perhaps LH2 or LN2 would serve almost as 
well.  The latter, particularly, is pretty manageable (i.e. You don't have to 
make it yourself).
: 
: Cost wise, I like the snippet I read in Scientific American a decade or so 
ago.. LN2 is the cost of milk, LHe is the cost of fine scotch whisky
: Is a obsessive precision worth a bottle of scotch?
: 
: Jim
: 
: On 11/30/08 2:13 PM, "M. Warner Losh" <[EMAIL PROTECTED]> wrote:
: 
: In message: <[EMAIL PROTECTED]>
: Bruce Griffiths <[EMAIL PROTECTED]> writes:
: : Cryogenic standards arent really feasible for home use as most require
: : liquid helium coolant.
: 
: This has got to be one of the best lines in a time-nuts email :)
: 
: Warner
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Re: [time-nuts] Voltage standards

[Lux, James P]

Exactly.. I'm sure I'm not the only one on this list that has contemplated home 
use of liquid helium or even making the stuff.  Hey, if Onnes could do it 100 
years ago, so can we.

I assume the cryogen isn't being used for superconductivity in this case, but 
for just being cold.  In which case, perhaps LH2 or LN2 would serve almost as 
well.  The latter, particularly, is pretty manageable (i.e. You don't have to 
make it yourself).

Cost wise, I like the snippet I read in Scientific American a decade or so 
ago.. LN2 is the cost of milk, LHe is the cost of fine scotch whisky
Is a obsessive precision worth a bottle of scotch?

Jim

On 11/30/08 2:13 PM, "M. Warner Losh" <[EMAIL PROTECTED]> wrote:

In message: <[EMAIL PROTECTED]>
Bruce Griffiths <[EMAIL PROTECTED]> writes:
: Cryogenic standards arent really feasible for home use as most require
: liquid helium coolant.

This has got to be one of the best lines in a time-nuts email :)

Warner
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Re: [time-nuts] bootstrap voltage standard to frequency standatrd

[Scott Burris]

As the original poster, I was hoping for something a hobbyist could 
build and run at (or close to) room temperature.  Without resorting to 
calibration.  Maybe in another decade.

Still, looking at the various tangents this question has spun off
is fascinating.  I always find myself learning new things listening
to the time-nuts list!

Scott

Clive Green wrote:
> Josephson Junction is the ultimate way to reference Voltage to Frequency.
> Mother nature having blessed us with time & frequency / ways of atomically
> referencing it so that this parameter may be generated & measured as a more
> accurate/lower offset/repeatable/stable way than any other parameter. Most
> other parameters can also be referenced to frequency.
> 
>  
> 
> Clive Green
> 
> CEO 
> 
> Quartzlock 
> 
> + Gothic, Plymouth Road, Totnes, Devon. TQ9 5LH England
> 
> (: +44 (0) 1803 862 062 7: +44 (0) 1803 867 962
> 
> š:   [EMAIL PROTECTED] ü:
>  www.quartzlock.com
> 
> Skype: clive.green.skype Messenger: [EMAIL PROTECTED]
> 
> Registered office: Gothic, Plymouth Road, Totnes, Devon. TQ9 5LH England
> Registered in England
> 
>  P Think Environment, print only if necessary.
> 
>  
> 
> This is an e-mail from Quartzlock (UK) Limited, its contents (including all
> attachments) and any files transmitted with it are confidential and intended
> solely for the individual(s) to which it is addressed and may also be
> privileged. It may not be copied or printed by anyone other than the
> addressee and may not be disclosed or distributed in any way.  If you have
> received this e-mail in error please inform Quartzlock (UK) Limited and
> delete it from your mailbox or any other storage devices.
> 
>  
> 
> Although this e-mail and any attachments are believed to be free of any
> virus or other defects which might affect any computer or IT system into
> which they are received, no responsibility is accepted by Quartzlock (UK)
> Limited or any of its directors, staff or associated businesses or contacts
> for any loss or damage arising in any way from the receipt or use thereof.
> 
>  
> 
> Opinions, conclusions and other information expressed in this message are
> not given or endorsed by Quartzlock (UK) Limited unless otherwise indicated
> by an authorised representative independent of this message.
> 
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Re: [time-nuts] Thoughts on Cs tube failure modes

[John Miles]

Hmm!  I appreciate the tip.  I'll confess it didn't occur to me to try to
force more current through the ion pump.  The supply I was using was limited
to about 300 uA, but I took your advice and tried a beefier one, set to 3
kV.  As I increased the current limit from 0 towards 5 mA, the ion-pump
current fell back to ~25 uA once I reached 1000 uA.

At the rate I was adjusting the current-limit control on the Glassman
supply, this occured about 10 seconds after power-up.  It seems stable now
at 25 uA, several minutes later.

I didn't leave the hot-wire ionizer energized for more than 10-15 seconds,
all told.  I'll let the ion pump run for a few hours, and then try the
hot-wire ionizer again.  Should I bother with the other supplies (Cs oven
heater, EM, mass spec), or is it reasonable to recondition the tube using
only the ion pump and hot-wire ionizer terminals?

Keep in mind that I don't have a 5062C mainframe, just the Cs tube and some
bench supplies.  I'm essentially recreating Tom's experiment from
http://www.leapsecond.com/pages/cspeak/ but without benefit of an actual
clock mainframe.  So I don't have a filament shutdown/recycle controller in
the picture.  Obviously that would be needed if I were to actually build a
clock around the tube, but for now, I just want to see if the tube is
functional at all, and determine its figure of merit.

-- john, KE5FX



> John,
>
> What you describe with the ion pump curent is normal if the tube has been
> powerd off for a long time.
>
> Th mainframe normally would turn the oven and ionizer filaments off when
> the ion pump current pegged.
>
> After minutes (can be quite a few minutes) the ion pump current will drop
> as it pumps the surge of outgassing from the heated filaments.
>
> The cycle repeats and can take a couple days on a stubborn tube.
>
> You bypassed that circuit so I'm not sure how much gas you introduced.
>
> If after a couple days the current is still pegged try connecting an
> external high voltage supply of around +3000VDC that can provide at least
> 5ma. (turn unit off)
>
> Let it run overnight and if the current comes down reconnect the internal
> power supply and turn the mainframe back on.
>
> You probably will see it peg again and the see the oven shut down (it
> happens fast!), just leave it on and it should start cycling and
> eventually the filaments will reach the oven set points and have
> outgassed enough so that the protective circuit will not trip.
>
> Then you can try to see if the rest of the tube has any life. (you may
> have to reduce the oven set resistor to 130 ohms as well as reducing its
> companion overtemp resistor. This is the value the Navy uses to get the
> last bit of life out of the tube, don't do it if you can get the rated
> beam current at the original value!)
>
> If you email me I can give you my evening phone number if you need some
> more info.
>


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Re: [time-nuts] V refs -- Frank S and Bill E

[Richard Moore]

Frank wrote:
>  The 5720A uses a stacked double Zener reference on a  
> proprietary hybrid
> circuitry, giving 1-2 ppm/year stability, the 7001 and 732B use the
> LTZ1000 (Zener above BE junction), as the 3458A, the 732A uses the
> Motorola device (Zener below BE junction), and the elder 332D and 335D
> use similar, but less longterm stable references.
> --

My Fluke 332D uses the Motorola IC (zener below) in a small Klixon  
oven which seems to be an on-off type with relatively poor temp  
control. Of course none of the divider string resistors or other  
circuits are in a temp-controlled space. I've found it very hard to  
keep that box under 10ppm over even short periods. It mostly sits.  
Did I mention its very big and heavy? It does supply 50mA at 1100V  
though.

Bill wrote:

> These use a rather clever way of generating 1V and 1.18 volts without
> significant division error. The 10V reference is sampled by a
> pulse-width modulator whose duty cycle is crystal-controlled and
> programmable. The result is then LP filtered using an active filter  
> and
> tracks the primary reference to better than 1ppm.
>
> Bill Ezell
> -

All of the newer Fluke calibrators use the PWM/LP filter method to  
vary output, as does my Valhalla 2701C DC 6-1/2 digit, 100mV-1000V  
reference. The Valhalla has an LM299 for its reference, and given its  
generally good overall performance, would be a good candidate for an  
LTZ1000 transplant. Another project.

Dick Moore

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Re: [time-nuts] V refs

[Bruce Griffiths]

Richard Moore wrote:
> On Nov 30, 2008, at 4:00 AM, Bruce wrote:
>
>   
>> Message: 1
>> Date: Sun, 30 Nov 2008 17:26:28 +1300
>> From: Bruce Griffiths <[EMAIL PROTECTED]>
>> Subject: Re: [time-nuts] V refs
>>
>> 
>
>   
>> 
>> Does the Datron use a series stack of zeners or does it use the once
>> popular ring of 2 reference circuit?
>>
>> Bruce
>> 
>
> Bruce, the 1082 uses two sets of two zeners in series. Each series  
> set of zeners has its own current setting resistor set. The out put  
> from each zener string is fed thru a 9.1k resistor into the + input  
> of an opamp mixer which drives an emitter follower, and that drives  
> the current setting resistors for the zeners, and, divided down, the  
> ref. output for the meter. The system actually works very well, but  
> given the ages of these meters, I suspect that the zero TC current  
> point of the zeners might need tweaking. The opamp is a Fairchild  
> uA714CH. I'm not familiar with its noise performance or, in this  
> system, its input temp characteristics -- I'll bet this also would be  
> a good spot for a chopper amp, if I switch to a LTZ1000
>
> Dick Moore
>
>   
Dick

The uA714 is claimed to be an OP07 equivalent.
A chopper stabilised amplifier would have lower drift and flicker noise,
however the zener drift and flicker noise probably dominates.

Stacking LTZ1000's in the same way is a little tricky.
The only satisfactory method I have devised so far uses a PJFET as a
voltage controlled resistor to sink the zener current whilst allowing it
to be reused to bias lower LTZ1000s in the series stack.

Bruce

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[time-nuts] bootstrap voltage standard to frequency standatrd

[Clive Green]

Josephson Junction is the ultimate way to reference Voltage to Frequency.
Mother nature having blessed us with time & frequency / ways of atomically
referencing it so that this parameter may be generated & measured as a more
accurate/lower offset/repeatable/stable way than any other parameter. Most
other parameters can also be referenced to frequency.

 

Clive Green

CEO 

Quartzlock 

+ Gothic, Plymouth Road, Totnes, Devon. TQ9 5LH England

(: +44 (0) 1803 862 062 7: +44 (0) 1803 867 962

š:   [EMAIL PROTECTED] ü:
 www.quartzlock.com

Skype: clive.green.skype Messenger: [EMAIL PROTECTED]

Registered office: Gothic, Plymouth Road, Totnes, Devon. TQ9 5LH England
Registered in England

 P Think Environment, print only if necessary.

 

This is an e-mail from Quartzlock (UK) Limited, its contents (including all
attachments) and any files transmitted with it are confidential and intended
solely for the individual(s) to which it is addressed and may also be
privileged. It may not be copied or printed by anyone other than the
addressee and may not be disclosed or distributed in any way.  If you have
received this e-mail in error please inform Quartzlock (UK) Limited and
delete it from your mailbox or any other storage devices.

 

Although this e-mail and any attachments are believed to be free of any
virus or other defects which might affect any computer or IT system into
which they are received, no responsibility is accepted by Quartzlock (UK)
Limited or any of its directors, staff or associated businesses or contacts
for any loss or damage arising in any way from the receipt or use thereof.

 

Opinions, conclusions and other information expressed in this message are
not given or endorsed by Quartzlock (UK) Limited unless otherwise indicated
by an authorised representative independent of this message.

 

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Re: [time-nuts] V refs

[Richard Moore]

On Nov 30, 2008, at 4:00 AM, Bruce wrote:

> Message: 1
> Date: Sun, 30 Nov 2008 17:26:28 +1300
> From: Bruce Griffiths <[EMAIL PROTECTED]>
> Subject: Re: [time-nuts] V refs
>

> 
> Does the Datron use a series stack of zeners or does it use the once
> popular ring of 2 reference circuit?
>
> Bruce

Bruce, the 1082 uses two sets of two zeners in series. Each series  
set of zeners has its own current setting resistor set. The out put  
from each zener string is fed thru a 9.1k resistor into the + input  
of an opamp mixer which drives an emitter follower, and that drives  
the current setting resistors for the zeners, and, divided down, the  
ref. output for the meter. The system actually works very well, but  
given the ages of these meters, I suspect that the zero TC current  
point of the zeners might need tweaking. The opamp is a Fairchild  
uA714CH. I'm not familiar with its noise performance or, in this  
system, its input temp characteristics -- I'll bet this also would be  
a good spot for a chopper amp, if I switch to a LTZ1000

Dick Moore

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Re: [time-nuts] Voltage standards

[M. Warner Losh]

In message: <[EMAIL PROTECTED]>
Bruce Griffiths <[EMAIL PROTECTED]> writes:
: Cryogenic standards arent really feasible for home use as most require
: liquid helium coolant.

This has got to be one of the best lines in a time-nuts email :)

Warner

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Re: [time-nuts] Voltage standards

[Bruce Griffiths]

Bill Hawkins wrote:
> Group,
>
> The subject elicited a fine hardware discussion, as always.
>
> There was some casual talk about measuring fractions of
> microvolts, implying 10E-7 or -8 accuracy.
>
> There are lots of possible thermoelectric effects that may be
> in series with the source.
>
> Without describing how it's done, what is the lower measuring
> limit in nanovolts? That's the limit where the last digit
> moves randomly by more than one increment. Does the method
> involve cryogenics?
>
> I'd look it up, but I expect some of you are more current
> with the science than anything I could find with Google.
>
> Given that extreme accuracy and stability are expensive, what
> can an amateur do for less than, say, $500 or 400 Euros?
>
> Thanks for any enlightenment.
> Bill Hawkins
>
>   
Bill

The lower limit depends on the detector or DVM used, together with ones
skill in eliminating thermoelectric effects.
With a sufficiently low noise front end detecting changes of 10nV or
less at room temperature is possible if the sources being compared are
sufficiently stable.
An ordinary DVM wont suffice (at least without a low noise preamp).

An LTZ1000 standard is feasible for for around $100, however whether you
get a really good one or one that just mets its specs depends on luck.

Building a null detector with say 10 nanovolt sensitivity is also possible.
Picovolt sensitivity usually requires cryogenic cooling.

With luck you may even be able to obtain an Fluke 720 KVD.
Failing that it is possible to build a 20 bit monotonic DAC with ppm
stability without requiring precision resistors.

Cryogenic standards arent really feasible for home use as most require
liquid helium coolant.

However graphene has supposedly exhibited the quantum Hall effect at
room temperature.

Bruce

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Re: [time-nuts] Trimble NTPX26AB

[Hal Murray]

> Newbie time-nut here. I recently acquired a Trimple GPS-disciplined
> Oscillator "C" (Seem to be a few on eBay) and have scoured the
> Internet for information. Nearest look-almost-alike seems to be the HP
> Z3801A but gather is doesn't speak Trimble protocol. 

If It has the same physical package as a Z3801A, I'd guess it was targeted at 
the cell phone tower market and probably speaks the same protocol, or a 
subset of the Z3801A commands.

Have you tried the Z3801A software?  I have a copy of something called 
satstat.

You can try it with your favorite terminal emulator.  19.2, 7bit, odd parity.

I think it will say something on power up.  You can check that with a scope.

If you feed it ":SYSTEM:STATUS?" and cr/lf, it might give you back a screen 
full of info.



-- 
These are my opinions, not necessarily my employer's.  I hate spam.




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Re: [time-nuts] Voltage standards

[Bill Hawkins]

Group,

The subject elicited a fine hardware discussion, as always.

There was some casual talk about measuring fractions of
microvolts, implying 10E-7 or -8 accuracy.

There are lots of possible thermoelectric effects that may be
in series with the source.

Without describing how it's done, what is the lower measuring
limit in nanovolts? That's the limit where the last digit
moves randomly by more than one increment. Does the method
involve cryogenics?

I'd look it up, but I expect some of you are more current
with the science than anything I could find with Google.

Given that extreme accuracy and stability are expensive, what
can an amateur do for less than, say, $500 or 400 Euros?

Thanks for any enlightenment.
Bill Hawkins




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[time-nuts] Trimble NTPX26AB

[Martin Richmond-Hardy]

Newbie time-nut here. I recently acquired a Trimple GPS-disciplined  
Oscillator "C" (Seem to be a few on eBay) and have scoured the  
Internet for information. Nearest look-almost-alike seems to be the HP  
Z3801A but gather is doesn't speak Trimble protocol.
Have noted http://www.febo.com/pipermail/time-nuts/2007-February/024213.html
I'm intending to use it mainly as a 10MHz source.
1. Does any one have/can point me to a pdf version of the Trimble  
manual? (I've tried the Trimble site)
2. Does the Thunderbolt software Tboltmon.exe work with this unit?
3. Any other advise?
Thanks

73 de
Martin Richmond-Hardy G8BHC
QTH: JO02pa
Skype: callto://martinrh45




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Re: [time-nuts] VRefs - I'm a bigger Voltnut than a timenut..

[wje]

Yes, I do have full schematics for the Datron refs, including the 
LTZ1000 circuitry. It isn't the same as that in the LTZ1000 data sheet. 
I'll dig out my manuals. If you'd like a copy, email your postal address 
and I'll copy the page and send it to you:

[EMAIL PROTECTED]

I've built a few standards myself. My latest was one using 16 399's. I 
shamelessly stole some circuit designs from a Fluke reference to provide 
sense-current compensation, etc. It was a lot of fun.

Bill Ezell
--
They said 'Windows or better'
so I used Linux.



Dr. Frank Stellmach wrote:
> @Bill Ezell:
>
> Well, I have the same motivation to invest time and money into "precision".
>
> I started with metrology working in a German Airforce cal lab  in 1980.
> We had all that goddie equipment, ie. a bank of Weston standard cells, 
> the Fluke cal system, DCF receiver, a HP caesium standard, and so on. 
> This cal lab was tightly associated with our PTB.
> In a "secret" lab they obviously made some tests on the new Josephson 
> junction standard, as they transferred the Volt from this lab to our 
> facility with a Fluke 731A, and they were very proud of that.
>
>  From then on, the ppm quest never let me go.
> It's biggest fun for me to design standards on my own, not only to 
> collect and repair old ones.
>
> I've already read about the Datron standards, but didn't know details, 
> and that it's so sophisticated. It's inner principle of dividing the 
> reference is identical to the Fluke 5720A, I think.
>
> Do you have a detailed schematic of the LTZ reference circuitry in the 
> Datron?
> This cannot be found in the manuals of HP3458 or Fluke 7000.
>
> In Germany there is no big chance for getting surplus standards for a 
> reasonable price.
> It's a pity..
>
> Frank
>
>
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>   

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Re: [time-nuts] Thoughts on Cs tube failure modes

[Corby Dawson]

John,

What you describe with the ion pump curent is normal if the tube has been
powerd off for a long time.

Th mainframe normally would turn the oven and ionizer filaments off when
the ion pump current pegged.

After minutes (can be quite a few minutes) the ion pump current will drop
as it pumps the surge of outgassing from the heated filaments.

The cycle repeats and can take a couple days on a stubborn tube.

You bypassed that circuit so I'm not sure how much gas you introduced.

If after a couple days the current is still pegged try connecting an
external high voltage supply of around +3000VDC that can provide at least
5ma. (turn unit off)

Let it run overnight and if the current comes down reconnect the internal
power supply and turn the mainframe back on.

You probably will see it peg again and the see the oven shut down (it
happens fast!), just leave it on and it should start cycling and
eventually the filaments will reach the oven set points and have
outgassed enough so that the protective circuit will not trip.

Then you can try to see if the rest of the tube has any life. (you may
have to reduce the oven set resistor to 130 ohms as well as reducing its
companion overtemp resistor. This is the value the Navy uses to get the
last bit of life out of the tube, don't do it if you can get the rated
beam current at the original value!)

If you email me I can give you my evening phone number if you need some
more info.

Corby Dawson
[EMAIL PROTECTED]




 

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Re: [time-nuts] VRefs - I'm a bigger Voltnut than a timenut..

[Dr. Frank Stellmach]

@Bill Ezell:

Well, I have the same motivation to invest time and money into "precision".

I started with metrology working in a German Airforce cal lab  in 1980.
We had all that goddie equipment, ie. a bank of Weston standard cells, 
the Fluke cal system, DCF receiver, a HP caesium standard, and so on. 
This cal lab was tightly associated with our PTB.
In a "secret" lab they obviously made some tests on the new Josephson 
junction standard, as they transferred the Volt from this lab to our 
facility with a Fluke 731A, and they were very proud of that.

 From then on, the ppm quest never let me go.
It's biggest fun for me to design standards on my own, not only to 
collect and repair old ones.

I've already read about the Datron standards, but didn't know details, 
and that it's so sophisticated. It's inner principle of dividing the 
reference is identical to the Fluke 5720A, I think.

Do you have a detailed schematic of the LTZ reference circuitry in the 
Datron?
This cannot be found in the manuals of HP3458 or Fluke 7000.

In Germany there is no big chance for getting surplus standards for a 
reasonable price.
It's a pity..

Frank


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Re: [time-nuts] VRefs - I'm a bigger Voltnut than a timenut..

[wje]

Another (sometimes) relatively inexpensive outstanding reference is 
either a Datron 4910 or 4912. These are also LTZ1000 based. The 10 has 
one reference, the 12 has four that can be averaged or used 
independently. You can on rare occasions pick one up for a few hundred. 
I have a pair, and yes, I paid Fluke $600 for traceable certification 
for one.

These use a rather clever way of generating 1V and 1.18 volts without 
significant division error. The 10V reference is sampled by a 
pulse-width modulator whose duty cycle is crystal-controlled and 
programmable. The result is then LP filtered using an active filter and 
tracks the primary reference to better than 1ppm.

My primary one was hot-shipped from Fluke after certification (it has 
battery backup) and hasn't ever been turned off. I have turned the 
secondary one on and off a few times, and the resultant error is less 
than 0.3 ppm. Both of these units had thousands of hours of burn-in 
before I got them, and I've added another 30 thousand or so.

I also have a Solartron 7081 8.5 digit meter, which is a marvelous unit. 
It uses a selected ultra-low TC Zener with a transistor for temp 
compensation, a sort-of discrete implementation of the LTZ1000. The 
Zener current is programmable, and is used to set the zero point for the 
particular zener/transistor pair. I can turn mine off for months at a 
time, turn it back on, and after a 24 h warmup, usually have it within 
1ppm(!) of my primary ref. These are somewhat rare, but can be picked up 
for a few hundreds. I paid $300 for mine.

As for why, I'm surprised that no one has stated the obvious reason - 
because you can. It's the same reason time-nuts collect 10e-13 frequency 
standards. I was into precision voltage and resistance metrology well 
before I got into precision frequency. I find it fascinating to be able 
to determine various values to precisions that not all that long ago 
were limited to national standards labs.

Bill Ezell
--
They said 'Windows or better'
so I used Linux.



Dr. Frank Stellmach wrote:
> Hello,
>
> there's currently no easy way to convert a frequency into Volt, i.e. 
> other than by cryo Josephson junction array or realizing Ohm by a 
> Klitzing quantum hall effect device. Otherwise, FLUKE would have 
> implemented that already in their Calibrators/Standards. They still rely 
> on Artefact Calibration, i.e. ovenized longterm stable Zener References 
> and Reference Resistors.
>
> The 5720A uses a stacked double Zener reference on a proprietary hybrid 
> circuitry, giving 1-2 ppm/year stability, the 7001 and 732B use the 
> LTZ1000 (Zener above BE junction), as the 3458A, the 732A uses the 
> Motorola device (Zener below BE junction), and the elder 332D and 335D 
> use similar, but less longterm stable references.
> The LM199, AD587 and I think also the Geller device may only be used as 
> transfer standards, having poor longterm stabilities of 20ppm/yr. or more.
>
> Therefore, the LTZ1000 only may serve as a really affordable standard, 
> i.e. below 8ppm longterm stability, for private use.
>
> I was lucky to get some LTZ1000 samples, and used the standard circuit 
> from the LT datasheet for creating a small PCB. I purchased commercially 
> available wire wound resistors (TK 3, 25ppm/yr) for the 5 necessary 
> reference resistors and two OP07. Those resistors should give less than 
> TK 1 and 1ppm/yr additional drifts.
>  
> Compared to my HP34401A, the circuitry showed quite good short term 
> stability below 1ppm, but shielding still has to be improved, as the 
> LTZ1000 circuit is susceptible to external EMC disturbances. This Volt 
> reference then costs less than 100 Euros/Dollars in total.
>
> I designed further circuitry (with TK 0.3 and TK 0.1 precision metal 
> foil resistors from Alpha and Vishay, chopper amp, precision switches 
> and Teflon insulated wires) to have the possibility for precision 
> transfers of the 7,2V reference voltage to 100mV, 1V, 10V, 100V, 1000V 
> level.
> Only then, a Volt Standard is complete.
>
> All this stuff will emulate or replace the commonly needed 732A (ref), 
> 720A (Kelvin Varley), 752A (Reference Divider) and 834B (Null Detector).
>
> Got no time yet to finish and improve the system, and to do the repair 
> on an old 332B standard, but would like to share my knowledge, if 
> anyone's interested.
>
> Frank Stellmach
>
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>
>
>   

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[time-nuts] VRefs - I'm a bigger Voltnut than a timenut..

[Dr. Frank Stellmach]

Hello,

there's currently no easy way to convert a frequency into Volt, i.e. 
other than by cryo Josephson junction array or realizing Ohm by a 
Klitzing quantum hall effect device. Otherwise, FLUKE would have 
implemented that already in their Calibrators/Standards. They still rely 
on Artefact Calibration, i.e. ovenized longterm stable Zener References 
and Reference Resistors.

The 5720A uses a stacked double Zener reference on a proprietary hybrid 
circuitry, giving 1-2 ppm/year stability, the 7001 and 732B use the 
LTZ1000 (Zener above BE junction), as the 3458A, the 732A uses the 
Motorola device (Zener below BE junction), and the elder 332D and 335D 
use similar, but less longterm stable references.
The LM199, AD587 and I think also the Geller device may only be used as 
transfer standards, having poor longterm stabilities of 20ppm/yr. or more.

Therefore, the LTZ1000 only may serve as a really affordable standard, 
i.e. below 8ppm longterm stability, for private use.

I was lucky to get some LTZ1000 samples, and used the standard circuit 
from the LT datasheet for creating a small PCB. I purchased commercially 
available wire wound resistors (TK 3, 25ppm/yr) for the 5 necessary 
reference resistors and two OP07. Those resistors should give less than 
TK 1 and 1ppm/yr additional drifts.
 
Compared to my HP34401A, the circuitry showed quite good short term 
stability below 1ppm, but shielding still has to be improved, as the 
LTZ1000 circuit is susceptible to external EMC disturbances. This Volt 
reference then costs less than 100 Euros/Dollars in total.

I designed further circuitry (with TK 0.3 and TK 0.1 precision metal 
foil resistors from Alpha and Vishay, chopper amp, precision switches 
and Teflon insulated wires) to have the possibility for precision 
transfers of the 7,2V reference voltage to 100mV, 1V, 10V, 100V, 1000V 
level.
Only then, a Volt Standard is complete.

All this stuff will emulate or replace the commonly needed 732A (ref), 
720A (Kelvin Varley), 752A (Reference Divider) and 834B (Null Detector).

Got no time yet to finish and improve the system, and to do the repair 
on an old 332B standard, but would like to share my knowledge, if 
anyone's interested.

Frank Stellmach

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[time-nuts] Blatent plug Sidereal frequency standard

[Robert Atkinson]

Hi all, Pardon the blatent plug, I just put an HCD research OCXO sidereal 
(5.0136895 MHz xtal) frequency reference on ebay. See item 260323643052.
Robert G8RPI.


  
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Re: [time-nuts] Thoughts on Cs tube failure modes

[Bruce Griffiths]

John Miles wrote:
> I recently found a tube from a 5062C on eBay in unknown condition for not
> *too* much money, and thought it would be interesting to power it up on the
> bench.  Once I got it and saw the 19xx-prefix serial number, I wasn't too
> optimistic, since it could potentially be 25 years old or more.  Things went
> well for the first few steps of the process, but then the experiment failed
> big-time.
>
> 1) I first applied +2600V to the ion pump with nothing else connected.  Spec
> is < 10 uA.  There was a brief spike to ~100 uA, but within a few seconds,
> the current began to drop rapidly, ending up at about 1 uA after a few
> minutes.  So far, so good.
>
> 2) I then brought the Cs oven up to temperature slowly with a variable
> supply.  The 5062C runs its oven in a thermostatic loop, but it was easy
> enough to warm the oven up slowly over 10 minutes or so, watching the
> thermistor resistance to achieve the 200-ohm reading indicated on the tube
> label.  The ion pump current rose to about 2.5 uA during the Cs oven warmup
> process.
>
> 3) I then attempted to bring up the hot-wire ionizer, which takes 1 volt at
> about 1.6 amps (when hot).  Simultaneously, the 22-mA C-field current and
> 13.9-volt mass-spec supply was applied.  As with the Cs oven, I brought the
> ionizer voltage up slowly.
>
> 4) At that point the ion pump supply went into full current limiting at
> circa 300 uA.
>
> I killed the power quickly, removed the oven and hot-wire ionizer supplies,
> and tried powering the ion pump up by itself once again.  Although a DMM
> check indicated infinite resistance across the ion pump, the HV supply still
> went into current limiting.
>
> I'm guessing that the hot-wire ionizer element had enough crud on it to kill
> the vacuum when it vaporized.  The tube envelope is probably OK, because the
> ionizer wire itself didn't burn out.  Unfortunately I was watching only the
> hot-wire ionizer current during that part of the process, so I don't know if
> there was a point where I could have observed a rise in ion pump current and
> backed off in time to avoid permanent damage.
>
> The last step would have been to connect the -1900V electron multiplier
> supply, feed in a 9.192632 GHz signal from an HP 8672A which would be
> frequency-modulated with a slow sawtooth, and watch for an output signal on
> a scope with a high-Z opamp buffer.  Unless there is some kind of sequencing
> taboo that says "bring up the electron multiplier before the ionizer", I
> don't immediately see what I might have done wrong.  Anyone see any obvious
> newbie mistakes in the account above?  Or was it just a matter of expecting
> too much from a Cs tube that might have been 20 years old?
>
> For what it's worth, the electron multiplier also shorts out its (negative)
> supply now.  I don't know if that would've happened earlier, since I never
> tried to energize it during the pre-test checkout.
>
> -- john, KE5FX
>   
John

Perhaps everything is now coated in Caesium, especially the electon
multiplier input dynode insulation??

Bruce

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[time-nuts] Thoughts on Cs tube failure modes

[John Miles]

I recently found a tube from a 5062C on eBay in unknown condition for not
*too* much money, and thought it would be interesting to power it up on the
bench.  Once I got it and saw the 19xx-prefix serial number, I wasn't too
optimistic, since it could potentially be 25 years old or more.  Things went
well for the first few steps of the process, but then the experiment failed
big-time.

1) I first applied +2600V to the ion pump with nothing else connected.  Spec
is < 10 uA.  There was a brief spike to ~100 uA, but within a few seconds,
the current began to drop rapidly, ending up at about 1 uA after a few
minutes.  So far, so good.

2) I then brought the Cs oven up to temperature slowly with a variable
supply.  The 5062C runs its oven in a thermostatic loop, but it was easy
enough to warm the oven up slowly over 10 minutes or so, watching the
thermistor resistance to achieve the 200-ohm reading indicated on the tube
label.  The ion pump current rose to about 2.5 uA during the Cs oven warmup
process.

3) I then attempted to bring up the hot-wire ionizer, which takes 1 volt at
about 1.6 amps (when hot).  Simultaneously, the 22-mA C-field current and
13.9-volt mass-spec supply was applied.  As with the Cs oven, I brought the
ionizer voltage up slowly.

4) At that point the ion pump supply went into full current limiting at
circa 300 uA.

I killed the power quickly, removed the oven and hot-wire ionizer supplies,
and tried powering the ion pump up by itself once again.  Although a DMM
check indicated infinite resistance across the ion pump, the HV supply still
went into current limiting.

I'm guessing that the hot-wire ionizer element had enough crud on it to kill
the vacuum when it vaporized.  The tube envelope is probably OK, because the
ionizer wire itself didn't burn out.  Unfortunately I was watching only the
hot-wire ionizer current during that part of the process, so I don't know if
there was a point where I could have observed a rise in ion pump current and
backed off in time to avoid permanent damage.

The last step would have been to connect the -1900V electron multiplier
supply, feed in a 9.192632 GHz signal from an HP 8672A which would be
frequency-modulated with a slow sawtooth, and watch for an output signal on
a scope with a high-Z opamp buffer.  Unless there is some kind of sequencing
taboo that says "bring up the electron multiplier before the ionizer", I
don't immediately see what I might have done wrong.  Anyone see any obvious
newbie mistakes in the account above?  Or was it just a matter of expecting
too much from a Cs tube that might have been 20 years old?

For what it's worth, the electron multiplier also shorts out its (negative)
supply now.  I don't know if that would've happened earlier, since I never
tried to energize it during the pre-test checkout.

-- john, KE5FX


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