Re: [time-nuts] Achieving maximum performance when driving 5370A/B inputs

[jimlux]

Mike Feher wrote:

In general, what about the old National "damn fast" and super damn fast"
LH0032 & LH0033? I used to use a lot of those in my designs many years ago.
- Mike



Gotta really decouple the power supplies on those puppies...


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Re: [time-nuts] Achieving maximum performance when driving 5370A/B inputs

[jimlux]

Bob Camp wrote:

Hi

Sure never seen any of them on any gear in my junk pile.

I also never seen a customer ask for them as an output connector on an 
oscillator. I wonder how common they actually are.

Bob


On Feb 27, 2010, at 9:59 PM, Bruce Griffiths wrote:


Actually there are miniature twinax style connectors, for example:
http://www.amphenolrf.com/products/twinbnc.asp?N=0&sid=4B8860805409E17F&; 


Bruce

Bob Camp wrote:





There's a variety of these kind of things.  You see them in 
MIL-STD-1553B systems, among others. Triax is also fairly common as a 
connector for "shielded twisted pair".  There are also twisted pair 
inserts for the DB-25 sized shell (actually a quad pair with 4 inserts).


The one that has one pin and one socket on each side is a much better 
strategy than the one that has 2 pins on one connector and 2 sockets on 
the other.


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Re: [time-nuts] nubie querie

[jimlux]

Paul Boven wrote:

Hi Tom, everyone,

Tom Van Baak wrote:

See: http://www.leapsecond.com/museum/pulsar for some
pulsar ADEV stability plots and links to many research papers
with all the details.


Your page starts with the question "if it was possible for an amateur to
receive pulsar signals?". Turns out you can, at least the particular
bunch of amateurs who have been restoring the 25m Dwingeloo radio
telescope (http://www.camras.nl).


This, and similar impressive accomplishments, has prompted some 
lunchtime discussion at work (JPL).. One of us (N5BF) has been 
contemplating what it would take to do an amateur EarthVenusEarth (after 
some of his experiments doing EME with 5 watts)..


So, when talking about "amateur" accomplishments.. where do you draw the 
line on using "big stuff".  If you're an amateur who happens to have 
access to Arecibo or to a DSN 70m dish, is that *really* an amateur 
contact/event?


The same thing applies to timenuttery, to a certain extent.

So we thought.. if it's something that a single amateur can feasibly do 
single handedly.  Surely, no amateur is going to build Arecibo or a 70m 
dish in their backyard.. but wait, what if you're Paul Allen building 
the ATA at Hat Creek.  Should happening to be wealthy enough to buy all 
the toys exclude you.. after all, it's the "amateur" aspect, not the 
"poverty" aspect.


Or, maybe it's the "fabrication" of the equipment that's the relevant 
thing.  I know I'd be more impressed by someone building a Cesium clock 
from scratch in their garage more than just buying one off the shelf, 
even if buying one is cheaper.  Kind of like making your own vacuum tubes.


And, even, since those of us sitting around the lunch table do RF work 
of one sort or another for a living, is *anything* we do with RF truly 
amateur (leaving aside legalisms like pecuniary interests, etc.).


Maybe it's a sort of fuzzy definition.. you can fit it in a suburban 
backyard (leaving out the 70m dishes, but not the EME array, as long as 
you're not in the W5UN category)


Or time nuts wise, some aspect of self fabrication, whether it be 
hardware, software, or even just an unusual configuration or kind of clock.





Could you do this with a more modest antenna? The lesser gain would need
to be compensated for by using as much bandwidth as possible (which
needs de-dispersion), and folding the signal by the pulsar period.
Folding in turn requires a stable clock, and compensating for the
doppler shift caused by the Earth's motions. I would say that receiving
the brightest pulsars is within reach of the bigger EME stations - but
still working on the calculations (and demonstration) to back this up.


This is kind of fascinating...  When I got started in home time nut 
territory, it was because I got a Z3801.. as a coworker put it, how 
often do you have something accurate to way better than a part per 
billion in your garage.







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Re: [time-nuts] Thermal Time Constant

[jimlux]

Brooke Clarke wrote:

Hi Bruce:

What does m2K/W mean?  See:
http://building.dow.com/europe/uk/proddata/styrofoam/thermal.htm

50 mm it's about 1.5 and for 100 mm it's about 3.



thermal resistance (you can tell because it's degrees/watt, as opposed 
to watts/degree which would be conductivity)


square meter Kelvin/Watt.

and doubling for a doubling in thickness makes perfect sense.




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Re: [time-nuts] nubie querie

[jimlux]

Hal Murray wrote:

This, and similar impressive accomplishments, has prompted some
lunchtime discussion at work (JPL).. One of us (N5BF) has been
contemplating what it would take to do an amateur EarthVenusEarth
(after some of his experiments doing EME with 5 watts).. 


Perhaps a better question is:  What is the bandwidth?

What sort of signal do I have to receive in order to claim contact?  Is one 
bit/blob of energy at the right time/frequency good enough, or do I have to 
demodulate the signal and extract a few bits of data?




So, when talking about "amateur" accomplishments.. where do you draw
the line on using "big stuff".  If you're an amateur who happens to
have access to Arecibo or to a DSN 70m dish, is that *really* an
amateur contact/event? 


I think the traditional test for an amateur is do you get paid for it.  (Yes, 
it helps to be independently wealthy.)


Well, that's sort of the 18th/19th century model, certainly.  Lavoisier 
wasn't paid to figure chemistry out. Neither did John Strutt, 3rd Baron 
Rayleigh.  But is that an appropriate model for today?




Even if you build your own antenna, there is the question of where do you 
start.  Is it OK to buy a dish if I build the mount?  Can I buy steel pipe or 
do I have to start from iron ore?


I've always wanted to start with smelting, but my wife says "no cupola 
furnace in the backyard"  (this after I was pointing out the books on 
this in the Lindsay Books catalog).





I suspect if you look at other amateur activities (say sports), there are 
examples equivalent to scrounging time on Arecibo.


Sure.. and the sponging off others has historical precedent, for 
DXpeditions and 8000 meter peak attempts alike.





My 2 cents...  You get credit for the part that you do.  Anything goes as 
long as you are honest about what you do.  If you buy the electronics and 
build the antenna, you get credit for building the antenna.  If you build the 
electronics and buy (or scrounge) the antenna, then you get credit for the 
electronics.  ...


Some people are really good at scrounging.






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Re: [time-nuts] Thermal Time Constant

[jimlux]

Brooke Clarke wrote:

Hi Bruce:

If a square meter of Styrofoam is 1.5 deg C/W then a cubic inch would be 
39.37 * 39.37 * 1.5 or 2,325 deg C/W


The DS3231 dissipates about 1 mw when running.  I'm not sure how to come 
up with an allowable temp increase, but suspect it's based on not 
exceeding the max allowed operating temp.  But for this part the Temp 
vs. freq curve is flattest at room temp so best to minimize the temp rise.

So:  (1 deg C) / (0.001 W) = 1000 deg C/W, the same number you had.

That requires 185 g of Aluminum or about 69 cc volume or 4.25 cubic 
inches.  That's a block about 1.62" on a side.


How does that look?




you can also use U.S. R-values..  BTU/hr/ft^2/deg F.

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Re: [time-nuts] Thermal time constant

[jimlux]

Bob Camp wrote:

Hi

The gotcha is that you are interested in the amount of heat per cubic foot rather than the amount of heat per pound. You need to take the standard heat per weight numbers and convert them to heat per volume numbers. 

Of the things you can easily get, copper is good. Steel is not as good as copper, but better than aluminum. 


Bob




Gold is your friend. Mercury has convective losses because it's a 
liquid.  Platinum or Osmium would also be ok.


You might want something that is dense but lower conductivity.. lead? 
Depleted Uranium? (DU is available very cheaply if you can take 80,000 
pound lots)


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Re: [time-nuts] FE-5680A

[jimlux]

Bob Camp wrote:


My personal experience suggests that setting one up is indeed a black art known 
only to the select few. The high priest takes them into the back room and they 
magically come return in working order several days / weeks / what ever later.  
High priest goes on vacation - not much is going to ship 

Bob

There are still many high-tech products which fit in this general 
description.  Adjusting tunable filters, Focusing TWTs using permanent 
magnets, etc.


at lunch today, someone was talking about a guy from RS Microwave 
commenting that they had fooled with automatic filter tuning by 
computer, but a "good" tech could beat it every time. the machine tuning 
worked great for a specific filter, so if you had a big production run, 
it was ok, but if you're building just a few of each filter.


(I rummaged in Google and found
http://www.ee.ntu.edu.tw/news/96-Snyder-Filter-Development.pdf
)

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Re: [time-nuts] nubie querie

[jimlux]

J. Forster wrote:

If you like starting from scratch, get a copy of "Procedures in
Experimental Physics" by John Strong.

-John




And, relevant to the thermal time constant discussion.. That book has a 
great section on thermal diffusion and conductivity, along with a chart 
of material properties.



A newer book is "building scientific apparatus" by Moore, et al. 
There's a whole section on precision temperature control (where 
precision means milliKelvin)..


But not as much fundamentals stuff as in Strong. e.g. Moore assumes you 
can buy a vacuum pump, Strong tells you how to build one..what a 
difference 60 years makes.


But even Strong doesn't tell you how to make cast iron from ore. 
Lindsay Books is your friend, then.


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Re: [time-nuts] Thermal time constant

[jimlux]

Predrag Dukic wrote:



How well depleted it really is? 


DU has about 1/3 the U235 of  natural U, of which less than 1% is U235. 
 All the isotopes are radioactive, but I don't recall what the relative 
activities are.  I think U238 has a half live of 4E9 years or more, so 
not very many atoms spontaneously disintegrate every second.


 Uranium separation is not perfect. Some

radioactivity is still left.


Not much.. you'd have more trouble if you lived on granite or lived in a 
brick/stone house.


It's an alpha emitter, too, so painting it would provide shielding. 
It's the fact that it's a heavy metal that's more of an issue for toxicity.

Don't know about the neutrons from the spontaneous fission.




I don't think it is healthy to have it beside You for a long time.

Certainly not 8 pounds :))






At 05:35 11.3.2010, you wrote:

Bob Camp wrote:

Hi
The gotcha is that you are interested in the amount of heat per cubic 
foot rather than the amount of heat per pound. You need to take the 
standard heat per weight numbers and convert them to heat per volume 
numbers.
Of the things you can easily get, copper is good. Steel is not as 
good as copper, but better than aluminum.

Bob


Gold is your friend. Mercury has convective losses because it's a 
liquid.  Platinum or Osmium would also be ok.


You might want something that is dense but lower conductivity.. lead? 
Depleted Uranium? (DU is available very cheaply if you can take 80,000 
pound lots)


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Re: [time-nuts] Choke Ring Pictures

[jimlux]

David C. Partridge wrote:

definition of "pie"


3.1415926535 etc ? 


Ooops
D.



And, as my daughter reminds me, today is pi day (in the U.S. where we 
write the date month/year.. those of you in the rest of the world will 
have to wait a long time, as there is no April 31st)


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Re: [time-nuts] Choke Ring Pictures

[jimlux]

Bob Camp wrote:

Hi

Machining a chunk of Plexiglas sounds like more trouble that I would want to go to for a cheap choke ring setup. 


Maybe a hemispherical Plexiglass serving bowl 



take a look at inexpensive light fixtures with hemispherical or 
spherical plastic globes.


Actually, hemispheres are made by softening the acrylic or polycarbonate 
or styrene sheet over a round hole, and then pulling a small vacuum on 
it (a vacuum cleaner is more than enough).


Pretty easy to do at home.. sheet of plywood or particle board with the 
right sized hole in it, some heat lamps (or a steady hand with a moving 
propane torch and flame spreader)


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Re: [time-nuts] enclosure temperature controllers

[jimlux]

Don Latham wrote:

hello the group:
I've just installed a new "mercury-free" thermostat in my shop. I looked
the thing over and realized it has everything needed to control a
"constant temperature" enclosure. There's a diode used as temp sensor,easy
to remote with two wires, a place to put two AA batteries, a pot to adjust
the set temperature, all needed circuitry for a bang-bang controller with
1deg F hysteresis, uses a latching relay so the batteries last a long
time, a low battery indicator, and an easily backengineered circuit board,
and a low price. There is provision for external power as well. The one I
bought is a rite-temp model 6005; distributed by home despot. And it's
relatively cheap, about 20 devalued rasbuckniks. All that's required is
whatever needed for a heater and its power supply. Unfortunately, not for
110 volts but I didn't look at the relay to get the capability; that may
be a lawyer problem rather than a capacity problem.
Don

probably runs on 24VAC... a "doorbell transformer" is what you need. 
They're current limited.  Then, a couple 12V lightbulbs or a suitable 
resistor as a load.


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Re: [time-nuts] frying pan antenna

[jimlux]

Bob Camp wrote:

Hi

I certainly won't disagree with the data. I have noticed over the years that past a few MHz antennas out in the fresh air always seem to work better than indoor antennas. It could easily be that there is a *lot* of water in your typical roof. Certainly the water is far from pure, so it's going to be pretty low conductivity. 


Bob



there's also an amazing amount of metal and other junk in the usual 
composition roof construction.  Nails to hold the shingles on, for instance.


But I think the major absorption will be the moisture in the wood sheathing.

By this logic, a thatch roof in a dry climate is the best thing going.


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Re: [time-nuts] frying pan antenna

[jimlux]

Bruce Griffiths wrote:

Mike

Perhaps a single antenna element from the phased array in the following 
JPL paper would be useful:

http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/12178/1/01-0082.pdf



I don't know that Mark's antenna is the right kind of thing for GPS. 
the x-pol off axis is pretty high and the construction is dependent on 
having the right materials around.  You could probably use a HDPE 
cutting board instead of teflon and some other foam.


If you want gain in the vertical direction, why not a stacked patch with 
air dielectric?


Mark's antenna in the article was eventually intended to be for a
"phased array at the focus of a reflector/reflectarray" application in 
space, so fabrication of a stack was more appropriate.



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Re: [time-nuts] frying pan antenna

[jimlux]

mike cook wrote:

Yes Bruce, I also think that azimuth dependent masking would be useful.

I have been suffering from strong reflections from facing buildings at 
50m to 100m, which cause sharp departures from the average PPS TI 


While telling the nav algorithms inside the box would be the most clever 
way, you could also put up a fence of RF absorber (or perhaps even 
conductive sheet) at some distance from the antenna.  The wavelength is 
on the order of 25-30 cm, so a fence a couple meters away is in the "far 
field"


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Re: [time-nuts] Missing GPS satellites

[jimlux]

Jeffrey Pawlan wrote:

On Thu, 25 Mar 2010, Magnus Danielson wrote:


Dear Raj,
Oh, sorry, needed a few extra. Wanted to recover the rubidiums and put
some on Ebay.





I gave a lecture about antennas for operation on 1296MHz last week and 
mentioned that my vacuum tube power abplifier was damaged by a gassy 
tube. I want to replace it with a solid state amp.  One of the engineers 
present suggested that I find a GPS satellite on the surplus market and 
pull the the power amplifier out of it.


He obviously did not know that satellites , even spares, do not show up 
on the surplus market.




Things like that DO show up as surplus but I wouldn't call it a market. 
When we excess things at JPL (and that includes spare flight hardware), 
it goes on a list, and other NASA centers, and then gov't agencies, and 
then universities/colleges/educational institutions get a crack at it. 
Finally, it will get scrapped.


There is also the ITAR and export controls issue.  (an interesting 
question I'll have to ask... if you have a rad hard widget for a 
spacecraft (clearly ITAR), and you surplus it in a way that makes it 
impossible to know it's Class S, is it still controlled..)


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[time-nuts] connectors Re: FW: Re: Low-Cost 6+ GHz Prescaler board for

[jimlux]

John Allen wrote:

A few notes about the connector.

First, I hate BNC connectors.

But the BNC is useable to 11 GHz (No vswr spec.), and has a VSWR spec. of 1.3:1
up to 4 GHz.  (See link below, about half way down the page.)
http://www.amphenolrf.com/products/bnc.asp?N=0&sid=4BAAA780568BE17F&;

The application is not a precision one except for frequency - Power transfer
inaccuracy due to return loss is not a big deal here, we are not using it in a
VNA or power meter etc.  


PS: Would anybody be interested in testing an SMA to BNC-F and BNC-M to SMA pair
on a VNA?

Further, some BNC adapters (to SMA) are specified. to 8 GHz. With 1.25:1 VSWR
Also - here is a BNC to SMA bulkhead with 10 GHz VSWR max of 1.4:1
http://www.fairviewmicrowave.com/adaptersbncsma.htm (Bottom middle).

Now if only we could find a SMA to SMA bulkhead that fit in a BNC mounting
hole...

John Allen K1AE
 



I think I've seen hermetic sealed feedthrough for applications like 
vacuum chambers that fit in a larger than normal hole.  But they're 
probably also really, really expensive.


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Re: [time-nuts] Anritsu MH-4100A xtal osc (Pete Lancashire)

[jimlux]

Dave Baxter wrote:

This might interest you
http://www.members.shaw.ca/swstuff/gpsreference.html

These people can cal' it, they say.
http://www.raelectrical.com/services/anritsu-2.htm

There are several other hits, including other people who stock used
items.

Amazing what you find when you google

My guess is in it's original form, it's a small lab standard,
calibrateable, and no doubt intended to be powered on 24/7 for
stability.

Even where absolute accuracy is not needed, a common frequency reference
for multiple instruments is often desirable, especialy where there are
sources and measuring instruments used for a common task, so as to
minimise differences between them.




Oh yeah.. there's always the discussion at work about whether you use 
the internal 10 MHz from the counter or the internal 10 MHz from the 
signal generator as the "master" for your setup.


The counter typically has better accuracy over the long term, but the 
signal generator usually has better close in phase noise.


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Re: [time-nuts] Surplus Places...

[jimlux]

Scott Burris wrote:

C&H closed briefly to move and is now open in Duarte:

http://www.candhsurplus.com/

At Apex, a friend tried to purchase a nose cone from a rocket, but they declined
to sell it to him because they were making too much money renting it out to 
movie studios.

Scott




That is precisely the reason for outrageous prices at Apex.  If it makes 
 a good prop (spinning mag tape drives, panels with lots of switches 
and lights, etc.) then they can make hundreds of dollars a week in rental.




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Re: [time-nuts] Surplus Places...

[jimlux]

Rex wrote:

jimlux wrote:

Scott Burris wrote:

C&H closed briefly to move and is now open in Duarte:

http://www.candhsurplus.com/

At Apex, a friend tried to purchase a nose cone from a rocket, but 
they declined
to sell it to him because they were making too much money renting it 
out to movie studios.


Scott




That is precisely the reason for outrageous prices at Apex.  If it 
makes  a good prop (spinning mag tape drives, panels with lots of 
switches and lights, etc.) then they can make hundreds of dollars a 
week in rental.




Maybe, I don't hang out in LA land much.

I went somewhere once and am pretty sure it must have been Apex - had 
the same random back yard. I found a couple big-ass bearings, close to 3 
inch ID. I had some project in mind and they gave me a reasonable price, 
maybe $5 each, So, lots of stuff is over priced, but maybe if you browse 
a while, you may find some stuff that can be negotiated at a mutual 
advantage.




that's exactly it...no art director or set decorator is wandering 
through Apex saying "I wish I could find some 3" bearings"... they're 
wandering going "I need 3 of those big tall panel things with the blinky 
lights", and the Apex guys, say, no problem.. we'll deliver them to the 
set tomorrow for $100/week each.


So your bearings are cheap. Rocket nose cones are not.

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Re: [time-nuts] Surplus Places...

[jimlux]

saidj...@aol.com wrote:
Back in the days (around 1985 or so) Caltech in Pasadena used to have a  
surplus store on campus. I spent a good time in that store, and still have 
some  of those treasures. Lot's of JPL stuff.
 
Does anyone know if that still exists??
 



No. doesn't exist.

Most government facilities (including JPL, which although part of 
CalTech, all the property is owned by NASA, so for surplus situation is 
government) have to dispose of their excess inventory in a special way. 
First you put it on a list, then other NASA centers get to pick and 
choose, then, other gov't agencies, finally educational institutions, 
and, then, only then, is it put up for bid, and then, someone could buy 
it and sell it at retail.


For the most part, I think it all gets bought as metal scrap, is crushed 
and shredded and then loaded on ships for recycling elsewhere.


I think there's a lot of factors leading to the demise of surplus stores...
1) Hazmat disposal rules - cradle to grave responsibility makes 
disposing institutions concerned about inadvertently having something 
hazardous in the pile of junk.  Transfer to someone who is ostensibly an 
entity willing to accept liability, do the paper work, etc.


2) A huge overseas market and cheap transportation - it's economically 
worthwhile to grind up broken whatevers and extract the metals by acid 
leach, particularly if this can be done in a place without many 
workplace safety regulations and low wages.  (I don't say it's ethically 
right, but it is clearly advantageous in economic terms. I think the 
practice is reprehensible. )


3) ITAR and export controls - if you're not just going to grind 
everything up, then you have to make sure that you're not surplusing 
something that is export controlled.  The laws are vague and scary in 
consequences.  Is it worth spending time examining each piece of gear 
and deciding whether it might be a "defense article" or "dual use"?  How 
many surplus places are set up to deal with that?


4) For test equipment, the rise of the equipment rental industry. Fewer 
large companies actually own any test equipment these days; they rent or 
lease it, and the rental companies don't seem to feed the surplus market 
in quite the same way.


5) Manufacturing and equipment processes have changed. Fewer piece 
parts, less hand assembly, so you don't see surplus parts.  Much better 
estimation and planning, so less "surplus" (in the sense of buy 20% more 
to account for scrap and so forth, and actually wind up with 10% left 
over at the end of the production run)


6) Ebay and UPS.  I think that's more the death of things like ham-fests 
as supplies of equipment.  Why get up early, load all that stuff into a 
truck and take it to sit at a table in the sun all day, when you can 
(clad only in your underwear) put up the listings, receive the orders, 
box the stuff up, and have UPS pick it up at your front door. 
Interestingly, I see even this model fading, as the more organized 
surplus style places take over the marketplace.


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Re: [time-nuts] Surplus Places...

[jimlux]

Bob Camp wrote:

Hi

There have *always* been multiple tiers to the surplus market.
Catalogs of gear have always shown up with prices that were 10X (or
100X) what an item might be bought for. That was as true in 1965 as
it is today. A *lot* of those old time outfits lived off of a buy it
for < 1/3 list and sell it for > 2/3 list business model. Apparently
there have always been people willing to pay those sort of prices.


That's a useful niche. One of the advantages of C&H over, say, Apex, was 
that they had a catalog.  If you actually needed something (as opposed 
to wandering the aisles looking for stuff that might be useful: my 
garage is full of things like that), then it was worth it to pay the 
premium to have the fine folks at C&H sort and label things and put it 
out in a catalog.


When I was in the special effects business, the ability to run through 
the catalog and find an air cylinder or gear motor that would work, and 
then send someone over to buy it, was invaluable.





The "universal PC instrument" is a lot like those cute little "all in
one machines". Either you have a dozen of them each set up for a
single task or you spend time converting back and froth between
tasks. It's a drill press and I need a lathe ... It's an ohm meter
and I need a frequency counter 



I think a more modern model now is to have the standalone instrument, 
with the PC serving as the user interface.  Think of the USB based RF 
power meters. After all, a goodly number of instruments from Tek and 
Agilent now have an embedded PC in them (running Windows in some form), 
so it's just dividing the box at a different point.


The down side is that there are times when having a knob to twist is 
just nice (spectrum analyzers with a "frequency","span","ref level", or 
scopes with vertical gain, horizontal sweep and trigger).




Like the universal machine, once you do get it converted around, it's
not *quite* as good at any one task as a dedicated machine. Mass and
rigidity counts in machines ... self calibration only goes so far on
an instrument.

You can indeed get the task done either way. You'll get it done with
less hassle with the dedicated gear. You'll save money with the all
in one. There will be a market for both for a long time to come.

Bob





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Re: [time-nuts] lunatic fringe time standards

[jimlux]

Eugen Leitl wrote:

Hi -- a couple somewhat lunatic questions. Figured this would
be the best place to ask.

Anyone aware of a time standard which compensates in regards
to an ideal flat-spacetime-at-rest-relatively-to-cosmic-background
reference clock? I realize this is not relevant for any affordable
clocks.

Unrelated, anyone aware of a hardware (IC) counter which
counts in a (local-bitflip) Gray code, so it can track a very
fast (integrated?) oscillator without dropping cycles? 


Any synchronous counter won't drop cycles, right?  only ripple carry 
asynchronous have the propagation delay problem.


However, since long synchronous counters are complex, another way to do 
it is with a linear feedback shift register (LFSR).  Rather than doing 
it as usually drawn, with taps all getting xored to generate the single 
feedback, you do it using the output and feeding it "into" the stages 
(with an Xor) where the taps are.







P.S. Thanks for pointing me towards GPSDOs. Any European/German
local alternatives to the Trimble Thunderbolt?




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Re: [time-nuts] lunatic fringe time standards

[jimlux]

Bob Camp wrote:

Hi

The only real limit on a Johnson counter is how clever you get making sure
that only one stage is a 1 and all the rest are zeros. There are *lots* of
ways to take care of that, each with it's own set of trade offs. 



One problem with a Johnson counter is that it takes many more flipflops 
for a given number of states.  you get 2N states from N stages.


Compare to a standard binary counter where you get 2^N states from N 
stages, or a LFSR, where you get 2^N-1 states.


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Re: [time-nuts] lunatic fringe time standards

[jimlux]

Bob Camp wrote:

Hi

The only real limit on a Johnson counter is how clever you get making sure
that only one stage is a 1 and all the rest are zeros. There are *lots* of
ways to take care of that, each with it's own set of trade offs. 


Bob



Of course, if your goal is "minimizing gates" or "minimizing 
transistors", particularly if you need 1 out of N decoding.. a 
ring/Johnson counter might be a better strategy than a smaller counter 
with lots of states and more complex decoding.


But, if "counting" or "addressing", then standard counters or LFSRs are 
better.  The LFSR with multiple feedback is nice because every stage is 
identical.



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Re: [time-nuts] [OT] degausing

[jimlux]

wa1...@att.net wrote:
FWIW.A good high quality compass needs to be designed based on what 
region of the earth you plan to use it in. The Suunto ones I have are 
marked with a US region code.





That's because they need to compensate for the "dip" in the magnetic 
field.  The south end of the needle in the US is weighted heavier so the 
needle sits level.


The magnetic field is so non-horizontal in some areas that there are 
stories about making permanent magnets by heating iron bars in a 
fireplace and standing them up next to the fireplace to cool.



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Re: [time-nuts] [OT] degausing

[jimlux]

Chuck Harris wrote:

David Martindale wrote:


However, I don't see how the earth's tilted field prevents a CRT from 
being

used in both hemispheres.  I can see how it might need to be realigned,
since it uses permanent magnets on the yoke and their field will be
influenced by the earth's local field.  But a different model for the
southern hemisphere?


It has to be made somewhere, and if that somewhere has a magnetic field
that points in the opposite direction, of where the CRT is going to be
used, it is going to be aligned wrong.  The answer can be as simple as
readjusting the magnets on the CRT.

The real solution is to put the CRT in a magnetic shield.

-


And, of course Trinitron tubes, since they have only one gun, no 
shadowmask, and synchronize by looking for the backscatter from the 
face, are immune to such convergence effects.


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Re: [time-nuts] [OT] degausing

[jimlux]

Chuck Harris wrote:

Are they really?  For some reason, every Trinitron I have ever seen
has clusters of little stick on magnets placed here and there on the
back of the glass envelope.

The trinitron has a shadowmask.  It is a grill of highly tensioned wires
that are positioned just behind the screen.  The original trinitron tube
was a little 5 inch diagonal CRT.  It had to be small because the wires
tended to vibrate if the set was bumped, and that made for some very odd
displays.  The later larger tubes had horizontal titanium wires welded to
the backs of the shadow mask wires every 5 or 10 inches, to prevent the
psychedelic color fest that happened when the CRT got bumped.

The trinitron has three very carefully aligned cathodes in the gun.  They
are positioned side-by-side, creating the slight different projection
angles necessary to cause the long vertical slots formed by the shadow mask
to eclipse the appropriate color bands on the screen.

I'm not sure what you are describing; it sure sounds cool; but it isn't
a trinitron.

Can you find some references?  I'd like to read up on it.




You're right...
I must have been thinking about another scheme.. Now I'll have to go 
find it.


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Re: [time-nuts] lunatic fringe time standards

[jimlux]

Rob Kimberley wrote:

Am I really that old?!!?

:-)

-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Chuck Harris
Sent: 19 April 2010 10:10 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] lunatic fringe time standards

Here is a link to a datasheet for the uL923:




And you can probably still buy 709 and 714 op-amps..


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Re: [time-nuts] lunatic fringe time standards

[jimlux]

Arthur Dent wrote:

jimlux-"And you can probably still buy 709 and 714 op-amps.."

I'm old enough to know that it is 741 op-amps, not 714. ;-)



Ooops..
it was early in the morning

And for the life of me, I cannot remember the number of the comparator 
in the 7xx series.. contemporaneous with the 709.


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[time-nuts] venerable ICs was Re: lunatic fringe time standards

[jimlux]

Bob Camp wrote:

Hi

The ua723 obviously is the one destined to outlive the cockroaches. The
linear power supply industry still seems to consider them "state of the
art".

Bob



Like the 555, it has a nice combination of function and predictability. 
 It's in that "good enough" category.



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Re: [time-nuts] GPS 1 PPS accuracy limits

[jimlux]

life speed wrote:

Time Nuts;

I have a customer request for a microwave frequency synthesizer with
extreme accuracy requirements; 4 X 10^-11, or 0.04 PPB.  Obviously
this is way out of quartz oscillator territory.  Is GPS 1
pulse-per-second useable, or do they need an atomic clock?  Maybe
they don't realize what they are spec'ing.




Do they have other requirements (Allan deviation? phase noise?)

Over what time span do they want 4E-11 accuracy? 1 second, 1000 seconds, 
days?


A synthesizer locked to a Stanford Research PRS10 (datasheet accuracy 
5E-11) is in that ballpark.


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Re: [time-nuts] oscillator choice question

[jimlux]

Hal Murray wrote:

bruce.griffi...@xtra.co.nz said:

If there is no electronic tuning available one can use a DDS based
synthesiser to produce a corrected output frequency. However close in spurs
will be problematic unless one use a couple of  simple mix and divide stages
or resorts to a Diophantine synthesiser  using phase noise truncation spur
free output frequencies from the DDS  chip(s). 


I think I understand the classic spurs from a DDS.

I wasn't familiar with Diophantine techniques.  Google found this
  http://www.hindawi.com/journals/ijno/2008/416958.html
which is readable at my level.

But I don't think I understand the big picture.  The example numbers they 
give involve mixing 500 Hz with 10 MHz.  Assuming I want the sum, how do I 
get rid of the difference?  It's going to be a good strong signal, as strong 
as the one I want.  I think anything that leaks through the filter into the 
next mixer is likely to make mirror sidebands that are right where we don't 
want them.


Why is that going to be easier to get rid of than traditional spurs?




Alternatively if one implements the DDS in an FPGA its possible to
virtually eliminate such spurs using a modified algorithm. However this
requires an external DAC to produce the required output. 


Got a URL?  What's magic about a FPGA?  Why don't traditional DDS chips use 
that modified algorithm?







Commercial DDSs are sold in large quantities for generalized 
applications, so they tend not to use exotic techniques for spur 
reduction over small ranges. You can also burn gates in exchange for 
performance, a decision that would be tough to make for a manufacturer 
concerned about power dissipation, etc.


 It's easy, for instance, in a FPGA, to implement several different 
length cosine lookup tables, so that all the frequencies you want to 
generate exactly match the table length.  You can also do things like 
error filtering, various spur cancellation techniques, etc.




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Re: [time-nuts] Simple PLL chips, gone ?

[jimlux]

Luis Cupido wrote:

Hi,

I'm looking for a relatively simple PLL chip
like LMX1501 or similar.

I mean, looking for a new design, that is something
that is easy to source (known to be in production etc)
recent/modern enough to provide a low phase noise.

Is for VHF/UHF below 500MHz application and will
be for MHz steps (no small steps required).
Albeit reasonably low phase noise will be wanted.


What seems to be available from An.Dev. and Nat.Sem.
are way too unnecessarily complex and I would like
it to not have a zilion registers to load via spi.
(might use just a small corner of a CPLD to load it).

Are the simple ones gone obsolete, or simple no longer in the
web pages ???

ok... I think you got the idea...
I'm looking for the basic think...

Any suggestions of what might be usable/available.



How about the Peregrine 9701?  Pretty low noise, simple (20 bit serial 
word to load).. Max reference divider is 63 or 64.


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Re: [time-nuts] Simple PLL chips, gone ?

[jimlux]

Luis Cupido wrote:

Hi,

I'm looking for a relatively simple PLL chip
like LMX1501 or similar.

I mean, looking for a new design, that is something
that is easy to source (known to be in production etc)
recent/modern enough to provide a low phase noise.

Is for VHF/UHF below 500MHz application and will
be for MHz steps (no small steps required).
Albeit reasonably low phase noise will be wanted.


What seems to be available from An.Dev. and Nat.Sem.
are way too unnecessarily complex and I would like
it to not have a zilion registers to load via spi.
(might use just a small corner of a CPLD to load it).

Are the simple ones gone obsolete, or simple no longer in the
web pages ???

ok... I think you got the idea...
I'm looking for the basic think...

Any suggestions of what might be usable/available.


Thanks.

Luis Cupido
ct1dmk.




Or Fujitsu  (e.g. MB15E03SL)

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Re: [time-nuts] Simple PLL chips, gone ?

[jimlux]

Nick Foster wrote:

If you're thinking about using a CPLD to load registers in a PLL chip, why not 
just implement the PLL on the CPLD? After all, if you're looking for 
simpler-is-better, there's not much on a dedicated PLL chip that you can't 
easily replicate in CPLD with some care and attention paid to layout.




Most CPLDs don't have low noise phase frequency detectors, the charge 
pump,  or the analog parts to make the loop filter.


Jim

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Re: [time-nuts] synchronizing a large number of weakly coupled oscillators

[jimlux]

Eugen Leitl wrote:

Has anyone utilized a network of locally, weakly coupled
oscillator synchronization (a la 
http://www.projectcomputing.com/resources/sync/index.html )
for precise timekeeping purposes?

There was a discussion on this list about doing something like filling a 
cavern with pendulums in this connection a couple months ago.


Bob York at UCSB and Ron Pogorzelski, a recently retired colleague of 
mine at JPL, hav done a lot of work with coupled oscillator arrays. 
They're used as a way to do phased array antennas.  googling "coupled 
oscillator array" will turn up many hits.


Allan had a paper where he had 8 inexpensive crystals coupled with 
mixers and a microcontroller.  I think it's called the Clever 
Temperature Compensated XO or something like that.


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Re: [time-nuts] synchronizing a large number of weakly coupled oscillators

[jimlux]

Bob Camp wrote:

Hi

The tendency of clocks to self synchronize dates back at least to the
days of pendulum clocks. It may date to the era of water clocks, but
if so it's undocumented. It has been observed on a wide range of
modern clock designs. If you look into "injection locking" you'll get
a pretty good picture of what's going on.




Oooh.  Clepsydra  (is that also the plural?).. one of my favorite topics..

It never occurred to me that they might couple, although almost every
other mechanical clock does.

What would the mechanism be?
How could one set up an experiment?

(hey, it's getting to be summertime, and my kids need projects that 
might get them wet)


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Re: [time-nuts] synchronizing a large number of weakly coupled oscillators

[jimlux]

Eugen Leitl wrote:

On Wed, May 12, 2010 at 06:03:11AM -0700, jimlux wrote:


Allan had a paper where he had 8 inexpensive crystals coupled with 
mixers and a microcontroller.  I think it's called the Clever 
Temperature Compensated XO or something like that.


Presumably, a large population of cheap coupled oscillators could be
rather accurate collectively.



I think that there's a point of diminishing returns.. the uncertainties 
in the coupling start to dominate over the reduction in uncertainty from 
combining multiple clocks.  one of those N vs sqrt(N) sort of things.


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Re: [time-nuts] (no subject)

[jimlux]

Rex wrote:

Sorry about the empty post -- hit the send key by accident.

Ulrich's free Z38XX program works great as a monitor for the Z3805. He 
added some stuff to specifically support differences from a Z3801. The 
Z3801 programs can be used but can't support the extra satellites the 
3805 can track.


Available here: http://www.ulrich-bangert.de/html/downloads.html

The lower 25-pin connector is the serial port you want to connect your 
PC to. Someone mentioned 488; I think that is only on Z3801's. My Z3805 
has a serial interface on the lower 25-pin connector.




On the 3801 (and probably the 3805, those who know can correct me) there 
are some jumpers inside that set the style of serial i/o: rs422 or 
rs232.  You should check to see which it is, before you hook it up.


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Re: [time-nuts] Z3805 utility, Was: AW: (no subject)

[jimlux]

Mike S wrote:

At 09:47 PM 5/22/2010, Robert Darlington wrote...

Was there ever a standard?  I always thought the "RS" stood for
Recommended Standard, as in "you *should* do the following" as


Recommended Standard, and is "this is a standard which is recommended 
for use."


The latest standard I've seen is ANSI/TIA-232-F-1977, Approved Sept 30, 
1997, Reaffirmed Oct 11, 2002.


The actual standard is obviously more involved, but basically the 
receiver should handle +/- 25 Volts. Anything between +/-3 is undefined. 
The transmitter should produce in the range +/- 5-15 Volts into 3-7 
KOhm. I believe the earlier RS-232C called for nominal +/- 12 Volts.




and any pin should source/sink 30mA

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Re: [time-nuts] Z3805 utility, Was: AW: (no subject)

[jimlux]

Bob Camp wrote:

Hi

The Symmetricom 3805's have an area on the lower board right behind
the "control" DB-25. It's very similar to the 3801. There are three
rows of holes for 0.025" post connectors. One row pair is labeled
RS-232. The other row pair is labeled RS-422. The original intent
appears to be to jumper the unit for what ever standard the customer
desired. 


Such was the case on my 3801.. 10 minutes work with a soldering iron and 
some wirewrap wire, and it was converted from RS-422 to RS-232.



It's not at all clear that the later units are even stuffed

for the RS-422 option. There are a number of unstuffed IC locations
on the pc board.

Your unit sounds like it's either blown, or running RS-422. I have
never seen one of the earlier HP 3805's so I don't really know how
much they have in common with the older units. There are indeed USB
to RS-422 converters out there that will run on a normal PC.


But unless you're running long wires, or happen to have a RS422 
differential system, why bother.  If all you're going to do is hook up 
the PC to check it out, RS232 is much easier to come by.




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Re: [time-nuts] Z3805 utility, Was: AW: (no subject)

[jimlux]

Robert Benward wrote:

Bob

Looking at al these pictures, I'm beginning to think I have a Z3801A, 
not a 05A.  After a few hours, the unit still has not locked.  It is 
possible the antenna is bad. I have a few more that I know are working.  
I also took the precaution of connecting an antenna before powering up, 
as  the manual says it will go into an extensive search mode if it can't 
find satellites.


Bob

it may go into extensive search mode regardless.. When was the last time 
it was powered on? How far did it move from where it was powered on to 
where it is now.  Mine seems to come back to life pretty quickly if it 
hasn't been moved and power's been off for a short time (a few weeks), 
but otherwise, if it doesn't get lock right away, it takes a *long* time 
to resync.  I think it waits to download a whole almanac, and then 
sequentially searches.  After all, "time to first fix" isn't a design 
goal for these things... they're on all the time.



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Re: [time-nuts] Z3805 utility, Was: AW: (no subject)

[jimlux]

Stanley Reynolds wrote:








Dec computers / terminal servers were as I described, but many brands
were different. Still have a BOB aka break out box with LEDs to
indicate levels, matching transmit and receive is easy, getting the
hardware flow control / signaling right was a little more difficult.


straight cable = pin to pin

crossed cable = null modem = swapped pins

The phrase "null modem" comes from no modems or the configuration
that allows two singular ports to be connected, this cable would
cross the receive and transmit pins, and some would call it a cross
over cable. A null modem cable would be used to connect two computers
together and a program like kermit used to transfer files.



Yep.. DTE cable to DCE communications medium(phoneline) DCE to DTE
DCE == Modem (e.g. a Bell 202 or 212, for instance)

There were the flow control (RTS/CTS) used to turn around a half duplex 
link.  And, there are also the secondary transmit and receive (for a low 
rate reverse channel).  If you were receiving data from the link (DCE), 
you'd assert RTS, and when the modem had switched, it would tell you 
CTS, and off you'd go.  (fancy modems used the reverse channel to send 
the request to the far end, which would acknowledge... others just use a 
fixed time delay)  There are also pins for the clock (since some of 
these modems were used on synchronous data links).


the "crossover" occured in the DCE to DCE link (that is, you'd transmit 
from one DCE to the other DCE's receiver)...


the nominal cable between DTE and DCE was straight through. With no real 
convention on male/female.. most devices had female sockets, and the 
cables usually were male male plugs.  IBM PCs had male on the chassis 
for DTE, as did some PDT-110 (VT-100/LSI-11 smart terminals), but most 
other terminals (the LSI ADM-x, Hazeltines, etc.) all seemed to have 
female, as did the TI 800 series printer/terminals.


So, a "null modem" was a cable that emulated the DCE to DCE connection..

there are/were various strategies on how sophisticated the reverse is.. 
do you also send the secondary channel?  What about clocks? Most folks 
ignored all that and used RTS/CTS


Or you strap RTS to CTS on your side, the other side does the same.







I think the phrase "standard cable" which could be null or straight
depending on the use  is the confusing part.

Phone cables RJ11 and RJ45 swap the wires which is standard.  Network
cables match the wires with the same color always on the right which
is standard. But even when a phone cable is standard it is not
interchangeable with a standard network cable. Again we have a need
for cross as well as straight network cables.



And, to make things worse, there are different "pair" arrangements.





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Re: [time-nuts] Z3805 utility, Was: AW: (no subject)

[jimlux]

Bob Camp wrote:

Hi

Gotta label them *something* or sorting through them in the cable bin becomes pretty difficult. 


In addition to the wiring options you can (obviously) have either a male or female on 
either end. There are so many "odd" pieces of gear out there that you can have 
pretty much any combination.

Bob




A while ago, I standardized on ALL straight through cables, M to F, and 
made "null modem" adapters.  So, now the bin has F:F and M:M widgets and 
F to F null modems in various flavors. I think I also still have a bunch 
of MFMF short cables made from ribbon cable and insulation displacing 
connectors (a sort of universal adapter).


Anyway, the key was having "null modem adapters" that are clearly 
identified as such, and everything else straight through.



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Re: [time-nuts] IRIG B

[jimlux]

Clive Green wrote:

Can anyone help with a modern IRIG B chipset manufacturer



I didn't know that there was such a thing, even in ancient times, much 
less modern.  All I've seen are designs made of discretes or programmed 
in a microcontroller or FPGA.


Are you looking for a IRIG generator or receiver.  DC or modulated on audio?

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Re: [time-nuts] IRIG B

[jimlux]

Hal Murray wrote:

Can anyone help with a modern IRIG B chipset manufacturer


Send or receive?

The ntp package has software for both sides using PC audio cards.



I've been looking for an open-source IRIG B or E reader for FPGA use.

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Re: [time-nuts] IRIG B

[jimlux]

Stanley Reynolds wrote:


Example of IRIG-B generator and decoder implemented in LabVIEW FPGA:

http://zone.ni.com/devzone/cda/epd/p/id/3396




Thanks,
I was looking for something in VHDL or Verilog... I'm not sure how well 
the Labview RIO, etc. stuff ports to non-Labview environments, but I'll 
ask some Labview gurus about this one.


Thanks again
Jim

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Re: [time-nuts] IRIG B

[jimlux]

Bob Camp wrote:

Hi

Audio codecs (especially monophonic ones) are pretty cheap these days.
Depending on volume they can get to the sub $1 range. Even in small quantity
they are below $4. That makes them a pretty tempting "front end" for a send
/ receive box.

Bob




i would think, given that the audio carrier is 1kHz-ish, that almost any 
of the small microcontrollers would work, using a single bit in/out with 
some RC signal conditioning.  Maybe a bit of a challenge for the 
receive.. you'd need two inputs with different resistors.


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Re: [time-nuts] IRIG B

[jimlux]

Hal Murray wrote:

The IRIG-B decoder work I did was implemented on power systems relays &
disturbance recorders several years ago, then I left the company and in the
meantime, they changed over to an FPGA implementation and skipped the
processor altogether.  Now I'm back with that same company (although
ownership has changed), but I haven't yet had a chat with the new FPGA
designer to find out how he did it :-)


Interesting.  I'd like to know why they switched to FPGA.

I thought the consensus in the FPGA world was that if you could do it in 
software that was probably the better way to go.  The main idea is that it's 
easier to hire programmers than FPGA designers.


I'd expect silicon costs to be roughly equal.  In a FPGA you are "wasting" a 
lot of silicon for routing.  In a CPU, you are wasting it on instruction 
decoding.  Both are high volume parts riding the crest of Moore's Law.  Of 
course, algorithm details may push you one way or the other.





Maybe you have an all FPGA design otherwise, and just want to add IRIG 
to it?


Maybe you've got both FPGA and CPU resources in the box, and the CPU is 
used for non-real-time-critical stuff, and you want to do timing in 
hardware (that's my situation).


Not all applications are high volume.. even a mid volume app might need 
enough glue that one FPGA is a better choice than a uC and a FPGA.



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Re: [time-nuts] IRIG B

[jimlux]

Magnus Danielson wrote:

On 05/26/2010 01:09 AM, Bob Camp wrote:

Hi

Like all the rest of us I'm making assumptions. I *assume* that we're 
talking about an implementation that will handle IRIG over audio over 
a fairly wide dynamic range.


Well, like most cases, I'd assume it is over "sufficient" dynamic range. 
The signal itself doesn't require very high dynamics, 8 bit should work 
well, 12 bits should allow for less care in level settings, 24 bits is 
excessive but cheap and only real care is high amplitude/clipping.





if you've got a low speed ADC, (perhaps on the chip) that's one way to 
go.  You can also do stuff like use a output pin from the micro and some 
resistor/capacitor stuff to do a CVSD encoder, which you can pretty 
easily turn into the level data you need to decode the IRIG.


At some point, though, the Rs and Cs cost enough (in board space and 
installation cost, if nothing else) that you might as well get a ADC (or 
a bigger uC that has one on chip)..


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Re: [time-nuts] IRIG B

[jimlux]

Bob Camp wrote:

Hi

Strange as it seems, *stocking* the R's and C's can be an issue. There's also placement cost. Based on some of the numbers you see, the cross over point (IC to odd value R's and C's) is amazingly low. I'm not saying any of that's right, just that it's the way a lot of companies roll up the costs. 


Bob


Not surprising.. the cost to stock, pick, place, solder is probably the 
same for a small IC and a R or C.  So, the only possible saving would be 
 if the IC is a LOT more expensive than a single or two Rs or Cs.


There might be a power dissipation difference, or a temperature range 
difference that would push you one way or another.


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Re: [time-nuts] Most accurate small crystal

[jimlux]

Poul-Henning Kamp wrote:
In message , Jim 
Palfreyman writes:



I have timed the accuracy of this internal clock and have found it to be
pretty good so far. 17 days ago it was ticking over at 21.8 sec past the
minute and a quick visual inspection today and it was still *very* close to
that. I will confirm it properly tonight.


Being able to model the clock of each device precisely is a very important
part of the security of these devices.

The important part there, is that the clock runs at a constant rate,
but the exact value of the rate is not important, as long as the
bounds are known.




I don't know that it needs to be all that precise..

The way it works is that your fob steps through a list of (pseudo)random 
numbers, one per minute.  The server steps through the same list.  If 
you "call in" with a particular number, the server doesn't just check 
the current step on the list, it checks some (configurable) range of 
steps on either side.  If it gets a match, it resets the server's 
"current step" to the one that matched.


The approach is very similar to the "rolling code" used in garage door 
openers and wireless key entry systems for cars.


See patent 4,885,778.

I don't know if they actually try to model the clock rate.  I think if 
you get too many "misses" you just get another fob.


The thing steps at once per minute. Say you allow up to 1 minutes error, 
and that the XO has 10 ppm error (e.g. 1 second/day).. that's a minute 
every 2 months.




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Re: [time-nuts] Flood of low end priced VNAs on FleeBay

[jimlux]

Steve Rooke wrote:

Just noticed there is a flood of lower end priced (<$5k & <<$5k) VNAs
on FleeBay just in case anyone is looking for one. No need to thank
me, just buy me one as well :)

Steve



Interesting... be aware that a lot of those 8510s aren't the whole 
analyzer, just the display or RF section, without the source (sweeper). 
ANd not just any sweeper will do.. you need one that the 8510 can 
control over GPIB and that has the right sync in and out.


A full 8510 has 3 or 4 boxes (depending on whether it has the 
s-parameter test set).  And, they're getting mighty long in tooth and 
tricky to fix.  I've got a cranky one at work that locks up 
occasionally, and we've been trying to figure out why.


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Re: [time-nuts] Flood of low end priced VNAs on FleeBay

[jimlux]

Richard (Rick) Karlquist wrote:

We have a bunch of sweepers at work, and many of the them have
died and can't be fixed.  The only way they can be repaired is
to cannibalize one to fix another, assuming they don't have
the same bad module.  We have given away an 8510 to a school
and have others gathering dust.




that's what we've found..

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Re: [time-nuts] Flood of low end priced VNAs on FleeBay

[jimlux]

J. Forster wrote:

VNAs are very expensive toys. I have an HP 8753 and was just outbid on a 6
GHz source assembly.  :((

Mine has a very complex multi-chip RF Hybrid that has a partial failure,
so it only goes to 3 GHz. That's a serious problem with modern high-end
microwave gear, if anything dies, you're prettry much screwed.



Even something as old as an 8510 has the same problem.  It's not like 
you can get spare boards, assuming you can even figure which board is 
dead. Or, replace parts on the boards/modules.


OTOH, for <3GHz, less than a kilobuck buys you a pretty impressive PC 
peripheral style VNA.  Yeah, not the performance of a modern PNA, but 
probably better than sweeper/141T or even an 8510 class box in some cases.


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Re: [time-nuts] OT - HP 5183A Waveform Recorder - is it worth playing with?

[jimlux]

You can, of course, now get 12 bit digitizer PCI cards for your
PC.



Or heck, eval boards for 12 bit ADCs that have USB interfaces..

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Re: [time-nuts] A philosophy of science view on the tight pll discussion

[jimlux]

Magnus Danielson wrote:



Also, modern cheap programmable TCXOs break the model as they have a 
hump in the phase noise due to their locked PLL, which the original 
model does not allow for. The autocorrelation function will be quite 
different. Notice how this ripples over to other locked oscillators such 
as passive masers, GPSDO etc.





Yes.. once one moves beyond a simple oscillator/resonator and amplifier, 
you're out of the zone where the simple Leeson model will work all the 
time.  the curves have lumps and bumps, and simple approximations of 
integration don't work any more.



And then, you have the whole explaining "why do I care what the phase 
noise/Allan deviation is" or trying to relate noise performance to 
overall system performance.  (e.g. what happens if the phase noise at 
1MHz offset is 20 dB worse than expected?)


For some simple cases, blackboard sketches of reciprocal mixing and such 
help, but when it gets more complex... or when you're trying to relate 
an integrated phase jitter spec to the distribution that creates it




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Re: [time-nuts] DCF77 clock with UTC display 5

[jimlux]

Giuseppe Marullo wrote:
 >If it is, why not purchase an *analog* DCF77 synchronized clock, set 
it to local radio time and then just move the hands on the spindle to 
reflect UTC? That's what I did with my WWV clocks that only handle the 
US time zones. >Worked just fine.
Well, I could just buy a 3 USD LCD digital clock, set it to UTC and 
periodically realign for time drift, no worry about winter/summer time 
switch. How do you "handle" summer/winter time?


Either case, we could be hung, drawn and qartered for these tricks, 
wrong maling list.



Not necessarily.. time-nuttery could take many forms.

 What if you bought multiple clocks, and used them as an ensemble and 
collected statistics by hand (preferably on damp clay tablets, for 
better long term preservation)  Since the 3 dollar clocks probably don't 
turn-over to the new digit simultaneously, you'd have to decide how to 
take your data.


(sort of a Beowulf cluster of commodity clocks?)






I would probably have used a stamp2 with a DCF77 module, but I don't 
know how reliable could be the stamp2 as clock when the dcf77 signal is 
not present.


Probably I will need to resort to some special IC from Maxim/Dallas that 
would keep track of time, and the stamp2 should be used  to adjust the 
time.


Nice as a project, but I would rather prefer a ready made unit, after 
all I would just log correctly my QSOs.



For logging QSOs?  A sundial might work well enough..
(probably wouldn't work for EME sync though)




Giuseppe Marullo

I will have to ask in the ham radio world...

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Re: [time-nuts] TPLL secret reveled

[jimlux]

Ulrich Bangert wrote:







The next improvement to the old fashioned pure counter was the invention of
subclock interpolation schemes. A counter using this works so: After the
beginning of the gate time it waits of the next zero crossing and then
measures the time up to the last zero crossing within the gate time with a
fixed resolution of say 1 ns (like the well known Racal Dana
1992/1996/1998). The frequency value is then the result of a computation. If
you consider this working principle you notice that this is even more a
phase meter like thing than the original counter only thing. For that reason
frequency measurements with a counter like that are suited as well for ADEV
calculation.




I've always referred to these style counters as "reciprocal" counters.. 
(because the frequency is calculated as the reciprocal of the length of 
N periods of the input signal).  They've been around at least since the 
80s, especially for applications where you need short gate time, but 
measurement precision greater than 1/gate time. It was very popular for 
applications like intercept receivers in the signals intelligence area 
before straight digital processing (ADC and FFT) was practical.


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Re: [time-nuts] TPLL secret reveled

[jimlux]

Ulrich Bangert wrote:

Jim,

pardon if I correct you: The reciprocal counters were an intermediate thing
between the counting only and the subclock interpolating ones. A reciprocal
counter would notice when a frequency measurement would be too imprecise due
to an arkward relationship between that gate time and the frequency to be
measured.

With only a few zero crossings within the gate time a reciprocal counter
would use the frequency to be measured as the source for its gate time and
measure the frequency of its reference with that. The result is then back
computed to the frequency to be measured.

This principle has nothing to do with sub clock interpolation. Nevertheless
it is true that once that the reciprocal principle has been introduced it
has been used in all following technologies.

B


Oh...

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Re: [time-nuts] UTC and leap seconds

[jimlux]

Tom Van Baak wrote:


Whether the answer is (a) or (b) doesn't change the fact that
the earth day is a poor clock compared with other clocks now
available. Besides tidal friction effects which might be hard to
imagine, or lunar effects which you already know about, note
that every time it rains or glaciers form and melt it changes the
angular momentum of the poor spinning planet. Then again,
many OCXO are also affected by humidity...



The Chilean earthquake changed the angular rotation rate (or, probably 
more accurately, changed the direction of the axis of rotation as well) 
 of the earth a small amount, as do most large earthquakes.


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Re: [time-nuts] UTC and leap seconds

[jimlux]

Hal Murray wrote:

iov...@inwind.it said:

I was wondering, why we assume that  Earth's rotation is slowing down,
instead  that clocks are speeding up? 


The quick answer is that there is a mechanism that explains why the Earth is 
slowing down: tidal effects.  There is no corresponding way to explain why 
atomic clocks are speeding up.



How many different timekeeping mechanisms are there that are accurate enough 
to notice changes in the Earth's rotation?


Wikipedia says 2 ms/100 years and that it was noticed by Halley in 1695 and 
confirmed by Dunthorne in 1749.  I assume they were using the Earth's orbit 
around the sun as their reference clock.




how exactly would that work?  Are they measuring the number of "days" in 
a "year"?  How would one do that? See when the sun crosses in front of a 
specific star (to get the "day") (or an equivalent measurement at night 
of some sort)


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Re: [time-nuts] UTC and leap seconds

[jimlux]

Hal Murray wrote:

jim...@earthlink.net said:

The Chilean earthquake changed the angular rotation rate (or, probably  more
accurately, changed the direction of the axis of rotation as well) 
of the earth a small amount, as do most large earthquakes. 


Has anybody measured that?


I don't think you can measure it directly.. it's way smaller than lots 
of other effects


Is there a good URL on this?  (predictions if not data)  All I've found so 
far is a small NASA press release predicting 1.26 microseconds per day:

  http://www.nasa.gov/topics/earth/features/earth-20100301.html
(and a zillion news sources repeating it)


http://www.jpl.nasa.gov/news/news.cfm?release=2010-071&rn=news.xml&rst=2504


I remember reading something fairly detailed..it might have been on a 
newsgroup at work.I work at JPL, and Richard Gross is in a section with 
a lot of people I work with at JPL, so it might have been discussed at 
lunch.   I'll see if I can find out


You could probably send him an email and ask..
richard.gr...@jpl.nasa.gov

heck, he might be lurking on this very list..

Day length is one of his things
trs-new.jpl.nasa.gov/dspace/bitstream/2014/18309/1/99-1782.pdf
trs-new.jpl.nasa.gov/dspace/bitstream/2014/18398/1/99-1877.pdf
trs-new.jpl.nasa.gov/dspace/bitstream/2014/12097/1/02-0952.pdf


1 microsecond/day is 1 part in 1E11.

-


From a friend in radio astronomy (VLBI):


They had a lot of the right instruments in the right place.

  Graph of position (3 meters!):
http://ivsopar.obspm.fr/earth/tigo

  Description of the  TIGO package:
http://cddis.gsfc.nasa.gov/lw12/docs/Riepl_Tigo.pdf

  Letter from the director:
http://www.expres-eu.org/Chile_06032010.html





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Re: [time-nuts] UTC and leap seconds

[jimlux]

Magnus Danielson wrote:

On 06/12/2010 02:33 AM, Hal Murray wrote:


jim...@earthlink.net said:
The Chilean earthquake changed the angular rotation rate (or, 
probably  more

accurately, changed the direction of the axis of rotation as well)
of the earth a small amount, as do most large earthquakes.


Has anybody measured that?

Is there a good URL on this?  (predictions if not data)  All I've 
found so

far is a small NASA press release predicting 1.26 microseconds per day:
   http://www.nasa.gov/topics/earth/features/earth-20100301.html
(and a zillion news sources repeating it)

1 microsecond/day is 1 part in 1E11.


There is one place that keeps track of these things, the IERS. Their 
Bullentin B provides monthly reports of earth rotation observatoins.


The bulletin for relevant period of time is:
ftp://hpiers.obspm.fr/iers/bul/bulb_new/bulletinb.266
ftp://hpiers.obspm.fr/iers/bul/bulb_new/bulletinb.267

Explanations is in:
ftp://hpiers.obspm.fr/iers/bul/bulb_new/bulletinb.pdf

Clause 3 is of most interest, look at the OMEGA column (appended the 
bulletin b 267 data for a more complete time-series around the date of 
interest).


3 - EARTH ANGULAR VELOCITY : DAILY FINAL VALUES OF LOD, OMEGA AT 0hUTC

 LOD : Excess of the Length of day - 86400 s TAI
 OMEGA   : Earth angular velocity
 Description: ftp://hpiers.obspm.fr/iers/bul/bulb_new/bulletinb.pdf

DATEMJD LOD sigma  OMEGA   sigma
 (0 h UTC)  ms   msmas/ms  mas/ms

2010   2   2   55229  1.8681  0.0026  15.041066853460.045



 55287  1.3068  0.0018  15.041066951170.031


Yes, we see a dip there... but looking at the two-month data we se a 
regular pattern creating a dip there... and the lack of jump is 
interesting.


Essentially... I can't see it here.




And I think that's what I heard: it should have changed (permanently) 
but that it would be impossible to see without years of data to remove 
all the other effects.


My GPS friends (all in the same section as Richard Gross.. the same 
section are the folks who do precision measurements of gravity (GRACE 
and GRAIL missions), etc.) tell me that once you get down into a certain 
range of uncertainty (10cm=ish for GPS), there's a whole lot of factors 
that are all of about the same magnitude (tidal movement, atmospheric 
delays not due to ionosphere, ionospheric effects, continental drift, 
etc.)  So making absolute measurements requires lots of data and 
painstaking identification of each of the factors and removing it.


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Re: [time-nuts] UTC and leap seconds

[jimlux]

Magnus Danielson wrote:

On 06/12/2010 03:36 PM, jimlux wrote:



While it would be fun to know, the practical impact of such a change is 
very, very small, to the level of being ignored. Considering of a major 
event actually consisting of many hundreds of earth quakes spread over a 
rather longish period, it becomes more interesting to see how the 
aggregate behaves. But you also needs to understand what the effect was 
prior to the event as it built up. What is the effect over a 1000 year 
period (a short period in geological sense)? Consider the build-up of 
pressure and magma under a volcano, which progresses over many years 
before it finally accelerate. Gravimeters is routinely used to monitor 
this build-up. There are thus more sources to consider. Someone is 
probably studying that.




That's one of the things that missions like GRACE (earth) and GRAIL 
(moon) are designed to do.  They make very high precision measurements 
of the gravity field of the body around which they orbit. It's done by 
measuring the  distance between a pair of satellites  very, very 
precisely.  The measurement uses phase measurements on RF signals 
derived from high performance ovenized quartz oscillators (USOs).  Hence 
the relevance to timenuts... good clocks are used everywhere...


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Re: [time-nuts] UTC and leap seconds

[jimlux]

Hal Murray wrote:

[Chile quake]


   Graph of position (3 meters!):
 http://ivsopar.obspm.fr/earth/tigo



3 meters in one direction and 60 in another.


Just to make sure we are all on the right track, the scale on the graph is 
cm, so the motion was 300 cm West and 60 cm South.


I may have confused things by translating 300 cm to 3 m.  My head doesn't 
normally use cm but I can quickly grasp 3 meters.





That's not all that big a displacement for that size earthquake, 
although the location is a ways from the epicenter.

Here's a map:
http://www.gpsworld.com/government/mapping/news/map-chilean-earthquake-coseismic-displacement-derived-gps-data-9667


The local 1992 Landers quake (mag 7+) had a displacement of some 5-6 
meters horizontally and 2m vertically.  Imagine sitting in a car on a 2 
lane road, and 30 seconds later, the road in front of you is displaced 
the width of the road, so you're looking at no road.  This one has been 
studied a lot because there's a whole raft of precision geodetic 
measuring points near it, as well as experimental satellite 
interferometric SAR data, etc.




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Re: [time-nuts] Odd FTS 4060 Behavior

[jimlux]

Glenn Little WB4UIV wrote:

I do not know why the manufacturers insist on gold plating leads that 
are designed to be soldered.

Silver plating seems like a better solution.
In this case, it appears that pins were soldered that were not designed 
to be soldered.




gold does not tarnish, silver does



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Re: [time-nuts] Galvanic decoupling of GPS antenna

[jimlux]

Robert Benward wrote:

Yuri,
Another suggestion would be to look for a low power GPS; I can't image 
with all the GPSs out there in all those cell phones, that they all take 
40mA or more.  If you find one that does have low power, then locate it 
at the antenna and then you won't need an active antenna.  (canabalize a 
cell phone?)


Most cell phones do not have a full GPS receiver in them. They use 
various forms of assisted GPS to reduce the nanojoules/fix.



But what about putting a small solar panel next to your antenna. If the 
antenna can see GPS, the panel can see the sun (for the most part).  A 
cheap panel puts out somewhere around 50W/square meter, so that will 
give you a starting point. 100mW = 1/500th m^2 = 20 cm^2


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Re: [time-nuts] Galvanic decoupling of GPS antenna

[jimlux]

Robert Benward wrote:
I don't think the shield is rated for +/-250V, and I'm not sure I would 
want to handle RG-58 with 250V on the shield.If you do this, use 
triax cable and ground the outter shield, and make sure the breaker can 
interrupt the fault current (if the fault currrent is in the hundreds, 
or even tens of Amps then this would not be a good idea).


Bob



Sure it is.. It's almost certainly rated to 300V (most all wire is), and 
probably higher.  Recalling that RG-58 doesn't really describe a 
specific kind of cable or construction (especially these days.. what you 
get is "RG-58 type")


But looking at the data sheet for Belden 9310 (the first RG-58 that 
popped up on Belden's website), I see a max operating voltage of 1400V 
(and the 50V rating as well.. for UL uses, but that's a sort of bogus 
number, designed to fit in a particular regulatory category.. kind of 
like ICs with TID limits of 300kRad, the limit for non-export controlled 
datasheets)



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Re: [time-nuts] Galvanic decoupling of GPS antenna

[jimlux]

Robert Benward wrote:
Rated for 1400V from CENTER conductor to shield, not shield to the 
outside. If you choose to use RG-58 with 250V on the shield then you 
will need to put the entire cable inside conduit.  It is not acceptable 
to have any type of exposed mounting.


Bob



Yeah... I've been looking for the jacket rating...  As a practical 
matter, I've used solid dielectric RG-58 (both A and C flavors) to carry 
10kVrms AC (neon sign transformer type voltages).  Usually, you don't 
get breakdown between center/shield.


However, considering that ordinary PVC insulated hookup wire is rated at 
300V, I suspect it's ok.


Obviously, we're talking a transient here.. if you're floating the 
shield at 200V above surrounding objects/ground, a better solution is 
called for.



Interestingly, looking at MIL-C-17 (which covers coax)

There are several requirements for RG-58 (MIL-C-17-28)
Spark test: 5000V rms +10%/-0%
Voltage Withstanding: 5000Vrms +10%/-0%
Corona extinction voltage 1900Vrms minimum

Then, looking at the test procedures in Sec 4.8 of MIL-C-17G

Spark test (4.8.3) A test voltage at a frequency...shall be applied 
between the outermost braid or shield and the outer surface of the jacket.


Voltage withstanding (4.8.4) (a) For coaxial cables. The test voltage 
shall be applied between the inner and the outer conductor, with the 
outer conductor grounded.



Overall.. MIL-C-17 is a great reference on how to test coax (or to ask 
your coax supplier about how they test...)


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Re: [time-nuts] AVAR & Femtoseconds

[jimlux]

Robert Benward wrote:

Bob
Boy, you guys are really making me read a lot.  I'm digesting Wiki right 
now.


I see tau, but does identifying a tau of 1E-14 allow you to say you are 
locked to 10fs?  The smallest tau I've seen in my E1938 collection is 1E-1.


Bob
 


tau is the time over which the measurement is made, typically 1 second 
or greater.


loosely speaking, the 1e-14 is the average fractional deviation of 
frequency over that time period.


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Re: [time-nuts] EFC tracking

[jimlux]

J.D. Bakker wrote:

I wonder if anyone has done something like this before and could share
their experiences.


The general principle should work. However, as you're interested in slow 
changes, there are some error sources that might be unacceptable, 
including the drift of (differential) channel resistances for the 4066 
over temperature, voltage and time. As shown the scheme is also 
sensitive to impedance mismatch/drift on the two inputs. Charge 
injection is a bit on the high side on a 4066; a more expensive 
(A)DG4xx-series chip may improve on that.


Or the traditional chopper approach of a mercury wetted reed relay?
If you're processing with a sound card, you have the advantage that you 
don't need to process the samples coming from the time of transition 
(unlike a traditional analog chopper with synchronous detection), so a 
fairly crummy relay would probably work.  The key is that it can toggle 
at, say, 100Hz, forever.





I don't know if it qualifies as simple/cheap, but Analog Devices and 
others have single chip low-rate sigma/delta converters with good to 
excellent properties; these were meant for strain gauges but should be 
able to track slow-moving control voltages just fine. Interfacing them 
to a parallel port (or USB PP adapter) should be close to trivial. Do 
have a close look at the data sheet: some parts have unbuffered inputs, 
and present a fluctuating input impedance which might couple onto EFC 
lines. A simple isolation amp with one or two precision op-amps should 
fix that.



The eval board for the part may have a computer interface built into it.







JDB.
[had just been looking into this for a transistor matcher/noise test rig 
I'm working on]



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Re: [time-nuts] EFC tracking

[jimlux]

Steve Rooke wrote:


The eval board for the part may have a computer interface built into it.


So I need to locate this if possible, any pointer please?


Go to Analog Devices website (http://www.analog.com/) and find your 
ADC.. typically there's an eval board with a USB interface available. 
For an example, look at the AD7785.. it might not be what you're looking 
for, but it's an example of what's available.






Thanks for your help,
Steve







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Re: [time-nuts] EFC tracking

[jimlux]

Didier Juges wrote:

Steve,

You may want to check the "Analog Devices MiniKit for ADuC702x-series".

http://www.google.com/search?q=Analog+Devices+MiniKit+for+ADuC702x-series

This kit includes a 24 bit ADC and integrated ARM processor in a small PWB with 
all the tools and sample code to do what you want with very little code to 
write (you can probably use the sample code as-is).

The kit is $30 (or $35, depending on where you look...) and you will easily 
spend that much building something that will not work as well using your sound 
card.

Sound card ADCs are intended for audio, and I'll bet their linearity does not 
come close to that of the ADuC702x series, if you can even get the spec for it.




sound card ADCs, the high end 24 bit ones, are pretty darn linear, and 
have pretty good SNR as well.  120-130dB S/(N+Distortion+etc) wouldn't 
be unusual.


The surrounding circuitry is likely to be a bigger problem.  1 LSB on a 
1V p-p 24bit converter is about 60nV.


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Re: [time-nuts] EFC tracking

[jimlux]

Didier Juges wrote:

I can only guess at what a sound card with linearity specs
approaching those of the AD kit would cost, and it's still AC
coupled, and as Poul pointed out, has no long term stability spec.


This *is* an issue.. the audio ADCs have great performance in the "sub 1 
second" sort of regime.. small variations in gain or offset would have 
no impact on audio applications, but would be a problem with the EFC 
measurement..





To me, it sounds like a no brainer, pun intended :)

Alternately, my last HP3456A cost me about $50, and that's a 6 digit
DVM with decent specs. You will need an HPIB controller though, if
you do not already have one.



There is that...





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Re: [time-nuts] EFC tracking

[jimlux]

Didier Juges wrote:

I am not sure how to translate the IMD specs into integral or
differential non-linearity, but from what I have seen, IMD specs are
not significantly better for 24 bit sound cards than for the older
high-end 16 bit models, when high-end 16 bit models were available.
Noise specs are better, and that's about it.

In sound cards as in many other consumer products, customers equate
more bits to higher quality and today you cannot buy anything but 24
bit cards, regardless of the actual improvement obtained. I am not
sure the actual specs reflect the higher number of bits. I believe
Bruce has quite a bit of data on that.


Some of the high end ADC parts (not necessarily cards, which could 
greatly compromise the performance) are quite good... they're sold into 
applications for professional recording as well as the consumer gear.


The (amateur) software defined radio folks have looked into this, in 
connection with direct conversion type receivers, because it affects the 
performance on things like instantantaneous dynamic range: being able to 
 demodulate a small signal next to a big one, for instance.



So, over the, say, 100 Hz and up range, they're probably pretty good.






What I know is that the standalone A/D converters like the AD parts
referenced in the other emails have outstanding linearity specs (at
low bandwidth of course) at a price well below that of a "high
quality" sound card, so even if the specs were the same, it would
still make more sense to use the external device to measure a slow
moving DC voltage.



I agree there..



Didier


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Re: [time-nuts] Datum TS-2100 firmware updating

[jimlux]

erniepe...@aol.com wrote:

HI Julien,

Do you have a detailed info, docu about the TrueTime  XL-DC??

I have 2ea of this unit and one is not going to lock...
Any experience or help appreciated.

Rgds Ernie.


There's a fair amount of info on the XL-DC on the web. I assume your 
problem is that it's not getting GPS lock?  Is it getting ANY GPS data? 
 (it can take quite a while if it doesn't know where it is and has no 
almanac data)


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Re: [time-nuts] yet another GPSDO design, or so

[jimlux]

Bruce Griffiths wrote:

Attila Kinali wrote:

Moin,

On Sat, 26 Jun 2010 21:14:02 EDT
ewkeh...@aol.com wrote:

  
What you want is basically a Shera Board. That design has been around 
for

quite some time and has served me very well.
 

Yes. The Shera Board and similar designs serve as an example for me.

  

I have a total of six running
including two controlling Rubidium. There are in my opinion a couple of
problems: not every 4066 works on the design the 18 bit D/A is very 
hard to
find  and now expensive and the single step of the D/A is intended 
for a 1.7

E-13  frequency step.
 

Yes. My goal is to update the venerable 4066 with something more
modern and have components that are easy to get trough farnell, digikey,
mouser, and all the other distributors. Yes, 16bit D/A seems to
be the maximum that is currently available. It crossed my mind
to build a 24bit R-2R D/A using discrete components, but this might
have actually a worse performance than a off the shelf 16bit D/A.
(temperature drifft, resistor values missmatch, EMI, etc)


Attila Kinali
   
Its possible to build a 24 bit resolution D/A using a synchronously 
filtered PWM circuit.



or with a pair of current output DACs and a resistive divider/summer so 
you have a "high order" and "low order" voltage.



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Re: [time-nuts] yet another GPSDO design, or so

[jimlux]

Hal Murray wrote:

or with a pair of current output DACs and a resistive divider/summer so  you
have a "high order" and "low order" voltage. 


If it were that simple, the manufacturers would package it up into a single 
chip. :)


And they do... hence delta sigma designs..

Back in the good old days before big monolithic converters were 
available you cold buy a fast wide DAC that basically was a hybrid with 
2 smaller DACs and a prom that was burned at the factory.




I think there are two areas of interest.  One is the obvious one that steps 
on the high-order DAC won't cleanly map into a constant number of steps in 
the low-order DAC.


Yep.. but if  you're driving it from a CPU, memory is cheap...



The other is things like temperature shifts.  You have to work out the specs 
for both paths and take the worst one.



It certainly isn't easy..

But, if you need something that isn't readily available off the shelf 
(for one reason or another.. maybe you've got several thousand 8 bit 
DACs in your garage that you're dying to use... along with a well 
regulated power supply to run them all )






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Re: [time-nuts] Lightning strikes vs GPS antennas

[jimlux]

Michael Baker wrote:

Time-Nutters--

The 5-year Flash Density Map of the USA provided by
the National Weather Service indicates that my county
here in N. Central Florida experiences "16 and up"
strikes/sq-km/year.

< http://www.weather.gov/os/lightning/images/map.pdf >

Experience bears this out...

I live on 6 heavily wooded acres and have had at least
6 trees struck and killed somewhere on my property
over the last several years.

I make it a faithful practice to disconnect antennas
from any gear during the frequent thunderstorms we
experience.

I have considered fastening a GPS antenna on the end of
a 12 foot fiberglass pole and installing it in the top
of one of the trees next to my workshop building so that
it has a clear 360 deg sky view down to within a few
degrees of the horizon.

It would be nice to come up with some way to use fiber
optics to isolate the GPS antenna from the receiver.
Coming up with a solar panel and battery to isolate the
antenna and RF preamp power is no big deal but coming up
with a way to isolate the RF via fiber is more problematic.




I suspect what you're looking for is a *inexpensive* way to do this..

Fiber optic links for RF are an off the shelf thing.
Miteq or Ortel (among many others) have them..

You can also buy off the shelf fiber links optimized for GPS.

Typically, you send DC to the head end (or your solar panel/battery 
idea).. The actual receiver is on the ground.


Although, with inexpensive GPS receivers, you could put the receiver up 
there and just send the 1pps and serial data down the fiber.


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Re: [time-nuts] Nuts and Phoolery

[jimlux]

Steve Rooke wrote:

On 5 July 2010 06:10, J. Forster  wrote:

Why stop there? How about buying Russian Hydrogen MASERs and putting them
in hand-rubbed old growth teak boxes and selling them for $995,000?


They are pulling out 14,500 y/o kauri trees (hard wood) out of peat
bogs over here which are perfectly preserved in the lack of oxygen (I
have a cutting board made out of some). Maybe the boxes should be made
out of this wood because it has a zero oxygen content and was grown
before the advent of electricity and radio signals so none of these
are trapped inside it and will not interfere with the quality of the
audio. Also the very tight and narrow rings in the wood increase the
high frequency response and do not attenuate the reference frequency
of the HM leading to perfect sound. Combined with silver stranded litz
wire bunches rolled together on the thighs of virgin Cuban young woman
during a lunar eclipse to exclude the effects of solar flares.



Uhh.. solar eclipse.. you want the moon blocking the radiation from the 
sun, and, in reality, you probably want to wait a few minutes ( or 
hours) after the totality, because the particles move slower than light.


Of course, with a lunar eclipse, you have the earth blocking the 
radiation, but that happens every night, and I leave it to time nuts to 
determine precisely when the blocking effect is greatest (just saying 
midnight is probably only accurate to minutes.. what with equation of 
time and all)



Or some such foolery..


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Re: [time-nuts] GPS Common View

[jimlux]

Bob Camp wrote:

Hi

I just got through poking at a couple of TBolts with Lady Heather. It appears that you can indeed get the hardware and software to put the TBolt into single satellite mode. That may enable a pretty simple GPS common view setup. 

One way to do it: 

Somebody picks a set of sats and times that make sense. Since the constellation repeats it's going to be a fairly simple table of this sat / that time. 
At those times they run their TBolt against something pretty good and log the results

The logs get put on a site somewhere

Somebody else wants to do a comparison. They set up to monitor the same satellite at the same time. 
They log the data.

They download the posted data.
They run the math on the data, out comes a time comparison between the two locations. 

Should be fairly simple to try out. 


Anybody with a good house standard want to give it a try?



Couldn't you run your data against Gipsy/OASIS or similar
http://gipsy.jpl.nasa.gov/orms/index.html


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Re: [time-nuts] GPS Common View

[jimlux]

Bob Camp wrote:

Hi

From a quick look it's not real clear how you would go about extracting time from the software suite. It's certainly useful for navigation though. 


A secondary gotcha is that the TBolt likely has some internal "issues" that 
distort the data a bit. Running a TBolt on both ends should wash out the ones that are 
firmware based.

Bob





If you're intersted send an email to one of the guys who is involved 
with this.  I know that they do common-view time transfer, it just might 
not be with that package.  JPL has a bunch of groups doing this kind of 
stuff in the building between where I park my car and where my office is.


You might also try asking the folks at
http://igscb.jpl.nasa.gov/

For instance, they log raw observables of all kinds
http://igscb.jpl.nasa.gov/components/data.html
http://igscb.jpl.nasa.gov/components/prods.html

I'll ask around tomorrow, too.

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Re: [time-nuts] Loran-C Anthorn

[jimlux]

EB4APL wrote:
A word of caution here:  Don't trust Google maps coordinates for any 
technical / serious work, they can have errors in the 100´s meter 
class.   And also don't use the copyright date of the maps and images as 
a time reference, they normally are older than that. If you live in an 
area under urban development you can check what I mean.
Take in account that this is a beautiful thing for locating a restaurant 
or a route, and can be classified as a geomarketing tool, not a 
measuring one.



For that matter, what ellipsoid is google maps using?  GPS is WGS84, but 
many (if not all) topographic maps in the US are still NAD27 (the 
corrections are in the bottom left corner). The difference in horizontal 
position around where I live is some 30-40 meters.


Google has to reconcile their imagery, their map data, and their 
topography somehow, and I imagine they take it all to some common 
ellipsoid, but it's possible they don't.  (That is, nobody is using 
Google earth to fly a plane across oceans)


Especially if you are using digital elevation models (DEMs) (e.g. to do 
propagation path analysis), you can be off by 50-100 meters comparing 
the topography in the DEM to the feature on the ground.  A "3 second" 
DEM has horizontal control comparable to a 1:250,000 map.


If you see that phrase at the bottom of a USGS map "Meets national map 
accuracy standards" it helps to know that the standard is basically 
"positions are accurate to the diameter of a pencil point or about 
1/50th of an inch: 0.5 mm)"  0.5mm on a 1:250,000 map is 125 meters.



Google is my friend, and I turned up the following with respect to 
Google Earth (which is NOT the same as Google Maps, apparently)


"We represent the earth as a sphere (special case of an ellipsoid). The
surface of our sphere corresponds to 0 meters sea level. As far as the
KML coordinate system, we consider 0 meters altitude to be sea level,
and we draw KML and terrain in a way that's consistent with that.
Specifically, the EGM96 geoid is our sea level, a potato-like shape
that's smoothly varying but not perfectly smooth, and represents mean
sea level around the globe. The geoid (and therefore sea level) is
offset from the ideal WGS84 reference ellipsoid by as much as 200
meters or so in some places. "

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[time-nuts] rapid startup GPSDO

[jimlux]

Is there some (inexpensive) GPSDO that has a "time from power on in an 
unknown location to reasonably stable" in the <5 minute category?


Frequency accuracy in the 1E-9 range would be fine.

A regular old GPS has a Time to First Fix well under that, and it should 
be cranking out 1pps pulses with 1E-7 or 1E-8  precision pretty 
quickly.. Would it be fair to say that after 100 seconds, one could 
theoretically have driven that down another factor of 10?


As I understand it, a thunderbolt needs some number of hours after turn 
on to stabilize, but just how bad is it after, say, 5 minutes.


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Re: [time-nuts] rapid startup GPSDO

[jimlux]

Luis Cupido wrote:

Jim,

The implementation I've done on "reflock II"
(on a MAXII CPLD form Altera
http://www.qsl.net/ct1dmk/reflock.html )
Had fast aqs time in mind(*).
It captures in few 1pps pulses
and could stabilize to about 1% of dac range
in quite less then 60s.

How slower you need it to be in addition to the
above timings depends on how much you want to average
the 1pps. Having it fast it would obviously
track the 1pps jitter.

'how good you need' -> 'how slow it has to be'

These timings are off course after your GPS starts
producing good enough 1pps pulses.

Luis Cupido.
CT1DMK.

P.S. Super cheap approach is the reflockI
(on a $5 CPLD) for which I made also a 1pps code.
(but a few less specs and addons than II)

(*) uW Radio ham application where you arrive on the top
of the hill and switch all equipment on and can be making
contacts minutes after having better than 1e-8(1e-9).




that's precisely the sort of application I'm looking at..

Wheels stopped to on-the-air in <20 minutes.

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Re: [time-nuts] A different timenuts interest

[jimlux]

Morris Odell wrote:

Hi all,

I have been asked to help with the construction of a Foucault pendulum. This
is a long pendulum which oscillates in a slow stately fashion in a fixed
plane which appears to move as the earth rotates. In reality the surrounding
environment is really moving relative to the plane of oscillation.

The pendulum requires a sustaining system to compensate for the inevitable
energy loss with each swing. The system is located in the building and
therefore rotates relative to the pendulum. It needs to provide an impulse
which does not affect the plane of oscillation of the pendulum. I was
thinking of an electromagnet located below the centre of the swing which
would be pulsed appropriately as the bob passes over it.

Has anyone here had any experience with such a system of have any
suggestions regarding the sustaining system? This is an interesting and
challenging project.



Google should be your friend.  This is a pretty standard thing, and I 
recall seeing drawings of optical schemes with phototubes to detect when 
the wire passes through vertical (and triggering the pulse through the 
electromagnet below the bob).




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Re: [time-nuts] A different timenuts interest

[jimlux]

J. Forster wrote:

The problem is straight forward, except for sensing the position of the
pendulum so the impulse is applied at the correct phase.

There must be a bunch of published designs, but if I were to try it, I'd
use something optical or capacitive.

For optical, I'd put a annular ring of IR LED/Phototransistor assemblies
around the center, wired OR the outputs, and use the signal to trigger the
impulse. The bottom of the pendulum should be polished or mirrored.




The usual scheme is a couple of optical paths at the top of the pendulum 
with lenses to focus the beam down to a very small diameter (smaller 
than the wire diameter).  The two optical paths are at 90 degrees to 
each other, and are logically anded either by using a pair of 
detectors/paths, or by using a mirror to fold the path.


It's aligned with the pendulum perfectly stationary (i.e. it's been 
sitting still for a day or two) so the beam trigger occurs precisely at 
the center point.




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Re: [time-nuts] A different timenuts interest

[jimlux]

Eugen Leitl wrote:

On Wed, Jul 21, 2010 at 10:40:48PM -0400, Bob Bownes wrote:

Silly me, I just realized you need to compensate for the change in
length with temperature.


You could use an Invar wire.
 
Some insight from a friend (a proto-timenut) who was thinking about 
building a 1ppm free pendulum in air for a fancy grandfather clock.


Invar (aside from being expensive) isn't appropriate here, depending on 
the design. Its low CTE properties depend on not being mechanically 
stressed.


A better scheme is the traditional bimetal pendulum compensation 
approach of steel rod and brass bob that can slide along the rod. You 
pick the dimensions so that as the steel gets longer, the bob expands at 
a different rate (pushing the CG back up), so that the net movement in 
CG position is zero.  You change the relative diameters of the two metal 
parts to get the CTEs and movement to balance out.




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Re: [time-nuts] A different timenuts interest

[jimlux]

J. Forster wrote:

E  A Foucalt Pendulum is not about time! It's about motion in
inertial space.



are they not the same, underneath it all?

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Re: [time-nuts] Basic question regarding comparing two frequencies

[jimlux]

J. Forster wrote:

"..  more generic interface." ??

The vast majority of professional test equipment has GPIB. Virtually
anything else is an "also ran".

FWIW,

-John




these days, ethernet and USB are becoming more popular.  My own 
preference is Ethernet and I long for the day when I can ditch the last 
GPIB cable (and the stacking connectors where you always seem to need 
the one on the bottom of the stack)  Yes, GPIB provides some clever 
triggering across the interface, useful for things like sweepers and 
vector voltmeters, but I suspect that it's not much used these days.. 
rather you wind up sending binary or ascii strings across the interface.


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Re: [time-nuts] Basic question regarding comparing two frequencies

[jimlux]

J. Forster wrote:

I very much doubt that the majority on this list have major govenmental or
corporate funding and shop from the new Agilent catalog that just came in
the mail.

As a result, I'd guess almost all the commercial test gear in the
posession of listers is from 1970 to 2000. That says GPIB and almost
nothing else. A very few instruments did use dedicated ISA, LSI-11, or
RS-232, but the numbers are tiny.

The fact is that with GPIB you can cobble up a system to almost anything
from simple to complex very quickly.



But over the next few years, I suspect you'll see more and more of it 
coming onto the surplus market.  My fond hope is that my daughter will 
be able to capitalize on it.







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Re: [time-nuts] Basic question regarding comparing two frequencies

[jimlux]

J. Forster wrote:

Probably yes.

There are also a number of lower cost instruments (just above consumer
grade)like HF-VHF VNAs that implement much of the smarts in a PC on the
market.

As to high end instruments w/ USB or Ethernet, I'm not so sure. The USA is
doing less and less hardware development, so instruments are not being
bought in anything like the quantity as in the past.

A lot of the new Agilent and Tek gear (at all price points) seem to have 
Ethernet, especially if it has a LCD front panel. (there's that LXI 
interface thing, too)   Even power supplies.  Not much USB (at least for 
control.. these days, using a USB stick for data transfer seems 
ubiquitous.. they've replaced the floppy drive on scopes, etc.), except 
for RF power meters.. There's a whole raft of power meter heads that are 
USB, which makes sense.. the "hard part" is in the actual sensor, not in 
the meter which displays the power reading.


Mind you, because they do this by using single board PCs instead of the 
dedicated instrument controller inside, they're subject to all the ills 
of PCs (e.g. expectation of patch cycles, etc.)


It also seems that there's a more rapid turnover of equipment these days 
(probably because accounting rules allow 3 or 5 year depreciation) and 
so the idea of a place hanging onto a signal generator for 20 years is 
less common.  So that newer gear will show up used sooner (I hope!)



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Re: [time-nuts] Basic question regarding comparing two frequencies

[jimlux]

Hal Murray wrote:

jim...@earthlink.net said:

But over the next few years, I suspect you'll see more and more of it
coming onto the surplus market.  My fond hope is that my daughter will  be
able to capitalize on it. 


A friend had a fancy scope with an Etherenet.  It got infected with the 
virus-de-jour.






Yes.. I was at a meeting at work last week where we discussed this. 
Seems it works like this: The equipment mfrs have about 6 month 
turnaround on patch cycles, so your instrument is almost always 
vulnerable.  But, if you don't connect it to anything or use it as a 
browser, you're ok.  Then, someone plugs a USB stick in (that is 
infected from some other PC).. and that infects the instrument.  SInce 
the instrument isn't running anti virus (they're of limited value 
anyway, and usually have a performance impact that's unacceptable in 
embedded systems), the virus lurks there.  Then, when you DO connect to 
the network, it leaps into action, or, it infects the USB stick of the 
next poor schlub to use it.




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Re: [time-nuts] Basic question regarding comparing two frequencies

[jimlux]

Steve Rooke wrote:

That seems to indicate these devices are running a version of embedded
Windows for them to get infected by a virus and I wonder why they need
such a sledgehammer internally.

Steve
PS. sorry for top-posting but that's the only way I can reply at the
moment (basic HTML Gmail).




Yes.. most are running some flavor of Windows Embedded (formerly known 
as WinCE) or WinXP.  It's a cost driven thing.. small form factor 
motherboards are readily available, windows gives you a familiar (to 
most users) interface for doing things like setup of the network 
interface, file system, etc.  I'd say it's probably cheaper (in a 
capital investment sense) to put a small PC into the instrument than to 
design your own custom controller board, write embedded software for it, 
etc.)


Especially if you want commonality across your whole line, where the 
higher end instruments have fairly sophisticated add-on software (all 
those slick applications that analyze signals, set things up), choosing 
some sort of popular OS platform makes sense.


MS makes it pretty easy to do the development.. The Visual Studio 
products are inexpensive, well integrated, etc. They've got decent 
documentation for generating stripped down installs suitable for 
instruments.  They also have update management, etc.


Some flavor of Linux is really the alternative, and the learning curve 
to get started with embedded applications is a bit steeper, especially 
if you want more than what can be done by a command line interface. 
Which GUI toolkit do you use? Where do you get it? etc.   With Windows, 
that whole list of choices has been made for you.



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[time-nuts] Test gear with embedded PCs Re: Basic

[jimlux]

David C. Partridge wrote:

Jim,

It might appear on the 2nd user market sooner, but the odds are you
won't be able to either repair it or calibrate it as the manufacturer
will have been the only supplier of either of these services, and no
service manuals will exist.


But is this any different than existing test equipment? I agree that 
there will be some weird widget interface between the embedded PC and 
the hardware, and that might be challenging to reverse engineer and 
duplicate, but overall, I don't know that it's any different than doing 
it for 20 year old gear.


Different processes, but fundamentally the same kind of problem.

What would be a bigger problem is availability of device drivers and 
such, especially if the OS has some sort of inherent life limit built 
into it (e.g. a digital rights management feature like Windows Genuine 
Advantage.. can't connect to the server, and your scope stops working)


For the intended original market, having to connect to a server every 6 
months or year when it's in for cal isn't a big deal.  However, in the 
recycled market, 10 years later,






If it is still in support, the mfr will calibrate/fix it for you if
your pockets are deep enough (probably as much or more than you pay
for it).  If (as is likely), it is out of support, then it will only
be good for re-cycling or land-fill :-(


Yes..




H does anyone but us old fogies see anything wrong with a
business model where stuff can't be fixed and has a support lifetime
of 5 years or so ?



I don't know that it's "can't be fixed" any more than any other old test 
equipment.  There's plenty of HP gear out there that has parts that 
cannot be obtained any more, and folks who are motivated find 
substitutes, etc.


It's certainly "uneconomic" to fix, in the sense that for someone who's 
using the equipment in their business, there comes a point where it's 
cheaper to buy/lease new gear rather than fix the old stuff. And, an 
equipment mfr can make a legitimate decision to not design for infinite 
repair life in exchange for lower original sales price.  Yes, this sort 
of shafts the hobby/tinkerer market, but it's the economic world we live in.


And not only the hobby market gets the problem.  At JPL we've got 
bunches of 8663 signal generators that are decades old, and for which 
there's no equivalent modern replacement that has all the "features" of 
the 8663.  (that is, the new E8663 doesn't work anything like the old 
8663 in terms of sweep behavior, phase modulation, or reference input 
handling)


But, because those 8663s were real workhorses, and because we have 
enough hangar queens to scavenge parts from, we kept them going for 
long, long after their intended life span, and never invested in finding 
a suitable new replacement (or, more properly, finding a new replacement 
and working around its idiosyncracies, like we did with the 8663).  Had 
we had a regular "replace every N years" strategy (where N is 5 or 7 or 
??) we wouldn't be lulled into complacency.


(note that a given space mission has a lifetime from "buy equipment" to 
"end of mission" on the order of 7-8 years.. for something like Cassini, 
it takes 7 years just to get to Saturn, after 3-4 years of development 
of the hardware)


It's really a "test setup design philosophy issue".. how much do you 
depend on idiosyncracies? Or can you design for a generic widget.


Even if you're working in the consumption of surplus, if you can "design 
for the generic widget", then you shouldn't care that there's a planned 
obsolescence thing going on.  IN theory, all that obsolescence should 
result in more surplus gear on the market at lower prices.


(assuming that the surplus market evolves...)



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Re: [time-nuts] Regulating a pendulum clock

[jimlux]

Bob Holmstrom wrote:

Food for thought.

I find it interesting that no one has suggested alternatives to 
improving the performance of a pendulum clock other than controlling it 
with a higher performance clock.  If the goal is a better clock why not 
attempt to understand the source of the errors and work on methods to 
control or compensate for them?  Teddy Hall has been taken to task for 
using a quartz controlled oscillator to measure the amplitude of a 
pendulum in the control loop of his Littlemore clock.


Tom Van Baak has developed techniques for analyzing the performance and 
hence potential error sources of pendulum clocks - perhaps he will share 
some of his work here.


Horological history is full of many attempts at solutions to the 
problem, but it would seem that the creativity of this group might 
generate some new ideas that are more in the spirit of better 
timekeeping than attaching the pendulum to a better oscillator.




Perhaps you really mean "better pendulum (or mechanical) timekeeping", 
because by pretty much any measure except aesthetics, vibrating rocks or 
atoms does a better job.


Mind you, I think that this is a worthy goal, because complex mechanisms 
that work well are a thing of beauty.



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Re: [time-nuts] Regulating a pendulum clock

[jimlux]

Bob Camp wrote:

Hi

For that matter, how hard is it to put it in a vacuum with temperature
control? Gets two big issues out of the way pretty fast. We certainly buy
crystal oscillators that are heated and enclosed in pressure tight
containers (not quite the same as vacuum, but close). 


Bob



temperature compensation to ppm accuracy is pretty easy, and has been 
done for 100 years or more.


Compensating for air drag changes with temperature might be trickier. 
however, the period doesn't change very much with drag.


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