Re: [time-nuts] WWVB remodulator for the Spectracom 8170...

[Charles P. Steinmetz]

Burt wrote:

In a sense you could say that Paul's circuit does get the WWVB 
signal to the receiver - it's just a new phase stable version of the 
signal signal.  This way I don't have to mess with the insides of the 8170.


Note that the 1 MHz TTL signal on the rear panel of the 8170 will not 
be phase locked to the WWVB carrier -- it will be phase-locked to the 
60 kHz carrier supplied by the re-modulator's crystal oscillator.


One might try to injection-lock the re-modulator's crystal oscillator 
to the WWVB carrier, but presumably the PSK would work against you here.


Best regards,

Charles




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Re: [time-nuts] PLL Dead Zone was Have 10 MHz need 19.2 MHz

[Charles P. Steinmetz]

Simon wrote:


The NXP 9046 is speced for zero dead zone.



"center frequency up to 17 MHz (typical) at VCC= 5.5 V"


Yes, that is what my message said:


The 74HCT9046 may be a better choice (no dead zone), but
you may need to select parts to run them at 19+ MHz.


Did you read it before replying?

Best regards,

Charles




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Re: [time-nuts] Have 10 MHz need 19.2 MHz

[Charles P. Steinmetz]

I received this all jumbled up in one long line without any sort of 
formatting, because the sender's mail client does not use 
standardized structure -- so I don't know who wrote what:



A 74HC4046 can reach 19.2 MHz


Be very careful about specs like that and be sure to read all the 
fine print.  What can run at that speed?  The VCO?  The phase 
comparator (and which one -- the one you want to use?)?  Also, note 
that the PC dead zone gets to be a larger and larger percentage of a 
cycle as the frequency increases, so the control gets less and less 
precise.  The 74HCT9046 may be a better choice (no dead zone), but 
you may need to select parts to run them at 19+ MHz.  No worries, 
there are hundreds of fast PLLs out there, but most are more 
complicated to apply than the 4046/9046.


Well some parts whose use is so pervasive, for example, the 2N3904 
and 2N3906 transistor, they will be around *forever* and reasonably 
priced.  I believe the MC or LM 1496 falls in this category.


Ten years ago I thought the same about the 2N, 2N2907, 2N5179, 
2N5109, 2N5320 and 5322, and on, and on, and on, and on  But they 
are all long gone as primary parts.  So will be the 1496 before 
long.  Of course, as long as 2N3904s are available, you can always 
build your own 1496 if you're willing to do a bit of selection.


BTW, I see that at least some versions of the ON 1496 are already EOL.

Best regards,

Charles




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Re: [time-nuts] Looking for an old french disertation

[Charles P. Steinmetz]

Attila wrote:

Hi, I'm looking for an old french diseration, 
which doesn't seem to be available 
electronically (at least i couldn't find it 
anywhere) and none of the libraries in 
switzerland seem to have it. Unfortunately, the 
author died a year ago, so i cannot contact him 
directly anymore. If anyone has an idea where 
and how i could get a copy (in any form) of 
Mécanismes non linéaires dans les résonateurs 
à quartz: théorie, expériences et 
applications métrologiques par Jean-Jacques 
Gagnepain, 1972 I would really appreciate your help.


The best place to start is usually the library of 
the institution at which the dissertation was 
presented.  If this was Mr. Gagnepain's PhD 
dissertation, his UFFC obituary indicates that he 
received his PhD from the University of Besançon in 1972.


His early papers may be derived from the 
dissertation, including "Non linear effects in 
piezoelectric quartz crystals" (Physical 
Acoustics vol XI pp 245-288, Academic press 1975).


John Vig listed many of Mr. Gagnepain's IEEE 
publications in an addendum to the UFFC obituary:


http://www.ieee-uffc.org/frequency-control/memoria-gagnepain.asp

Best regards,

Charles




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Re: [time-nuts] HP and other equipment failure

[Charles P. Steinmetz]

Luciano wrote:


About the HP5370 please got o see my solution


The fans would cool the transistors better if they were blowing on 
the heatsink fins, not directly at the transistors.


I use a slow fan that is large enough to blow over the whole heatsink 
assembly.  You can't hear it over the noise of the internal fan, and 
the transistors run at 35C.


Best regards,

Charles




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Re: [time-nuts] Spectracom 8170 Time of Day grief...(WWVB Clock)

[Charles P. Steinmetz]

Joe wrote:


In a slightly different direction, are there any commercially available 'PSK
Compliant Atomic Clocks' out there for those of us used to looking at the
'correct time'?

Also, what, exactly, was the advantage of changing modulation formats?  That
'killed' all the existing 'Atomic Clocks'?


No, it killed phase-locking instruments, including the Spectracom 
clocks.  Most "atomic clocks" designed for time-of-day use do not, 
and never did, phase lock to the WWVB carrier.  My 20-year-old 
Brookstone "atomic clock" still works just as it always did (within 
tens of mS AFAICT).  So should most other older "atomic clocks," and 
everything currently available from the many time-of-day "atomic 
clock" suppliers.


Best regards,

Charles




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Re: [time-nuts] Possible candidate for 10MHz sine distribution

[Charles P. Steinmetz]

Probably not a good choice for 10MHz distribution.  It's an NTSC 
composite video DA.  NTSC composite video is relatively low 
bandwidth, typicaly 5MHz or so.  Without complete specs in this DA, 
you can't rely on it having sufficient bandwidth, even for a 10MHz 
sine wave; certainly not sufficient for anything resembling a pulse 
or square wave.


Also, while the listing says the input and output impedances are 
"standard 50 ohms," the manufacturer's datasheet specifies 75 ohms 
(the NTSC standard):


www.megahz.com/specimages/Videotek/VDA-16-VDA-16A.pdf

It does not appear to have the headroom to handle a 1 Vrms (+13 dBm @ 
50 ohm) signal.


Best regards,

Charles




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Re: [time-nuts] Cheap 9.8Mhz Sa.22c's

[Charles P. Steinmetz]

David wrote:

I hadn't thought about the uA739 for a while.  It was one of the 
original low-noise amps - we used to use it for phono preamps.


If you could live with the anemic output drive, they were great 
opamps for the time.  I preferred the 749, which had an 
open-collector output (no 5k internal pull-down resistor).  I often 
used external current source pulldown, bias network, Schottky Baker 
clamps, and Class AB complementary emitter-follower outputs.  Once 
when 749s were unavailable but 739s were plentiful, a Fairchild 
engineer taught us how to open-circuit the 5k resistor cleanly to 
turn 739s into 749s.  The plastic DIPs were prone to 
sealing/passivation problems, so we always bought the ceramic parts 
(I pretty much always customized the compensation, so we couldn't use 
the 8-pin hermetic parts).


Re: glass piston caps, I have been able to sometimes get what I need 
from Surplus Sales of Nebraska


You can get ceramic piston trimmers from the usual primary 
sources.  For example:


http://www.spraguegoodman.com/pdfs/660.pdf
http://www.eyou.com.au/product/johanson-5202-rf-air-trimmer-capacitor-08pf-10pf-/
http://www.johansonmfg.com/pdf/Air-Capacitor.pdf

Eastern European clones show up regularly on ebay at much lower 
prices.  The ones I've bought have been made to high standards and work well.


I think glass piston trimmers are still available from primary 
sources, too, but I don't have a link handy.


Best regards,

Charles




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Re: [time-nuts] Cheap 9.8Mhz Sa.22c's

[Charles P. Steinmetz]

I think I have a acquaintance in USA that can maybe help but the 
shipping is going to kill me to death..


More so than buying a bunch of never-ending projects?

One question -- it seemed that you had gotten to a place where the 
(one of the?) 9390(s) seemed to be more or less working, but the Rb 
did not seem to be very well disciplined, at least at short to medium 
tau.  I know absolutely nothing about 9390s of any vintage, but it 
occurred to me to ask whether you're sure the GPS is used to 
discipline the Rb in a 9390.  Most of the telcom GPS/Rb units I've 
seen are GPS-disciplined OCXOs with an auxiliary RB that is NOT 
disciplined, but rather free-running, and used only for extended 
holdover periods.  Some of them correct for Rb frequency error to a 
first approximation -- for example, I believe the Symmetricom units 
with BesTime (e.g., TS-2500) monitor the Rb frequency as compared to 
the GPSDO during lock, then correct the output frequency during 
holdover (when the Rb is in use) by adjusting a DDS according to an 
estimate of the Rb frequency error -- all without actually disciplining the Rb.


Just a thought.  But, as I said, I have no knowledge of the 9390 so 
this is rank speculation.


Best regards,

Charles




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Re: [time-nuts] Traceability after loss of LORAN and WWVB

[Charles P. Steinmetz]

Jim wrote:

If I receive WWV, and measure it appropriately, can I say that my 
time, accurate to 1 second, is traceable to NIST, since they 
broadcast it quite accurately, and I can bound the uncertainty 
contribution from the propagation and electronics to less than a second.


That is, NIST certifies publicly that WWV is "on frequency" and "on 
time" with a certain precision.  Do I need to go to NIST and pay 
them to give ma piece of paper that says this, or can I use their 
published data?


If you are talking about legal traceability, you would need to follow 
all of the requirements of legal metrology.  The place where most 
"little guys" fall down with respect to traceability is demonstrating 
competence.


Typically, one would not get a piece of paper from NIST, although 
that is one potential way.  One would instead become accredited to 
the relevant ISO/IEC standard through a body other than NIST (thus 
certifying that your procedures are good enough to maintain 
traceability), then play by all the rules to keep the chain unbroken 
(most relevantly, making periodic measurements of WWV and comparing 
them to the published data).


Of course, the situation you posit -- time with an uncertainty less 
than 1 second -- is a very easy target, so demonstrating competence 
would seem (to an engineer) not to require accreditation.  However, 
as you noted in a later message, someone other than yourself needs to 
audit your procedures.  In the real world, this is done by 
accreditation.  In principle, I suppose you could have anyone you 
want audit your procedures, but the customers for your "accurate to 1 
second" time service might want someone they have heard of doing the 
auditing -- in which case, you're back to accreditation.


Best regards,

Charles




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Re: [time-nuts] Traceability after loss of LORAN and WWVB

[Charles P. Steinmetz]

Bob wrote:

At least the way I read the pdf's NIST seems to 
believe that GPS is legally traceable to NIST. 
It is the same "measure and then look up the 
data" sort of thing that LORAN used to 
be.  Took a while to read through them all…


Yes, that is correct.

Magnus wrote:


However, just taking time from GPS does not achieve NIST traceability.
   *   *   *
You can achieve NIST traceability (or to any 
other NIH) if you do a whole bunch of things 
_right_ and in accordance with relevant standards. Few do.


That is also correct.  Instruments are *not* 
"NIST traceable."  However, a measurement made 
with the equipment can be "NIST traceable" under 
certain conditions.  It is the PROCESS that 
produces traceability.  (I use "NIST" here for 
convenience -- any National Metrology Institute can be substituted.)


Sadly, you are also correct that few do the 
process right.  In my experience, about 80% of 
labs that claim they are calibrating 
frequency-measuring equipment to "NIST-traceable" 
standards really aren't.  (I've had this rather 
adversarial discussion with several dozen lab 
managers over the years.)  Of course, this does 
not mean their calibrations are not accurate, 
just that, from the standpoint of legal 
metrology, the instruments they calibrate cannot 
be used to make NIST-traceable measurements or 
perform NIST-traceable calibrations.  (When it 
comes to all of the "NIST calibrated" equipment 
you see on ebay, the figure approaches 100% very, very closely.)


The same is true the other way around.  You can 
have all of your equipment calibrated by a lab 
that works to NIST-traceable standards, but if 
you do not follow through with the traceability 
process the measurements you make with those 
instruments (including calibrations done using 
them) will not be NIST-traceable, from a legal metrology perspective.


Think of the traceability process as a 
chain.  One broken link and traceability vanishes.


One of the required criteria for traceability is 
*demonstrated competence*.  Generally, this is 
done by becoming accredited to the relevant 
ISO/IEC standard by an accreditation body.  No 
matter how sophisticated and meticulous someone 
is, if their lab is not accredited, they cannot 
make NIST traceable measurements or perform 
NIST-traceable calibrations.  Period.  This is 
where home labs and other "little guys" 
inevitably fail to preserve traceability.  Again, 
this does not mean that their measurements or 
calibrations are junk -- just that they are not 
NIST-traceable, as far as legal metrology is 
concerned.  The A2LA shows you what you need to 
do (see link in my last e-mail).


The OP may have thought he was making 
NIST-traceable measurements using WWVB and/or 
LORAN standards.  But if his lab was not 
accredited, that was not so.  Nothing has 
changed, in that regard, with the advent of 
GPSDOs (except that the uncertainty levels are better now).


Best regards,

Charles




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Re: [time-nuts] Traceability after loss of LORAN and WWVB

[Charles P. Steinmetz]

Scott wrote:


How are those of you dealing with traceability in the commercial space


The topic is known as "legal metrology."  Start here:



You need to click through lots of links to get the whole picture.  I 
believe the material is printed in the NIST Administrative Manual.


Other potentially helpful links:










Best regards,

Charles




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Re: [time-nuts] Follow-up question re: microcontroller families

[Charles P. Steinmetz]

I wanted to take this opportunity to thank everyone who has 
contributed so much wisdom on this and the other two microcontroller 
threads.  The last time I personally designed with uCs was 25+ years 
ago.  Much has changed, and you have given me lots to think about!


Of course, there was no unanimity in the suggestions, but everyone 
did a very nice job of telling it as they see it, without any 
religious fervor.  I also appreciate the in-depth discussion of 
development environments and operating systems, as well as hardware 
capabilities.


Ultimately, it seems likely that I will end up choosing two or three 
uCs to learn, maybe from the same family, maybe not.  It probably 
makes the most sense to start at the bottom, with an anticipatory eye 
toward which midrange uC I will take up next.  I expect it will be 
quite some time before I need a third part ("very fancy" uC).  At 
this point, I seem to be favoring parts with flash that support an 
RTOS, can be removed from the development board and installed into 
the system board, and have a good, low-cost development platform (so, 
I appear to have narrowed it down to only several thousand different parts...).


Again, thank you all for your comments.  I am still at the foothills 
of the learning curve, but I know much, much more than I did a week ago.


Finally, please do not take this message as a sign to abandon these 
threads, if there is more worthwhile to say.


Thanks again to all,

Charles







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[time-nuts] Follow-up question re: microcontroller families

[Charles P. Steinmetz]

On another thread, Bob wrote:

If the objective is to complete a very simple, low powered project 
and be done with it, go with the Arduino. If the objective is to 
learn an empire, be very careful about which empire you pick. The 
ARM boys are quickly gobbling up a lot of territory that once was 
populated by a number of competing CPU's. Learning this stuff, and 
getting good at it is a significant investment of time.


I'm starting a new thread because I don't want to hijack the first 
one, which I'm hoping will continue to provide useful information 
about the broad continuum of available devices, from the "easy enough 
for a child to assemble and program" to the "need to learn machine language."


My question here is more pointed: If one is going to learn a new 
system today for timing and other measurement/control projects, which 
"empire" is likely the best one to choose?


Of course, much depends on "what do you want to do with it?"  So, 
perhaps, the ultimate answer will be several families, each for a 
class of applications.  But on the other hand, some families may have 
a range of models that fulfill a wide range of applications.  Also, 
my personal approach does not require squeezing each project into the 
most minimal hardware possible -- as long as the added expense isn't 
huge, I'm fine with using more resources than necessary for smaller 
tasks if it means my investment in learning the system (and in 
programming tools) is leveraged more broadly.  Also, my personal 
needs generally do not run to battery or other low-power systems, so 
low power drain is not of great importance to me.


Some of the more systemic (less application-oriented) factors would 
be, which system is more versatile?  Which has the most useful PC 
cards (or development kits) available that do not require the user to 
start with a bare chip?  Which is likely to be around and supported 
longer?  Which is easier to program?  For which is one likely to find 
more programs to study and pirate, more libraries, etc.?  Which is 
easier to outfit with removable memory (USB drives, memory cards, 
etc.)?  Which has better and faster ADCs and DACs?  I'm sure there 
are lots of other factors worth considering, as well.


There may be good resources already available that address these 
issues.  If so, pointers would be appreciated.


Any books people recommend to get a feel for applying and programming 
these devices?


Much appreciated,

Charles







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Re: [time-nuts] Extron ADA 6 as 1/5/10 MHz DA

[Charles P. Steinmetz]

What I have been referring to as the "plain ADA 6" is properly known 
as the ADA 6 Component:




Judging from the dates on some of Extron's documents, it appears to 
be a newer model than the ADA 6 300 series -- which is consistent 
with Bruce's comment that his ADA 6 300MX had through-hole 
resistors.  Accordingly, it is possible that the ADA 6 300 models do 
not share the circuit I attached to my last e-mail.  As always, use 
due diligence!


Best regards,

Charles


Following the recent discussion of using the Extron ADA 6 as a 
distribution amplifier for 1/5/10 MHz reference signals, I dug out 
the schematic of the amplifiers and typed up my notes re: 
modifications (see attached).


Note that the ones I have are "plain" ADA 6's, not "MX" or 
"MX-HV."  I do not know if the MX or MX-HV units use this circuit 
or, if they do, if the component numbers are the same.  However, the 
gain-switching circuitry is present on the "plain" ADA 6 PC cards 
(but the switch itself is not), which leads me to believe that at 
least the MX version was built with this same card.


There may be other Extron video DAs that use this circuit -- in 
particular, models that have a PC card parallel to the rear panel 
and mounted to it by the BNC connectors may do so.


There is another, discrete design that Extron apparently produced at 
the same time, one example of which is the ADA 3 180.  This design 
cannot drive 50 ohm loads to +13dBm (1 Vrms) without severe 
distortion (negative peak clipping), so you need to attenuate the 
typical 1 Vrms input signal 6 dB to stay out of 
clipping.  Unfortunately, there is no easy way to modify this design 
to drive +13dBm into 50 ohms (and, IMO, there is a lot not to like 
about it for any use, including RGB video).  I have a schematic of 
that circuit, too, if anyone needs it.


Best regards,

Charles





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Re: [time-nuts] Distribution amps for Thunderbolt

[Charles P. Steinmetz]

Chris wrote:


I have been offered one of these:

ADA 6 300MX HV HDTV RGBHV 1 x 6 Analog Video Distribution Amplifier

I *THINK* it should meet my needs except the HV bit worries me. It
seems this means it has not got unity gain, but a gain of 0.7 or 1
volt, switch selectable. Could anyone comment if it's suitable to use
my Trimble Thunderbolt with several pieces of test gear at the same
time? Thanks. Here in the UK the ADA-3-80 seems a rare find.


"HV" just means that it has an additional sync channel ("Horizontal 
and Vertical").  I think "MX" means selectable gain.  I have two 
plain ADA 6's (no MX, no HV) that I used before I built my own 
iso/DAs.  The gain switching components are present, but the switch 
itself is not populated, so it runs at unity gain overall (the 
amplifier runs at x2 and each output is back-terminated).


My ADA 6's use 6, CLC409 amplifiers and, when modified with 50 ohm 
input and output terminations, each section (3 jacks) can drive 3, 50 
ohm outputs to +13dBm with ~1dB of headroom (I generally only fed 2, 
50 ohm loads from any one section).  Like any video DA, it should 
have much smaller coupling caps installed to restrict its 
low-frequency response to HF.


You need 21, size 1206 (SMD) 50 ohm resistors and some 100 nF 
capacitors to do the mod (I used NP0 ceramics).  You also need a deep 
socket (9/16", I think) to get the PC card dismounted from the back 
panel (it is mounted by the BNC connectors).


As supplied, there are 3, 1x6 DAs in the box.  You can parallel 
inputs internally as desired (deleting duplicate input terminations) 
to make one, 1x18 DA or one each 1x12 and 1x6 DAs.  You really 
shouldn't have more than one HF reference frequency running around 
inside a DA, so the 1x18 configuration is probably the most useful.


I was quite happy with mine for routine distribution of 1/5/10 MHz.

Best regards,

Charles




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Re: [time-nuts] Another David Partridge frequency divider question

[Charles P. Steinmetz]

Azelio wrote:


Usually the external reference input of measuring equipment is
internally squared, so if you feed a square or sine wave there should
be no difference.


Some external reference inputs may be DC coupled and zero-switching, 
in which case unipolar logic levels will not work well.  I don't know 
of any specific equipment to which this may apply, but if you try it 
and it doesn't work well it is one thing to consider.  An external 
coupling cap (or AC coupling the output internal to divider) should fix it.


Also, 74AC logic level (~ 5 Vpp) may be a little hot for some 
reference inputs.  Many reference inputs present a load impedance 
higher than 50 ohms to the source (often ~ 1k ohm), so you may not 
get the divide-by-2 attenuation from the open-circuit voltage that 
you expect in a matched system.  In this case, an external 50 ohm 
termination will reduce the level to ~ 2.5 Vpp.


Best regards,

Charles




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Re: [time-nuts] OCXO Adjustment Question

[Charles P. Steinmetz]

One further thought:  You say it drifts several Hz -- that seems like 
quite a lot, if you are making small adjustments.  I'd expect perhaps 
several tens of mHz at most, although if it was way off when you 
started, Hz might be possible at the first iteration.  I suspect you 
have a mechanical hysteresis and/or dirty contact problem on the 
adjustment cap or pot that you need to sort out.  If you can post 
details about the oscillator, someone here may have experience with 
that particular part and be able give you specific advice.  (You are 
positive it is an OCXO, not a TCXO?)


Best regards,

Charles




 Fred wrote:

I tried making small incremental adjustments but after I am done, 
the frequency drifts several Hz and then re-stabilizes at a new value.


That is to be expected.  Adjusting an oscillator is an iterative 
process.  After a while, you should get a feel for how far it drifts 
after adjustment, and whether or not the direction of drift depends 
on the direction you were turning the adjustment when you 
stopped.  In future iterations, you will stop adjusting about that 
far from the exact frequency and let the oscillator drift onto 
frequency (instead of adjusting for dead on and watching it drift away).


It would be good to get an educated guess (or information from the 
service documentation) about what you are turning (i.e., air 
variable capacitor, compression trimmer, or potentiometer setting 
bias on a varactor -- and if the latter, whether it is a multiturn 
or single-turn pot).  This information will help you understand how 
to cope with the inevitable mechanical backlash.  If it is a 
multiturn pot, you should always adjust, then back away just enough 
so that there is no further mechanical bias applied that might cause 
further motion of the wiper contact (i.e., put the adjustment screw 
in the middle of the backlash, biased neither one way or the 
other).  Also, if it is a potentiometer or air variable cap, the 
wiper (or capacitor rotor contact) may be dirty at the spot where 
you need to set it -- it is often helpful to exercise the pot or cap 
by running it significantly farther in both directions than you will 
need to go to set it on frequency, to try to clean the contact.


You should expect to see significant drift over a period of ten 
minutes to several hours, then slower drift for days to weeks until 
the crystal settles into its new frequency.  Every crystal is 
different -- some adjust right up with no fuss (a distinct minority, 
IME), some you chase for several months (again, a minority 
IME).  Note also that oscillators exhibit some sensitivity to 
gravitational orientation, so it is best to adjust it in the 
orientation in which it will be used (or else characterize its 
gravitational drift and set your target adjustment frequency 
accordingly).  Ovens aren't perfect, so if the ambient temperature 
around the oscillator is different when the instrument is buttoned 
up than it is when you are adjusting it, that can introduce another 
small shift.


How hard it is depends on the accuracy you expect and the resolution 
of your counter -- it is much easier to get it "spot on" (as far as 
you can tell) if you are using a seven digit counter than if you are 
using a twelve digit counter.


Best regards,

Charles






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Re: [time-nuts] OCXO Adjustment Question

[Charles P. Steinmetz]

Fred wrote:

I tried making small incremental adjustments but after I am done, 
the frequency drifts several Hz and then re-stabilizes at a new value.


That is to be expected.  Adjusting an oscillator is an iterative 
process.  After a while, you should get a feel for how far it drifts 
after adjustment, and whether or not the direction of drift depends 
on the direction you were turning the adjustment when you 
stopped.  In future iterations, you will stop adjusting about that 
far from the exact frequency and let the oscillator drift onto 
frequency (instead of adjusting for dead on and watching it drift away).


It would be good to get an educated guess (or information from the 
service documentation) about what you are turning (i.e., air variable 
capacitor, compression trimmer, or potentiometer setting bias on a 
varactor -- and if the latter, whether it is a multiturn or 
single-turn pot).  This information will help you understand how to 
cope with the inevitable mechanical backlash.  If it is a multiturn 
pot, you should always adjust, then back away just enough so that 
there is no further mechanical bias applied that might cause further 
motion of the wiper contact (i.e., put the adjustment screw in the 
middle of the backlash, biased neither one way or the other).  Also, 
if it is a potentiometer or air variable cap, the wiper (or capacitor 
rotor contact) may be dirty at the spot where you need to set it -- 
it is often helpful to exercise the pot or cap by running it 
significantly farther in both directions than you will need to go to 
set it on frequency, to try to clean the contact.


You should expect to see significant drift over a period of ten 
minutes to several hours, then slower drift for days to weeks until 
the crystal settles into its new frequency.  Every crystal is 
different -- some adjust right up with no fuss (a distinct minority, 
IME), some you chase for several months (again, a minority 
IME).  Note also that oscillators exhibit some sensitivity to 
gravitational orientation, so it is best to adjust it in the 
orientation in which it will be used (or else characterize its 
gravitational drift and set your target adjustment frequency 
accordingly).  Ovens aren't perfect, so if the ambient temperature 
around the oscillator is different when the instrument is buttoned up 
than it is when you are adjusting it, that can introduce another small shift.


How hard it is depends on the accuracy you expect and the resolution 
of your counter -- it is much easier to get it "spot on" (as far as 
you can tell) if you are using a seven digit counter than if you are 
using a twelve digit counter.


Best regards,

Charles




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Re: [time-nuts] Feldmann guide to the HP3586A/B/C

[Charles P. Steinmetz]

Brooke wrote:

There are a number of paragraphs with the same number and Appendix C 
is missing all the schematics.


The original was edited by a third party (including in particular the 
paragraph headers) around the time that Mr. Feldmann died.  I do not 
believe any important content is missing.  Appendix C indicates that 
the schematics (for several accessories to be used with the 3586) 
were posted to BAMA as two or three separate files (C1, C2, and C3 -- 
C1 and C2 may be in one file?), but I have not found them there.



PS both the links go to the same document.


Actually, one goes directly to the 2007/2008 v.2.1 PDF, the other 
goes to the BAMA HP3586 page where one can select that version or an 
earlier version (v.2.0, 2004), in case the direct link gave anyone 
trouble.  Note that there are paragraph numbering errors in both the 
earlier 2004 version and in the 2007/2008 edited version.  (I have 
not crosschecked to see if the paragraph numbering errors are exactly 
the same in the two documents.)


Best regards,

Charles








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Re: [time-nuts] Feldmann guide to the HP3586A/B/C

[Charles P. Steinmetz]

Gordon wrote:


Can you advise where one might obtain a copy of the Bill Feldman users guide
for the HP 3586B SLV?  I have one of these units and need all of the help I
can get.  Is it available as a PDF anywhere?


It is posted on the BAMA site:






Best regards,

Charles





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Re: [time-nuts] 10 MHz clock distribution for the lab

[Charles P. Steinmetz]

Russ wrote:

The HP 5334B has a 1k Ohm input impedance shunted by <20 pf it 
wouldn't hurt to terminate this input


This is pretty typical for reference inputs on test equipment.  The 
idea is that one 50 ohm source can feed a number of instruments using 
nothing but a series of Tee connectors, with the far end of the cable 
terminated in 50 ohms.  The 1k loads will cause little disturbance on 
the 50 ohm line.


If best isolation and delay matching are required, the source should 
feed a good DA and there should be equal-length runs of coax from the 
DA to each instrument, with proper terminations.  Generally, this is 
required only for measurement inputs -- it is rarely necessary for 
the references of different instruments to be phase coherent (and 
different instruments are likely to have quite different internal 
reference delays).


Best regards,

Charles




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Re: [time-nuts] Z3805A OCXO p/n 3505A09422?

[Charles P. Steinmetz]

Brooke wrote:


I'm trying to learn more about the HP Z3805A GPSDO.
http://www.prc68.com/I/Z3805A.html

It has an OCXO that I haven't seen before with a paper sticker with 
it's p/n: 3505A09422

The "A" normally means made in America.


Check the output on a spectrum analyzer for 5 MHz content.  I've seen 
several internet-sourced Z3805As that were explicitly claimed to have 
HP 10811-60165 oscillators, but actually contained unlabeled 
oscillators that look like this one and appear to be 5 MHz 
oscillators with doublers (the output contains 5 MHz at ~ -50 
dBc).  I have heard that Symmetricom may have made oscillators 
fitting this description, but have no further knowledge.


Best regards,

Charles






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Re: [time-nuts] Z3805A high value PU

[Charles P. Steinmetz]

Mark wrote:

For the first 6 hours PU stayed at 432us, then it dropped sharply to 
5.6us and then slowly climbed to 18us.

Doesn't seem right to me.


Nothing it does in the first 6 hours has anything to do with 
anything.  (1) The oscillator will be swinging around wildly 
(comparatively speaking, relative to its stability after it has been 
running unmolested for months).  (2) Further, 6 hours is almost 
certainly a shorter period than it normally uses to forecast PU, so a 
forecast after ANY six-hour period of data collection (even when 
fully warm and stable) will not be its best estimate.


I do not know HP's algorithm, but it sounds like it didn't seriously 
try to compute PU until after 6 hours, then it started trying with 
(1) too little data and (2) data from an unstable oscillator, so it's 
no surprise it is wandering around.  I'll be very surprised if it 
settles down near its long-term stability in less than a month of 
continuous, undisturbed running (continuous meaning don't turn it 
off, undisturbed meaning don't move it or bump it very hard -- if you 
do either of these, start counting from zero again).


Be patient.  OCXOs need time to reach stability when re-started in a 
new environment (particularly if they have been off for more than a 
few days and/or bumped around, both of which are probably true of 
yours).  Some are better about this than others, but what I've said 
is pretty typical of the 10811-and-better class of OCXOs, IME.


Best regards,

Charles






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Re: [time-nuts] Z3805A high value PU

[Charles P. Steinmetz]

Mark wrote:


I recently purchased a pair of Z3805A

The problem I am seeing on both is the predicted uncertainty is high 
compared to other receivers I have seen.


I am experiencing a PU of ~8us for the first and ~24us for the second.

My questions are,
What could be causing such bad figures?
Is it an oven problem?
Can I tweak it out?


The predicted uncertainty is calculated from the character of the 
OCXO drift over some period in the past.  If you just hooked these up 
after they were off for who knows how long and were then shipped, the 
OCXO will not even have begun to settle in.  I never really begin to 
think seriously about how stable an OCXO might be until it has been 
running continuously and undisturbed for several months.


There is every reason to think your units will settle in after being 
run continuously and undisturbed, but there is always the chance that 
they won't.  IMO, you won't be in a position to judge for several 
weeks, at the very least, more likely several months.


Best regards,

Charles








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Re: [time-nuts] SRS FS 730

[Charles P. Steinmetz]

Bruce wrote:


Switch mode power supply ?
FLL or PLL loop?


It's a distribution amplifier, so one wouldn't expect it to have an 
FLL or PLL loop -- and the manual does not mention one.  However, 
according to the manual it does have (in sequence) a low-Q LC input 
filter, a rather aggressive differential-pair limiter, and a high-Q 
filter (a 10.7 MHz IF transformer tuned down to 10 MHz).  The signal 
then goes through a 2.4x IC amplifier to seven output buffers, each 
comprising three emitter followers in series.  There is a low-pass 
filter (11.5 MHz) and a 20 MHz notch filter on each output.  [This 
all assumes that Magnus was using an Option 1, 10 MHz unit, which 
appears to be the case from his description of the circuit.]


Magnus -- I have a manual, but no schematics.  If you scan and post 
the schematics somewhere (e.g., Didier's site, 
), we will 
be in a better position to help.


Best regards,

Charles








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Re: [time-nuts] WWVB sync

[Charles P. Steinmetz]

Bob wrote:

Some of these clocks and watches seem to like midnight as the magic 
time to synchronize. That's certainly what the Casio's do.


Mine (it's a Brookstone, I don't know who manufactured it) will go a 
few days without a successful sync, then it switches to trying every 
two hours until it successfully synchronizes.  I think it will then 
use that time every day until you intervene manually or it has to do 
it again.  It also seems to adjust the local XO when it has daily 
success -- after running awhile with daily sync, it has outstanding 
holdover performance.


I'm in a low-signal area, but even here signal strength does not seem 
to be a problem.  Local interference at 60 kHz, however, is a big problem.


NIST Special Publication 960-14 (2009) gives recommended practices 
for WWVB-disciplined clock manufacturers and consumers.  (It may have 
been updated or replaced since the new modulation scheme was adopted) 



See this page for near-real-time signal monitoring 
status:  


Best regards,

Charles




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Re: [time-nuts] Lady Heather numbers

[Charles P. Steinmetz]

Peter wrote:


I am not convinced the temperature control in mine is functional.


Temperature control is a capability within Lady Heather (not the 
Tbolt itself) and requires external hardware (e.g., box and fan) to implement.


Best regards,

Charles




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Re: [time-nuts] Lady Heather numbers

[Charles P. Steinmetz]

Garren wrote:

Can anyone tell me how to turn off the satellite display on the 
lower right of the display?


In the "Graph" menu (type "g"), you have three choices for displaying 
the ADEV tables and/or the satellite map: ADEV tables only (type 
"a"), Map only (type "m"), or Both (type "b").  You are now in "Both" 
mode.  I don't know if typing "a" will go straight to the ADEV tables 
only, or if you have to toggle Both off (type "b") first.  But some 
combination of these will get you what you want.


Best regards,

Charles




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Re: [time-nuts] Lady Heather numbers

[Charles P. Steinmetz]

Peter wrote:

The antenna has a pretty clear sky view right now.  I have about 75 
feet of cable, 25 feet that came attached permanently to the 
antenna, might be RG-59, and a 50 foot extension which is a new 
piece of good quality RG-6 CATV cable.


Perhaps the antenna (came with the tbolt in the ebay deal) is not 
that good and I should get something better before taking the effort 
to get it up in its permanent location?


If you are not using a timing-grade antenna, changing it would be a 
good idea -- but be prepared for your c/n numbers not to change 
dramatically.  If you get a new one, make sure it is a 5 V antenna.


You say that the E and S exposures are pretty much clear, but the 
plot shows poor c/n below 30-45 degrees elevation.  You may find that 
your ADEV improves if you change the elevation filter to 30 degrees 
(it is at 10 degrees now), or change the signal strength filter to 
something >= 3.0 AMU (it is at 0.0 now; 3.5-4.0 is often 
recommended).  Either of these would reduce the number of satellites 
used by the Tbolt at any given time, but getting rid of the noisiest 
signals may improve overall performance as long as it does not cause 
the Tbolt to go into holdover for lack of satellites.


One of my Tbolts is in a location surrounded by tall trees and I have 
an indoor backup antenna in case the external antenna fails.  Using 
the backup antenna, its c/n plot looks not too different from 
yours.  After much experimentation, I found that the best performance 
with the backup antenna is achieved with the elevation filter set to 
30 degrees and the signal strength filter set to 3.0 AMU.


Best regards,

Charles






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Re: [time-nuts] Lady Heather numbers

[Charles P. Steinmetz]

Garren wrote:

I don't doubt that my oven could be the problem but I would think a 
lot of people have their tbolts sitting in a room or basement with a 
lot more temperature swing than 2.5C. I also monitor the inner oven 
temperature where the oscillator is located and it remains stable at 
67C regardless of the 2.5C swing of the outer oven. This makes me 
wonder if the tbolt temperature is used in the algorithm that steers 
the osc frequency. I'll have to try some experiments to see if I can 
figure this out.


What you see is the GPS discipline doing its job.

As others have said, the temperature reported by the Thunderbolt's 
internal sensor is not used by the Tbolt during locked operation (you 
can find lots of posts on this subject in the archives).  Note that 
your white oscillator trace sits stably on frequency (at time scales 
comparable to the temperature changes).  This is because the Tbolt 
control loop is counteracting the temperature drift of the crystal.


If the crystal frequency was not varying with temperature but the 
Tbolt was running the DAC up and down in response to the internal 
temperature sensor (as you posit), you would expect to see the white 
oscillator trace tracking the temperature and DAC traces as the 
oscillator was erroneously forced off frequency by the control loop.


Best regards,

Charles




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Re: [time-nuts] repairing General Technology (Tracor) 304-B rubidium standard

[Charles P. Steinmetz]

Could you put [scans of the manual] on a suitable server?


I don't know what server would be suitable.  *   *   *  Any suggestions?


http://www.ko4bb.com/Manuals/01%29_Upload_Instructions.php

Best regards,

Charles




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Re: [time-nuts] Low noise power supplies?

[Charles P. Steinmetz]

Joe wrote:

Back when I was in product engineering there was a VCO design that 
used a "superfilter" circuit. It consisted of a pass transistor and 
a filter cap from base to ground. The gain of the transistor 
multiplied the effective capacitance. I have not seen this configuration since.


They are often called "capacitance multipliers" and are popular with 
(among others) audio designers as low-noise supplies for low-level 
circuits (moving coil head amps, RIAA stages, etc.).  They are best 
used following an active regulator.  If the capacitor is 
electrolytic, it needs to be chosen very carefully so that leakage 
current noise doesn't spoil the effort.  Also, it is best to use a 
voltage divider on the base to give the transistor a bit of headroom 
(i.e., base voltage should be a volt or so lower than collector 
voltage, not the same as the collector voltage as happens when there 
is just a pull-up resistor on the base).


Best regards,

Charles






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Re: [time-nuts] Low noise power supplies?

[Charles P. Steinmetz]

Bob wrote:

An AD 797, a couple of metal film resistors, and a fairly large (say 
47 uf) plastic cap work pretty well.


The band from 10 Hz down to 0.1 or 0.01 Hz is generally important 
when testing oscillators.  To keep the 797 input noise density below 
a few nV per root Hz, the terminations must have very low 
resistance.  With such low resistance, a 47 uF cap won't even get you 
to 10 Hz, much less 0.1 or 0.01 Hz.


One more thought: Many oscillators have internal regulators that are 
not nearly as good as what you can build.  No sense using an external 
supply with 5 nV per root Hz noise density if it will be re-regulated 
inside the oscillator by a circuit that has a noise density of 250 nV 
per root Hz.


Best regards,

Charles




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Re: [time-nuts] Low noise power supplies?

[Charles P. Steinmetz]

tvb wrote:

I'll answer the question with anther question -- how does one 
properly measure power supply noise? Does it boil down to a single 
number, a couple of key numbers, or is it a plot, or several plots?


There are a number of "standard" ways, some of which have been 
mentioned by others, none of which is all that helpful IMO.


What I find most useful is a plot of noise density vs. frequency 
from, say, 0.1 Hz to as high as you require.  The data should be 
taken and processed with sufficient frequency resolution to show any 
spurs in the band of interest.  It is often helpful to have several 
plots, each covering part of the band of interest, to improve the 
displayed resolution of spurs.


NOTE:  Designing a preamp for collecting the data is far from 
trivial.  Articles have been written about it (see, for example, 
Linear Technology Application Note 124 by Jim Williams 
).


Best regards,

Charles




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Re: [time-nuts] Low noise power supplies?

[Charles P. Steinmetz]

Lester wrote:


For a regulated power supply, make one using a 723. The 723 has
far lower noise out than the monolithic regulators.


If you are willing to design your own regulator using a 723, you may 
as well use a few more parts to get a much better result.  Neither 
the internal reference nor the internal error amp in a 723 is 
anywhere near state of the art today with respect to noise, tempco, 
or speed.  Using readily available buried zener references and 
low-noise, high-speed op amps (or even a few discrete transistors), 
you can do several orders of magnitude better than a 723 in all 
respects.  The web is overflowing with designs (though not all of the 
circuits you find perform as advertised, so evaluate them with a 
critical eye and use your own sound judgment).


But wasn't the original question what is available off-the-shelf?

Best regards,

Charles




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Re: [time-nuts] OT, looking for a good science forum

[Charles P. Steinmetz]

Scott wrote:

Liquid acetone requires special handling and pressurized cells to 
keep it from explosively disassociating.


Did you mean "liquid acetylene"?  Liquid acetone is sold in nearly 
every hardware and drug store in the US, and is one of the usual 
solvents into which acetylene is dissolved in commercial acetylene 
tanks to render the acetylene safer.


Best regards,

Charles






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Re: [time-nuts] "Better" gps antennas than a Symmetricom 58532A

[Charles P. Steinmetz]

Mark wrote:

Does anyone have any suggestions for an antenna that would be 
significantly better than a Symmetricom 58532A for typical time nuts 
applications.   Immunity to other transmitters is also a 
consideration for me, and this may push me towards staying with the 58532A.


I use an AeroAntenna AT575-90 choke-ring antenna:

 http://ebookbrowse.com/at575-90-g-pdf-d359926216

They are available from time to time on ebay.

It is by far the best GPS antenna I have with respect to timing and 
position stability, presumably due to superior multipath 
rejection.  It also will work indoors where other antennas will 
not.  Regarding immunity from interference, it rejects the crud put 
out by my digiscope better than the others, but that is hardly a 
systematic test.


Best regards,

Charles




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Re: [time-nuts] Used Spectracom

[Charles P. Steinmetz]

Paul wrote:


Charles sort of depends on the signal quality.
My first approach shared used a modification to the 8163 to flip the phase.
But on the east coast things can be quite a challenge the squaring circuit
was unreliable.


I was responding to Joe's observation that you could use one of the 
Spectracom units as a phase comparator if you replaced the internal 
WWVB reference with an external reference.  The unit as modified no 
longer receives WWVB -- instead, you feed it 10 MHz from your GPSDO, 
cesium clock, H-maser, whatever.


Best regards,

Charles







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Re: [time-nuts] Used Spectracom

[Charles P. Steinmetz]

Joe wrote:

If [Spectracom WWVB receivers] were dirt cheap, I'd probably pick 
one up. If you could wire in an external standard, it would still be 
useful for the phase comparator.


That's what I did with my 8163.  You need to add a Wenzel-style 
two-PNP squarer and use the squarer output to replace the internal 10 
MHz VCO output (point "BB" on the 8163 schematic).  Removing the RF 
Amplifier PC card made plenty of room for the added board.  The 
existing two-PNP squarer on the Local input is marginal, so I 
modified it to conform to the one I added.  I disabled the VCO and 
the phase comparator that drives it by removing appropriate power 
supply feeds, and used the 60 kHz antenna connector for the 10 MHz 
reference input.  Extremely simple, and it works perfectly.


Best regards,

Charles







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Re: [time-nuts] Counter OCXO behaviour

[Charles P. Steinmetz]

Ed wrote:

Is it manually adjusted right at the oscillator? If so, just opening 
it up and sticking a screwdriver in there gives it a thermal shock, 
and the adjusted element will have mechanical stress that has to 
settle out too - the value can change for a while.


The 04E standard used in the military surplus 1992s (which are by far 
the most common 1992s in the US) is typically labeled "9462 454879, 
Rev. A".  There has been a fair bit of discussion on the list about 
these -- a search of the archive will turn up a number of threads.


Yes, they do tend to take a long while to settle after 
adjustment.  So long, in fact -- and with oscillatory gyrations above 
and below the starting frequency -- that I have speculated on-list 
that the adjustment may not be a direct adjustment of the tuned 
circuit (e.g., with the usual capacitor on the crystal), but rather 
an adjustment to the oven controller setting the crystal temperature.


Because the oscillators are sealed assemblies, I'm not aware of 
anyone who has taken one apart for analysis -- so the reason for this 
behavior must be considered unknown until we know what is going on inside.


Best regards,

Charles





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Re: [time-nuts] Need info on HP 1 MHz ovenized XO

[Charles P. Steinmetz]

Ed wrote:

On opening it up I found that the circuitry includes a 74LS73 dual 
JK FF, and a 74LS140 - very obscure - apparently a dual 4-input gate 
of some sort.


AFAIK, the '140 was only supplied in the "S" series (74S140).  It's a 
dual 4-input NAND 50 ohm line driver.


Best regards,

Charles







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Re: [time-nuts] PRS10 schematic or part identification help

[Charles P. Steinmetz]

Nate wrote:

The PRS10 manual has a full parts list and makes numerous references 
to the schematic, but the schematic itself isn't part of the 
document. Anyone able to confirm the identity of the part I'm looking at here?


For schematics, see .  Search for "prs10".

I see Corby has confirmed that it is C900.

Best regards,

Charles







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Re: [time-nuts] Thunderbolt oven / non-stable operating temperature

[Charles P. Steinmetz]

tvb wrote:

the tempco can be inferred from temp and quadratic PPS offset 
residuals (EFC gain is not a factor in this case)


It would be interesting (to me, at least) to know the spread of EFC 
gains from a reasonable population of Tbolts.


Best regards,

Charles









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Re: [time-nuts] Thunderbolt oven / non-stable operating temperature

[Charles P. Steinmetz]

Sarah wrote:


> All three have Trimble 37265 OCXOs

Just a curiosity. Is there any way to check that via software? Did you
just physically look under the cover, or how did you figure out which
type of oscillator your thunderbolt has?


You need to open it up.  There is a sticker on the OXCO can:

Emacs!



Best regards,

Charles






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Re: [time-nuts] Thunderbolt oven / non-stable operating temperature

[Charles P. Steinmetz]

tvb wrote:


do either of you have actual tempco numbers?


I checked my notes and found that I did not record any free-running 
tempco values.  My observations were based on the scale factors I had 
to use to get the temperature and DAC graphs in Lady Heather to 
overlay each other.  I initially noticed it because there was a very 
pronounced tracking of the two graphs for one Tbolt and for the other 
two there was not (the temperature-compensating component of the DAC 
voltage is mostly lost in the noise).  I had checked the actual EFC 
sensitivity of each oscillator in the vicinity of the operating 
point, so all relevant variables were more or less controlled.


My impression is that the better ones are comparable to a single-oven 
10811, maybe even a bit better.  LH typically reports tempcos of 
1e-12/C to 1e-11/C.  My worse unit (and, from what I can infer from 
LH plots posted to the list and on-line, it appears many others as 
well) typically reports a tempco of 1e-10/C to 1e-9/C.  Of course, 
the LH numbers are all to be taken with some caution since LH does 
not have any a priori means to separate tempco and drift.


Best regards,

Charles









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Re: [time-nuts] Thunderbolt oven / non-stable operating temperature

[Charles P. Steinmetz]

Mark wrote:

Although the Trimble oscillator has superb phase noise 
performance,  it has TERRIBLE temperature sensitivity.


It appears that most do but some don't.  Between the results I have 
seen posted on the list (Lady Heather screen shots) and my own data, 
they seem to fall into two groups.  I have two with excellent 
oscillator tempcos, but a third unit I have is about 100x worse and 
the sign of its tempco is reversed compared to the first two.  That 
one appears to consume approximately the same oven power as the other 
two, and heats the housing approximately equally, so the oven does 
not appear to have a gross failure.  All three have Trimble 37265 OCXOs.


I initially thought the third unit's oven controller was broken (low 
gain).  Then I noticed that the great majority of posted Lady Heather 
plots appear to be from units similar to that one, with the much 
higher tempco and reversed tempco sign compared to my two low-tempco 
units.  But I have seen a few other plots that appear to be from 
units similar to my first two.  The two with the low tempcos do not 
appear to be inferior to other Tbolts with respect to stability, PN, or aging.


I'm inclined to think that all 37265 OCXOs are supposed to work like 
my first two, and that the ones with large tempcos are the result of 
a supply or manufacturing error (most likely, a mismatch between the 
oven set point and the crystal).  But who knows?  There do seem to be 
many more of the ones with large tempcos around.  It would be 
interesting to take a few 37265s apart to see if there are any 
obvious differences between the high- and low-tempco units, and if 
tweaking the oven set points would reduce the tempcos of the high-tempco units.


Best regards,

Charles









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Re: [time-nuts] Thunderbolt oven / non-stable operating temperature

[Charles P. Steinmetz]

Warren wrote:

During normal operation my Tbolt uses the temperature and ADC data 
to in its Kalman filter that then can predict a simple linear 
temperature constant, and simple linear ageing rate.

   *   *   *
But the **Only** time the Kalman filter is used is during 
Holdover.  It does this by adjusting the EFC voltage in small steps 
making a simple linear ramp as a function of time, Plus a simple 
linear output as function of delta temperature.


I've also found that if the Temperature chip is the new one that 
gives only about 1 deg of resolution, All still works the same, But 
during hold over instead of seeing small continuous DAC changes as 
temperature changes, you see Big EFC steps.


That all sounds like the way it should work, if the temp sensor data 
is used internally by the Tbolt.


My notes indicate that I tried cooling and warming the isolated 
sensor during holdover and observed no effect.  However, the Kalman 
filter may not have been operating because I tested the unit 
immediately after it reached basic stability, before it had time to 
learn anything.



So what does this mean for the average Nut's Tbolt?   Mostly nothing.


I agree.  I presume that most time nuts would not ordinarily rely on 
a GPSDO during holdover -- particularly, a long holdover.


Charles










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Re: [time-nuts] Thunderbolt oven / non-stable operating temperature

[Charles P. Steinmetz]

Bill wrote:

Well, perhaps you are not looking close enough.  That is you need to 
be observing

at a finer level of comparison.  The changes, observed here and at another
location, are in parts in 10-10 to 10-11 range, sometimes 
larger.  At one of the

locations there was a direct correlation to the air conditioning cycle.


It is not clear what part of my message you are referring to.

My main point was that the information from the DS1620 temperature 
sensor does not appear to be used internally by the Tbolt.  In my 
observation, subjecting the sensor alone (thermally isolated from the 
rest of the Tbolt) to wide temperature swings (-10 to +120 C) did not 
produce any observabe effect on the operation of the Tbolt.  If the 
temp sensor data were used internally by the Tbolt, one would expect 
a significant effect from such a wide swing -- one that couldn't be 
missed.  If that large and fast a reported temperature swing produced 
effects only at the e-10 or 11 level, I would attribute it to 
imperfect thermal isolation of the Tbolt from the temperature 
stimulus (i.e., stimulus affecting the oven temperature or EFC 
circuitry of the Tbolt), not as the Tbolt's response to the 
temperature change reported by the DS1620 sensor.


If you were referring to my side point -- that allowing slow changes 
to the Tbolt housing temperature does not appear to be materially 
different from regulating the housing temperature -- my observations 
were that this was true down to at least 5e-13.  Of course, there are 
two variables -- total swing and rate of change.  By "slow," I mean a 
rate of change of 0.25C per hour or less [DS1620 reported 
temperature].  My diurnal swings are no more than 2C per day and 
usually less [DS1620 reported temperature] (they can be as much as 5 
or 6C seasonally, but those changes happen over weeks).  A/C cycling 
likely subjects the Tbolt to a significantly greater rate of change 
than what I mean by "slow," even if basic precautions are taken 
(e.g., putting it in a cardboard box).


Best regards,

Charles









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Re: [time-nuts] Thunderbolt oven / non-stable operating temperature

[Charles P. Steinmetz]

That temperature sensor does have an effect on the final outcome as 
it is part of

the internal equation.  So buffering the ambient temperature is important.


I've heard this before, but the evidence I have seen does not seem to 
support the proposition.


While switching the Dallas chip in one, I used the opportunity to 
bring the chip temporarily outside of the Tbolt housing on a cable to 
investigate whether the Tbolt makes any internal use of the 
temperature data.  Neither freeze spray nor bringing a soldering iron 
near the chip, when it was outside of the Tbolt housing and the Tbolt 
housing was well insulated from the changes in chip temperature, 
seemed to have any effect on the operation of the Tbolt, either 
normal or in holdover.


I have also run Tbolts with the newer ("wrong") temperature chips for 
long periods, and have not observed any systematic differences in 
performance between them and units with the older chips, either in 
normal operation or in holdover.  In Tbolts with the newer chips, the 
reported temperature often has little connection with the actual 
temperature and, at times, jumps abruptly, yet the Thunderbolts 
operate normally with no corresponding jumps in operating parameters.


My supposition/conclusion is that the temperature sensor was provided 
so telcom operators could get a rough idea of the temperature in 
remote cell-site transmitter shacks, not for internal use by the Tbolt.


As long as the Tbolt is housed so that its reported temperature does 
not change too rapidly, the oven control loop will keep the crystal 
very close to its set temperature over a wide range of ambient 
temperatures.  I have used this approach and have also actively 
controlled the housing temperature, and have not observed any 
material difference in frequency or timing stability between the two 
approaches.


Best regards,

Charles









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Re: [time-nuts] GPS DO Alternatives

[Charles P. Steinmetz]

Chris wrote:


The goal, well my goal is to build a GPSDO to this set of requirements

1) well under 1/2 the cost of the t-bolt.
2) can be made with common parts and skills most people have
3) is completely modifiable (open source software)

   *   *   *
if you could use the GPSDO a a local frequency standard for a 
counter that has 8 digits you are doing "well enough".  If you can 
get to 10 digital it is pretty good


OK, if we assume that a Thunderbolt is < $200 these days, the GPSDO 
module (no PS, no antenna) needs to be "well under" $100.  So, 
$75-80?  And to be clearly good enough for an 8-digit counter with 
one-digit overrange using gate times of 1 and 10 seconds, it should 
have an ADEV ~ 1e-10 at tau = 1 and 10 seconds.  Go down one power of 
ten for each digit over 8, and up one if the counter does not have overrange.


The performance at tau = 1 and 10 seconds will be largely dependent 
on the quartz oscillator used, assuming that its performance over the 
next two or three decades allows one to set the time constant of the 
discipline loop out in the 500 second range.


1e-10 is a bit more than one order of magnitude worse than an average 
Thunderbolt.  [1e-12 (what you would need for a 10-digit counter with 
one digit overrange) is somewhat better than you can expect from an 
average Thunderbolt.  1e-11 (what you would need for a 10-digit 
counter with no overrange, or a 9-digit counter with one digit 
overrange) is just about what an average Thunderbolt delivers.]


The holdover performance of the DIY box would likely not be as good 
as the Thunderbolt, because any sub-$100 implementation that can be 
made with common parts and the skills most people have is unlikely to 
include Kalman filtering or other predictive steering during holdover 
(but as I said in a previous message, holdover performance may not be 
required by many amateur time nuts, who can simply restrict their use 
of the standard to periods when it is performing nominally).


As we have discussed many times here, the control loop is much easier 
to design if it is comparing the 10 MHz output to a frequency much 
higher than 1 Hz.  This is why the original Miller DIY GPSDO 
(http://www.jrmiller.demon.co.uk/projects/ministd/frqstd0.htm) 
(http://www.jrmiller.demon.co.uk/projects/ministd/manual.pdf) is able 
to achieve such good results (comparable to an average Thunderbolt) 
with a very simple design -- it uses Jupiter GPS engines with a 
disciplined 10 kHz output.  I believe the PC card may still be 
available, for those who can find a Jupiter to use it with.  (Note 
that Mr. Miller also supplies a ready-made version of the GPSDO with 
Axtal OXCO, but that one costs well more than a Thunderbolt.)


The design goals stated above are ambitious, and I suspect it will be 
a challenge to come in on budget even with the relaxed stability 
requirement compared to a Thunderbolt.  But I do hope you give it a 
go, and will be most interested to see what you come up with.


Best regards,

Charles









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Re: [time-nuts] GPSDO Alternatives

[Charles P. Steinmetz]

John wrote:

What's *really* interesting, though, is the idea that collectively 
we might develop some standard measurement protocols that would be 
reproducible in a number of (amateur) labs.


I agree, but I didn't dare to dream so large when I wrote:


 From my perspective, the most interesting development would be an offer
by someone with a very well equipped lab to test any DIY GPSDO with a
consistent protocol and publish the results.  That way, we could all see
how the various approaches compare with respect to the characteristics
that are most important to each of us.


At bottom, any such testing requires (i) a comparison standard at 
least as good (and hopefully at least somewhat better) than the DUT 
at all taus and offsets (which may, in reality, be several standards, 
each doing part of that job), (ii) a reliable TIC (and, potentially 
usefully, frequency counter) that can exploit the stability of the 
comparison standard, and (iii) the capability to process the raw data 
to produce meaningful information.  [Additionally, to characterize 
poor-signal behavior one would presumably use attenuators and a 
well-situated antenna.  Some may not have good antenna sites to begin 
with, and in any case, it would be hard to standardize the signal 
strength between locations.]


My thoughts were (1) for many (most?) of the people who would want to 
build a DIY GPSDO, it would likely be their first "really good" 
standard, and therefore their best; and (2) the range of 
TICs/frequency counters owned by the target base is so wide, and 
covers such a large range of capabilities (to say nothing of whether 
any given counter is in good repair and being used to best 
advantage), that obtaining comparable results from one amateur lab to 
another would be just as much if not more dependent on the individual 
counters involved than on the GPSDOs under test.


However, that is no reason not to push forward with standardized 
measurement protocols, which would focus all of us on what the 
relevant desiderata are and how to measure them.


Best regards,

Charles








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Re: [time-nuts] GPSDO Alternatives

[Charles P. Steinmetz]

Don wrote:

you guys are reinforcing that just because its' cheap won't mean it 
won't work.


Of course it doesn't.  But keep in mind that "working" spans several 
orders of magnitude in this area, and what one needs to design and 
build depends on what degree of "working" one needs to support the 
uses to which the finished standard will be put.  First, there is 
performance during normal operation (good, continuous satellite 
tracking) -- ADEV at all taus of interest, PN at all offsets of 
interest, distortion and spurs, residual AM, stability over 
temperature, PPS jitter, etc.  Then, there is performance with poor 
satellite visibility, and finally performance in holdover (no 
satellite visibility) for however long one needs it (if one needs it 
at all, which many amateurs may not).  For some, there will be power 
consumption issues.  There may also be issues of interfacing to 
monitoring devices, both simple (e.g., LCD status displays) and 
sophisticated (e.g., computer running Lady Heather or Z38xx).  Does 
it need to work with existing programs, or is writing a new 
monitoring program part of the project?  Then there are the 
construction issues.  Does it need to be assembled entirely from 
connectorized modules, no soldering required?  Or capable of being 
thrown together on a scrap of perfboard?  Or will a PC card be 
designed?  If so, can it use SMT parts?  How adaptable must it be, 
particularly in accommodating different oscillators?  Does it need to 
support rubidium oscillators as well as quartz?  Etc., etc., etc.


Thunderbolt and Z38xx commercial GPSDOs are plentiful and relatively 
affordable, so they are natural benchmarks for any DIY project.


From my perspective, the most interesting development would be an 
offer by someone with a very well equipped lab to test any DIY GPSDO 
with a consistent protocol and publish the results.  That way, we 
could all see how the various approaches compare with respect to the 
characteristics that are most important to each of us.


Best regards,

Charles







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Re: [time-nuts] Considerations When Using The SR620

[Charles P. Steinmetz]

Paul wrote:

The following comment appeared on this list recently and it scared 
me a little:


Though the SR620 TIC is a great instrument when hunting the pico 
seconds we have to realize, that it's a thermal design desaster (I 
have to apologize to all sr620 friends). I have to run it for at 
least 12 hoursif not 24 to be shure, that every single part is at a 
more or less stationary thermal state. Some (NERC) say "...never 
switch it off".


I assume this instability is due to the instability of the internal 
frequency standard.  *  *  *  In fact, in our measurements, we plan 
to use a Cesium frequency standard as the timebase to our SR620. 
Does this anecdotal warning apply generally to the instrument or 
mainly to the use of the internal standard oscillator?


I concur with the comment above that the thermal design of the 620 
could have been better -- the sensing thermistor is in an "exhaust 
stack" between the fan (which is blowing out) and the rear enclosure 
wall.  This means that, instead of trying to maintain the internal 
instrument temerature at a constant level, it tries to maintain the 
exhaust stack temperature constant with a viciously fast response 
time that leads to instability at startup.  I have more than once 
considered moving the thermistor to a location near the TCXO, but 
since the fans always run up to full speed rather quickly at room 
temperature anyway, I have never bothered to try to improve the fan circuit.


Additionally. the TCXO remains powered during standby, but not 
exactly on frequency because the DAC that adjusts it during operation 
is not powered.  So, there is some settling from that adding to the 
temperature drift.  Note also that the DAC steps are not very fine, 
so you cannot expect to get the internal oscillator trimmed to better 
than e-9 or so.  SR apparently thought that most users would connect 
620s to external standards, so there was no reason to make them pay 
for a high-precision internal standard they would not use.


IME -- operating with an external reference that is better than the 
specified accuracy of the 620 -- they meet SR's specifications within 
a few minutes at most after switching on from room temperature 
storage.  (The trigger circuitry may drift a bit as it warms up, so 
you may want to check the trigger drift if your application involves 
slowish sine waves.  I have not investigated this.)  Ideally, you 
would let the instrument warm up for at least an hour and then 
perform an internal calibration before starting your measurements.


All that said, the only way you will know for sure how your 
particular instrument and standard will perform is to characterize 
them before you start your mobile measurements.  In doing so, you 
should observe a protocol that resembles the actual travel between 
measurements, at least with respect to time and temperature.  I 
strongly urge you to do this so you can have confidence in your measurements.


Best regards,

Charles







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Re: [time-nuts] GPSDO recovery from holdover

[Charles P. Steinmetz]

Hal wrote:


I can see two ways to recover.  One is to jump the 10 MHz clock by 10 cycles.
The other is to adjust the frequency so that the PPS slews back to on-time.

The first approach gives you a second with the wrong number of cycles.  The
second approach has your clock frequency off for a while with a trade off
between how far off and how long it's off.


Both the TBolt and HP38xx default to the second method you describe, 
and both can be manually forced to jump to the nearest cycle (TBolt = 
"jam sync," HP = ":SYNChronization:IMMediate"), which gets the PPS 
within 50 nS.  At that point, they revert to the first method and do 
the last <=50 nS by adjusting the oscillator frequency.


The TBolt allows you to program a "maximum frequency offset," which 
seems as if it should establish a limit on how fast it can correct 
the PPS, but I have never seen one come anywhere near the default 
maximum offset.  The TBolt also allows you to set a "jam sync 
threshold," which seems as if it ought to make the unit jam sync 
automatically when the threshold is exceeded -- but I've never seen 
one do that, either, even when set to "fast recovery."  So far as I 
have seen, jam sync only occurs manually.


Best regards,

Charles









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Re: [time-nuts] EIP545A 18GHz counter query

[Charles P. Steinmetz]

Chris wrote:


Band 2 should work from -20dbm (22mV RMS) right across its 10 MHz to 1
GHz range according to the manual. Even with 190 MHz into it it takes
at least 30mV to start triggering, sometimes up to 40 mV.  40 mV will
reliably fire it across its full range once it warms up a bit.

Band 1 specs are 22 mV from 10Hz to 1 GHz, and that band triggers with
just 15 mV at 10 MHz, but needs 25 mV at 100 MHz.

Band 3 specs are  12 mV at 1 GHz to 1.2 GHz (needs 15 mV @ 1GHz)


Ahh, I had missed that you were feeding the 10 MHz from the divider 
to the *measurement* inputs.  It sounds like a triggering issue.


Is the trigger coupling switchable from DC to AC, and is it 
adjustable for trigger level?


It is not unusual for the trigger point to drift a bit as a counter 
warms up, but at any temperature you should be able to find settings 
that will allow it to trigger on inputs at least close to the minimum 
the manufacturer specifies.  The figures you are seeing are not way 
out of bounds, especially if the trigger coupling and level have not 
been adjusted for optimum triggering.


Again, note that the divider output is unipolar (positive-only, does 
not cross 0V).  With a TTL input, you should get good, stable 
triggering with the trigger coupling set to DC and the trigger level 
set to ~+0.5V on the positive-going edge.  With sine-wave inputs, you 
may get best results with AC coupling and a trigger level at or near 
0V.  Look under "triggering" in the manual to see what the 
manufacturer recommends.


It's just like the triggering on an oscilloscope, if that helps -- 
what you would do to get a stable scope display is also what you need 
to do to get a stable frequency reading.


Best regards,

Charles







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Re: [time-nuts] EIP545A 18GHz counter query

[Charles P. Steinmetz]

Chris wrote:


I have the 10MHz output from David's divider feeding the counter. When
fed from this the Band 2 seems unreliable starting at 10MHz. If I feed
it 10Mhz at 50mV from my sig gen it starts reliably. Is it a mismatch
from the divider, or has it perhaps not got enough drive level?


First, what does the counter manufacturer's specification say with 
respect to acceptable signals at the external reference input?


Second, what happens if you feed the TB output directly to the 
counter's reference input?


IIRC, the outputs of the Partridge divider are 5V TTL from a ~50 ohm 
source, so low peak-to-peak signal amplitude should not be an 
issue.  If anything, the divider could be overdriving the counter's 
reference input.  Note that the TTL signal ranges from 0V to ~+5V and 
does not cross ground -- if the counter is expecting the reference to 
be bipolar (i.e., if it switches on a zero-cross), it may not respond 
reliably to TTL levels.


Beyond that, depending on how the counter terminates the external 
reference line, you may have steps or ringing at the reference input 
(see the thread on terminations).  Look at the counter's reference 
input with a high-impedance (divide by 10) scope probe to see what 
the feed looks like there.


Best regards,

Charles





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Re: [time-nuts] Z3805

[Charles P. Steinmetz]

Bob wrote:


I've heard much talk in this group about the power supplies on the Z3805.
*   *   *   my Z3805   *   *   *   started producing a real bad smell after a
few hours, the classic burnt transformer type.  *   *   *   I opened the
unit and found the 25W 5V, +/-15V (made by AT&T) was real, real hot.

 Is this the supply driving the heater inside the 10811?


There appear to be quite a number of different boxes available 
labeled "Z3805" these days, so information you get may or may not 
apply to the particular unit you have.  My Korean-made Z3805A takes 
nominally 24-27 V DC power and has a dual-oven 10811 OCXO.  I presume 
-- but do not know for sure -- that the ovens run from the raw DC 
supply, not from a DC-DC converter.


If the smell did come from the DC-DC converter block, it suggests a 
failure either in the converter itself or in the circuitry that is 
powered by the 15 V supplies.  I think the former would be more 
likely -- the converter should have internal protection that would 
step in before it got hot enough to smell, in case of a load fault.


A failed oven controller in the 10811 could also produce a burnt smell.

Whatever it was, it will very likely give a repeat performance at 
some inopportune time, unless you chase down the trouble first.  Not 
easy with an intermittent fault, but particularly if it was one of 
the 10811 ovens acting up, it would be nice to catch it before it 
happens again.


Hints:  (1) use your nose, up close.  Does one part have a residual 
smoky smell?  (2) Look very carefully, using a magnifier.  Does one 
part have ID markings that look faded or scorched, or small 
cracks?  Is anything leaking out of the DC-DC converter?  Also look 
carefully at resistors and polar capacitors.


Best regards,

Charles





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Re: [time-nuts] getting a grip on 10811 drift (trying to read my instruments)

[Charles P. Steinmetz]

Chris wrote:


According to the documentation I have, pins 2, 4, and 5 are all tied
together internally


I think you may be correct.  My recollection was that it needed to be 
done at the connector, but I may be mis-remembering.  Worth a check, though.


If you have Pin 6 ranging from + 5 V to - 5 V with respect to Pin 2 
and are only getting 50 mHz of frequency change, then yes, it appears 
that the EFC in that oscillator is not working normally.


Note that different versions of the 10811 have different nominal EFC 
slopes -- most are nominally 0.1 Hz/V (1 Hz/10 V), but some are 
nominally 0.25 Hz/V (2.5 Hz/10 V) (05071-60219, 05071-69219, 
10811-60158, 10811-60159, 10811-60160, 10811-60164).  The 10811 D/E 
Option 100 and Option H41 (10811-60125, 10811-60131, 10811E Option 
H41, 10811-60133, and 10811-69133) are "Not Specified" for EFC.  I do 
not know if this means they do not have EFC, or only that they are 
not guaranteed to meet any particular EFC slope.  I think the latter 
is more likely -- perhaps Rick knows and will comment, or someone 
here has an Option 100 or Option H41 oscillator and can measure it.


Best regards,

Charles









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Re: [time-nuts] getting a grip on 10811 drift (trying to read my instruments)

[Charles P. Steinmetz]

Chris wrote:


If I read this correctly, I'm looking at
9,999,999.97  Hz ?


Correct -- the small digit to the right is the exponent.  As others 
have mentioned, by holding the UP arrow key in for about 3 seconds, 
the 1992 will switch to a 10-second gate and give you one more digit 
of resolution, but you don't need that for this job.  BTW, the manual 
for the 1992 is pretty widely available on the web.



My EFC mapping looks like this (this was done before
I adjusted the coarse control)

-4.94 VDC 9,999,999.95
 * * *
 0 VDC  9,999,999.93
 * * *
+4.90 VDC   9,999,999.90


How and where are you measuring the EFC voltage?  Are you sure the 
voltage on the EFC pin of the 10811 (Pin 6) was the same as you 
measured?  Was the EFC return pin (Pin 5) connected to the oscillator 
supply return (Pin 4)?  If it is left floating, the EFC will not work properly.


Best regards,

Charles









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Re: [time-nuts] Z3805 hold-Over

[Charles P. Steinmetz]

Doug wrote:

I'll place a preamp in line to see if that increases the SS on the 
3805 , maybe my problem is the GPS RX isn't well. Great point.


Note that most GPS engines (including the one in the 3805) report 
carrier-to-noise ratio (C/N), NOT signal strength.  C/N is a function 
mostly of the antenna location (and, to a lesser extent, the antenna 
itself).  So, while a preamp will raise the signal strength, it will 
also raise the noise strength, and the C/N -- which is what matters 
-- will not change much.  The cure is to find a better location for 
your antenna (and possibly get a better antenna, but location is the 
main thing).  If the only better location you have requires a long 
cable run, a preamp may help to offset cable attenuation.


Best regards,

Charles





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Re: [time-nuts] getting a grip on 10811 drift (beginner-ish question)

[Charles P. Steinmetz]

Chris wrote:

My perpetually drifting 10811 pretty quickly made it to the negative 
voltage rail on the control voltage.


Is this an oscillator you just powered up after it had been off for a 
long time?  The most common versions of the 0811 are specified for 
drift of less than 5 x 10e-10 per day after they have been on for a 
month.  IME, they usually meet that spec within a week of being 
turned on, even if they have been off for a long time.  Mine run from 
about 2 e-11 to 2 e-10 per day (note that they are on continuously).


I put in a 1/4 watt 50 ohm resistor (like the parts list called 
for).  My working hypothesis is that the small resistor was changing 
impedance due to heat.


The 10811 output is specified as 0.6 Vrms max into 50 ohms, or 7.2 
mW.  I doubt that heating-induced resistance change was a significant 
problem.  But no harm changing it.


Best regards,

Charles





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Re: [time-nuts] Distribution amps and slew rate

[Charles P. Steinmetz]

david wrote:

Given that slew rate is so critical, why do we distribute sine waves 
and perform the zero-crossing detection at every target instrument?


Magnus made some good points in response to your question. To 
elaborate a bit: it is much easier to provide a friendly transmission 
environment for a sine wave (single frequency), and sine waves are 
less sensitive to imperfections in the transmission environment 
(impedance discontinuities and mismatches, noise ingress, 
etc.).  Reflections in the transmission environment will put funny 
steps in what started life as clean square waves or pulses, and 
differential phase shifts will also mis-shape square waves or 
pulses.  This can even be a problem with sine waves -- see, for 
example, the NIST paper on the timing effects of distortion in sine 
wave sources for an example of the sensitivity of sine wave systems 
to harmonics (Walls and Ascarrunz, The Effect of Harmonic Distortion 
on Phase Errors in Frequency Distribution and Synthesis) -- but it is 
much worse with square waves or pulses.


Sine wave systems are also much less prone to radiating 
noise.  Anyone who operates one or more frequency standards as well 
as sensitive RF receivers can testify that sine waves are much less 
of a hassle.


Best regards,

Charles





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[time-nuts] WWVB new modulation scheme monograph

[Charles P. Steinmetz]

This has probably already been posted more than once, but if anyone 
is still looking for a description of the new WWVB modulation scheme:


http://tf.boulder.nist.gov/general/pdf/2651.pdf  (Sept. 2012)

Best regards,

Charles




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Re: [time-nuts] documentation for beginners

[Charles P. Steinmetz]

I could start a Wiki for Time Nuts, if you like, or anyone else 
could start one of course.


Don't forget that Didier already has a wiki for precision timing:

http://www.ko4bb.com/dokuwiki/doku.php

Best regards,

Charles









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Re: [time-nuts] Hp 58503A

[Charles P. Steinmetz]

I  just loaded it down with a 50 ohm load and looks perfect.


One of my design pet peeves is not anticipating what users may 
do.  For example, not anticipating that someone might terminate an 
output in a high impedance rather than in the rated impedance, or 
leave unused outputs unterminated.  I have seen several multichannel 
isolation amplifiers where any output not terminated in 50 ohms is in 
hard clipping -- even with halfway decent isolation, this can put 
garbage on the other outputs.  The very definition of an isolation 
amplifier is that each output should be independent of how the other 
outputs are terminated -- short, open, inductor, capacitor, other 
signal, whatever.  I understand it is not trivial to provide 1 Vrms 
(+13 dBm) outputs with 6 dB overhead from a 5 V (or 3.3 V) supply, 
but that's why they pay designers the big bucks.



Best regards,

Charles





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Re: [time-nuts] GPS Jammer

[Charles P. Steinmetz]

The Power Output is 0.5 Watts and it claims a jamming range of 1-10 Meters.
Anybody think there is something wrong?


I'd expect a much greater range with a 0.5 W jammer.  But note that 
0.5 W is the "total output power" -- the "transmit power" is only 10 
dBm (0.01 W).  Whatever those terms mean.  (Does "total output power" 
include far IR and heat?)


Note that "The item is for Legal Use only!"

Best regards,

Charles





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Re: [time-nuts] They're baaaack!

[Charles P. Steinmetz]

Are LightSquared still trying to get some value from their contributions?


Of course they are.  Lightsquared ("LS") bought low-valued spectrum 
at fire-sale prices, speculating that with rule changes and waivers 
they could use it for a terrestrial broadband network, in which case 
its value would increase by a factor of 100, 1k, or 1M.  If there is 
any chance whatsoever to still reap that windfall, LS will press it.


The spectrum LS bought is allocated to the Mobile Satellite Service 
("MSS").  Until relatively recently, this spectrum could only be used 
for satellite networks.  Because mobile satellite service has never 
caught on due to the high cost of the space segment and some 
technical limitations of delivering good broadband performance by 
satellite, the value of MSS spectrum has been much lower than the 
Commercial Mobile Radio Service spectrum now used for mobile 
broadband services (pennies on the dollar, or less).


The FCC is convinced that the US will founder as a backwater and will 
be unable to climb out of the recession if it doesn't have more 
mobile broadband spectrum, and soon.  (I believe this is a faulty 
notion at best, trending toward absurd, and have articulated my 
reasons here a number of times, so I won't repeat them now.  Check 
the archives if you are interested.)  So, the FCC is racing to make 
more spectrum available for mobile broadband service.  It thought 
that the relative wasteland of underutilized MSS spectrum would be 
low-hanging fruit, so it indicated in its National Broadband Plan and 
some later decisions and Orders that terrestrial use of the spectrum 
should be considered.


Seeing the opportunity to buy cheap MSS spectrum (including buying 
some MSS companies out of bankruptcy) and convert it to a much, much 
more valuable use, thereby reaping a windfall, LS did just 
that.  However, as we have seen, the technical problems surrounding 
repurposing satellite spectrum have thrown a spanner in the works of 
the initial plan.  As I have commented here before, how the FCC and 
whoever did the LS due diligence all missed the obvious problems with 
putting powerful terrestrial transmitters adjacent to receivers 
listening to satellites is beyond me, particularly when the issue of 
SDARS (satellite radio) ancillary terrestrial transmitters 
interfering with mobile networks should have been fresh in everyone's minds.


To summarize -- LS bought cheap spectrum that nobody much wanted 
because of the difficulty of providing MSS services.  The spectrum is 
still worth about what LS paid for it, *as MSS spectrum.*  But LS 
apparently feels entitled to receive not just the value of the 
spectrum *as MSS spectrum,* but rather the value it would have *if it 
could be used for mobile broadband service.*  Put another way, they 
want their speculative gamble covered.  By whom?  Well, that would be 
us, the folks who are still in the middle of bailing out the 
speculators of the last decade.  LS now wants to swap its spectrum 
for government spectrum that would be useful for mobile broadband service.


Now, on the one hand, I think having available the "wholesale only" 
service LS says it wants to provide would be a Good Thing.  On the 
other hand, I do not think we, the people, should subsidize it.  LS 
took a gamble, and lost.  That should be the end of it.  But there 
any number of politicians who, like the FCC, are panicked that the US 
is "behind" in the mobile broadband race and think more mobile 
broadband will restart the economy (again, I say, Dream On).  So, LS 
has allies that want to cover its bet for their own reasons.


Only time will tell how it works out.  If you want to have input into 
the process, at this point lobbying your congressional delegation and 
the appropriate House and Senate committee members appears to be your best bet.


Best regards,

Charles





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Re: [time-nuts] Up And Running

[Charles P. Steinmetz]

I did put a dab of jell super glue on each of the screw heads, after they
were tightened down,  I then wiped them clean.  Maybe a bit of RTV would be
appropriate as well.


If you are trying to weatherproof an outdoor item, you will probably 
find that 3M 5200 marine adhesive/sealant is the best product for the 
job.  That said, I'd be worried about temperature/humidity cycling as 
mentioned by others, because you will never get a 100% hermetic seal 
-- so some version of a weep hole and other moisture preventive 
measures may be in order.


Best regards,

Charles





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Re: [time-nuts] Lady Heather on a Laptop

[Charles P. Steinmetz]

Chris wrote:


After some measuring my general run of thumb is "Anything you
leave plugged in and running 24x7 will cost you triple digits of
dollars (at least) over a year


Well, that's a lot of "anything."  There are 8760 hours in a year, so 
a 1 kW load will consume 8760 kWH per year.  We pay about $0.08 per 
kWH here, so a 1 kW load running 24/7 costs just over $700/year (= 
$0.70 per W per year).  That puts the "three digit" point ($100/yr) 
at ~143 W.  I leave a number of LED bulbs running 24/7, which cost 
~$2.80/yr for 4 W, ~$5.60/yr for 8 W, and ~$8.40/yr for 12 W.  Even a 
new 50" flat-screen television (119 W) would only cost ~$83/yr if 
left on 24/7, and my quad-core workstation with its huge display 
would cost only ~$250.


In another post you mentioned $0.21/kWH (you must be in California?), 
so adjust all of these by a factor of 2.625 for your location -- but 
I think the service rates in most of the US are closer to ours than to yours).


Best regards,

Charles





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Re: [time-nuts] OT: Packing and shipping of test equipment

[Charles P. Steinmetz]

Jim wrote:

As you can imagine, it turns out that foam can be too stiff or too 
soft, and that the appropriate foam density and thickness is 
dependent on both the mass of the thing being supported and the 
expected loading.


You also need to pay attantion to what parts of the item can bear how 
much loading, and from which directions -- knobs, connectors, and 
many handles can't bear much, for example -- and design the packaging 
to route loads around these features to other parts of the item that 
can bear them.  That's what all the carefully folded cardboard and 
die-cut foam in engineered pakaging do.


Take home message:  packaging is non trivial. A simple: "pack it in 
two boxes with X inches of crumpled paper or peanuts" isn't going to work.


There is no substitute for a basic understanding of the physics 
involved and the properties of available packing materials.  The 
mistake I see most often is that the contents of a box are not 
immobilized by the packing.  When the box is in motion and then 
stopped abruptly, the item has a running start to smash into the 
inside of the box and whatever stopped it.  Sometimes there is enough 
packing material to fill the space in the box but it just isn't stiff 
enough (e.g., light open-cell foam), and sometimes there isn't enough 
packing material so there is air space inside the box.  Frequently, 
both.  The buffer material for a 50 to 100 pound item needs to be 
considerably stiffer than most people think.


That said, it's not rocket science.  Large-bubble bubble wrap, 
wrapped TIGHTLY around the item in at least two directions until 
there is at least 4" on all sides of the item, is a very good start 
for anything up to about 100 pounds (6" on all sides is better by the 
time you get to 100 pounds).  You may need to use sheets of styrofoam 
insulation, heavy cardboard, or plywood to make sure loads will not 
bear on fragile parts of the item.  The bubble wrap must be taped up 
very tightly so the wrapped item feels like a monolith bursting at 
the seams, then put into a box rated for the weight of the item.


All internal space in the box must be filled with packing -- the 
bubble wrap, applied as described, will make a rounded shape, so 
peanuts or something else must be used to fill the gaps to the square 
corners of the box (I hate peanuts, so I generally use rolls of 
bubble wrap, pieces of styrofoam building insulation, etc.).


Finally, the entire contents should modestly overfill the box -- you 
should have to compress the packing to get the box shut.  When you 
do, USE TAPE FREELY.  Do not depend on tape-to-box adhesion -- wrap 
wide (at least 2"), strong tape all the way around the box 
(fiberglass filament tape is excellent), lapping the tape over itself 
the entire length of the longest side to form a tape band all the way 
around the box.  Wrap tape all three ways around the box (all three 
axes).  For smaller boxes, you can wrap once per axis, in the middle 
of the box.  For larger boxes, you need to use two or even three of 
these loops per axis, spaced out along the box.


You can also build up most of the buffer with styrofoam building 
insulation, if you prefer.  I still like to use an inch or two (all 
sides) of tightly-wrapped bubble wrap as the innermost layer.


All of this is not exactly free, and takes a bit of time -- I often 
use a whole roll of bubble wrap, sometimes more, and half a roll or 
more of tape, for a benchtop instrument or a boatanchor radio.  Plus 
a good, sturdy box.  But I have never once had an item damaged in 
shipping, since long before there was an eBay.


Best regards,

Charles







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Re: [time-nuts] Be aware of test equipment seller

[Charles P. Steinmetz]

Gary wrote:


Fedex ground is awful. Fedex air is fine.


That is our experience, as well.  It may vary from region to region 
-- the FedEx ground service uses contractors for local delivery.  Our 
contractor seems to take pride in damaging as many items as badly as 
possible.  I have witnessed them throw a heavy package from inside 
the truck to crash on the pavement (dropping from waist height inside 
the truck, so maybe 5 feet to the ground), then "rolling" the package 
(the box, I mean -- no hand truck) across the street, over the curb, 
up the walkway, and up the front stoop.  We always specify "no Fedex 
Ground" before paying and cancel transactions when sellers will not 
agree.  (For similar reasons, we specify "no USPS" for anything heavy 
-- leaving just UPS, which we have found to be the best of the ground 
carriers.  YMMV and probably will.)


FedEx Express is, perhaps, the best of the carriers in our 
experience, but that ethic does not seem to have begun to seep into 
the Ground operation.


Best regards,

Charles






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Re: [time-nuts] Subject: Be aware of test equipment seller

[Charles P. Steinmetz]

Greg wrote:

Shortly after I started bidding on eBay back in the 90's, I quickly 
learned that many of the sellers are not knowledgeable equipment shippers.


Amen.  And that is the most polite and charitable description possible.


I was surprised how the sellers would work hard to meet those requirements.


Interesting.  I have often sent basic packing 
recommendations/requests, which have almost always been ignored.


In a few instances where items weighed upwards of 100 lbs, I would 
obtain dimensions of the item(s) being sent, create a cardboard 
mockup of approximately the size and profile of the item, have my 
own container foamed-in-place  *   *   *  and send that container to 
the seller to use to ship the item to me.


Great idea, but it must dramatically raise your cost of 
transport.  With the reported scarcity/prices of T&M equipment in 
Europe that may be justified, but for domestic sales here in the 
States it could be hard to justify.


Now, after over 700 purchases on eBay, I can safely say that I have 
only received less than ten or so items that contained some form  of damage.


We have had more than double that many damaged items on fewer than 
20% of the purchases.  There was a time several years ago when eBay 
and paypal were useless at helping with not-as-described and 
damaged-in-shipment claims.  Thankfully, in the last few years they 
seem to have gotten more involved.


Never underestimate the transportation companies and their 
propensity to damage equipment.


We have seen very little damage -- in fact, almost none -- that was 
the shipper's fault.  I know it happens, but from our experience 
nowhere near as often as reports would indicate.  I think this means 
that most recipients don't know any more about packing than the 
sellers, and are mistakenly blaming the carriers for the sellers' failings.


Best regards,

Charles







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Re: [time-nuts] Recommendations for a newbie?

[Charles P. Steinmetz]

Said wrote:

you make and post negative assumptions about a seller without any 
first hand experience

 * * *
It is unfair to post that kind of negative opinion without you 
having any first hand experience with them.


This is already way out of hand -- so with this, I'm done:

I think you are over-reading my comments, intent on finding offense 
where none was given.  Please recognize that in the process, you are 
making and posting unfounded negative assumptions about me, the 
assumptions you assume that I have made, and my postings -- precisely 
what you accuse me of.


I reiterate that I said (and certainly, I meant) nothing negative 
about the seller, and made no negative assumptions and no negative 
comments.  In fact, I do have experience with him and have no 
complaints.  My point was not that one might not get what was 
described; rather, it was that I cannot tell from the 58503A listings 
exactly what is being described, or how what is described in one 
listing differs from what is described in other listings that vary 
considerably in price.  Nothing more.


The End,

Charles







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Re: [time-nuts] Recommendations for a newbie?

[Charles P. Steinmetz]

Said wrote:

Not sure why this is confusing to you, he clearly explains all the 
differences in the description


I don't see anyplace where he "explains all the differences," clearly 
or otherwise.  And as I said, ALL of the descriptions I've seen 
(including the descriptions of the Z3805-based conversions and what 
may be original 58503As) say the unit tracks 6 satellites.


Why so defensive?  I cast no aspersions on you or on the seller.  I 
just said that the descriptions I've seen do not appear to me to 
explain the great price differences and that there appear to be many 
different variants, so getting exactly what someone else got may not 
be easy or straightforward.  Prospective buyers can judge for themselves.


Best regards,

Charles







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Re: [time-nuts] Recommendations for a newbie?

[Charles P. Steinmetz]

Said wrote (re: eBay 58503As):


they work well for me, look brand-new, and came with power supply, rs-232
cable, and antenna. I think it's a 5V antenna. The unit had about 37000 on
the lifetime.

The seller has close up photos, that's what the units look like. I plugged
in the power, ran GPSCon to start an Auto-Survey, and they just worked.


Looking at the current and completed eBay listings for the 58503As 
from Hong Kong, I notice that the seller seems to have conversion 
units based on the Z3801 and on the Z3805, and some that may be 
factory 58503As.  The listing text for all of them says they have 
6-channel receivers.  Some have no PPS outputs, some have one, and 
some have two.  Some have internal AC power supplies, some have 
external supplies.  There appear to be at least two different 
rear-panel layouts.  They are priced from $260 to $999, and it does 
not seem obvious what justifies the radically different prices (aside 
from different antennas).  Based on these confusing listings, I'd be 
very reluctant to count on finding anything specific inside the 
housing (e.g, a particular OCXO) if I bought one, except possibly the 
$999 units that may be factory 58503As.


Best regards,

Charles







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Re: [time-nuts] Thunderbolt temperature sensor [WAS: Recommendations for a newbie?]

[Charles P. Steinmetz]

Bob wrote:

The strange temperature chip in the later TBolts isn't much of an 
issue. The chip is poorly located for temperature control. It only 
seems to impact the plots on Lady Heather. Trimble wasn't bothered 
enough by it to patch the firmware.


My experience is consistent with this.  While switching the chip on 
one, I used the opportunity to bring the chip temporarily outside of 
the Tbolt housing on a cable to investigate whether the Tbolt makes 
any use of the temperature data.  Neither freeze spray nor bringing a 
soldering iron near the chip, when it was outside the Tbolt housing 
and the housing was insulated from the changes in chip temperature, 
seemed to have any effect on the operation of the Tbolt, either 
normal or in holdover.  I have also run Tbolts with the new 
temperature chips for long periods, and have not observed any 
systematic differences in performance between them and units with the 
older chips, either in normal operation or in holdover.


I suspect that the temperature sensor was provided so telcom 
operators could get a rough idea of the temperature in remote 
cell-site transmitter shacks.


Best regards,

Charles







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Re: [time-nuts] REF osc distribution.

[Charles P. Steinmetz]

Luc wrote:


We have a product that have been specially design for these : NGA-DIS


Thank you for the link.  The data sheet raises a few questions:

The sine wave input level is specified as "1Vrms nominal 0.5V Peak to 
peak."  Of course, 1Vrms is ~2.8Vp-p.  It is not clear what this 
specification means.


Gain and noise are not specified, nor is isolation from output to 
input or from the outputs to each other.  These are parameters that 
many buyers will want to know.


Have you characterized the NGA-DIS for phase noise?  That is also a 
parameter many buyers will want to know.


Does each output have its own output amplifier, or does one amplifier 
drive multiple outputs through individual build-out resistors?


Does the NGA-DIS use op amps, or discrete circuitry?

What is the price?

Best regards,

Charles







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Re: [time-nuts] Thunderbolt temperature

[Charles P. Steinmetz]

Michael wrote:

I'm still not entirely sure this is a good idea though, seems like a 
low-temp oven for the whole tbolt would be better if you want 
thermal stability.


Precisely because it is not clear that holding the backplate of a 
Tbolt at a constant temperature is the best way to keep the interior 
of its crystal oven at the most constant temperature (which is the 
ultimate goal), I mounted mine on thermally insulating standoffs in a 
cast aluminum box with about 1" of clearance on all sides, and 
control the air temperature inside the cast box.


For another Tbolt mounted similarly, I control the surface 
temperature of the cast box, which seems to work equally well.


In both cases, I adjust the controller for whatever measured 
temperature produces a Tbolt internal temperature reading (via the 
Tbolt's DS1620) of about 45C -- safely above any ambient temperature 
to which the mounted units will be exposed, to avoid the need for 
active cooling (Peltier, etc.), but not excessively so, to keep the 
internal electronics as cool as is practicable.


Best regards,

Charles







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Re: [time-nuts] Thunderbolt distribution amplifier needed

[Charles P. Steinmetz]

Remember  *  *  *  these DAs are designed be unity gain and to 
handle approximately 1 volt p-p so be carefull of clipping if you 
drive much more than that level or alternatively, pad down the input 
to a 1 volt level.


Also, video DAs are designed to drive 75 ohms (the video world's 
standard distribution impedance), so you will get additional 
attenuation at the output if you are driving 50 ohms, and you may get 
current clipping.  That said, some video DAs work quite well at 10 
MHz/50 ohms/+13 dBm (= 1 V rms = 2.8 V p-p) if you modify the 
internal input and output impedances.  In some cases, you can reduce 
the added phase noise by reducing the LF gain.


Best regards,

Charles







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Re: [time-nuts] T-Bolt Temperature

[Charles P. Steinmetz]

I have two Thunderbolts that I'm monitoring with 
Lady Heather.  The temperature on the older unit 
(MFG 2/26/2004) seems to track the 
environment.  The newer one (MFG 11-24-2004) 
shows 44.75 °C and only changes in increments of exactly 1°.


Sounds like the newer one has the newer 
temperature sender chip (DS1620).  Briefly, the 
chip manufacturer changed the innards and the 
high-resolution display feature.  Trimble did not 
update the Tbolt, but continued to use the newer 
version of the chip.  IIRC, chip revisions prior 
to E work properly in the Tbolt, while Rev. E 
(and later, if such exist) do not.  The cure is 
to replace the IC with an older revision chip.


The archive has lots of information on this.

Best regards,

Charles











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Re: [time-nuts] T-Bolt output harmonics

[Charles P. Steinmetz]

john wrote:

Or they [line harmonics] were cancelled by running the TBolt and 
spectrum analyzer from the same AC circuit.  That's tripped me up before.


Good thought, although probably not the case here.  The Tbolt is 
supplied from a "double conversion" UPS with an output that is not 
referred to ground, while the SA runs straight off the mains.


Best regards,

Charles







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Re: [time-nuts] T-Bolt output harmonics

[Charles P. Steinmetz]

Grant wrote:

I tamed the provided switching power supply noise with some L's and 
C's, and am now looking at the 10MHz output on a spectrum analyzer. 
Here is what I measured:


10MHz   +9dbm
20MHz-50dbm
30MHz   -37dbm
no obvious higher harmonics
broad noise envelope at 60 > 75MHz @  -60dbm peak

Are these results typical or might I have an adjustment or other problem?


I unhooked my primary Tbolt from the distribution system and ran it 
straight into the 50 ohm input of a SA.  My results:


 10 MHz +12.66 dBm
 20 MHz -57.85 dBc
 30 MHz -59.54 dBc
 40 MHz  below noise floor
 50 MHz -67.78 dBc

My noise floor was about -80 dBm (~ -90 dBc).  I saw nothing else 
above this floor from DC to 150 MHz except for 60 Hz (at -83 
dBc).  Surprisingly, the power line harmonics were all below the noise floor.


Best regards,

Charles







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Re: [time-nuts] Active antennas for a Thunderbolt...

[Charles P. Steinmetz]

Chuck wrote:


I don't quite know what to say about that.  Trimble seems to think that bullet
antenna is the right thing to use.  Somehow, I would think they should know.


I normally use a choke-ring survey antenna, but I also have a Trimble 
Bullet III, P/N 41556-00 (RoHS version is P/N 57860-10) -- which is 
the antenna that Trimble recommended for use with the 
Thunderbolt.  IME, at 35-40 north latitude it works OK indoors (with 
a plaster ceiling and asphalt tile over wood roof between it and the 
outside), and flawlessly out in the semi-open (some trees closer than 
you'd like) with 100 feet of good 75-ohm coax (most birds have a c/n 
of 48 dB or more).  A Symmetricom cone timing antenna works pretty 
much the same, with about 2 dB lower c/n.


Best regards,

Charles






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Re: [time-nuts] Zero-Crossing Detector Design?

[Charles P. Steinmetz]

Michael wrote:

One circuit I was recommended when I was looking for ideas uses a 1M 
resistor to feed the output of the inverter back to the input to self-bias


That works OK, but you have to be careful.  Without an input signal, 
there can be excessive quiescent current through the inverter (Vcc to 
ground) -- for which it was not designed.


Best regards,

Charles







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Re: [time-nuts] HP 117/10509a

[Charles P. Steinmetz]

Don wrote:


the fet breakdown voltage has of course got to be high enough.


If the nuvistor is used as a common-cathode or common-grid amplifier, 
you can cascode the fet with a bipolar to extend its drain voltage 
range.  You will need to come up with an appropriate bias source for 
the bipolar.  Generally, you would want at least 10-15 volts across 
the FET channel.


Choose an appropriate JFET (transconductance, drain current, and 
gate-drain voltage similar to the nuvistor at the nuvistor's 
operating point).  You can add degeneration (source resistance) to 
lower the FET's transconductance if it is higher than the nuvistor's.


Best regards,

Charles





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Re: [time-nuts] TimePod, cross-correlation fun and measurements

[Charles P. Steinmetz]

Joe wrote:


I was recently reading the manual for the TimePod. It looks quite
nice. I'm curious as to the price.


http://www.miles.io/

Best regards,

Charles







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Re: [time-nuts] NTGS50AA glitches

[Charles P. Steinmetz]

Dan wrote:

The attached LH plot shows what happened when it was moved slightly 
on the bench two or three times.  What surprises me is that the DAC 
plot remains offset after everything else has settled.


The movement event(s) appear to coincide with about 3 hours of 
significant temperature events.  Both physical jostling and 
temperature may have an observable effect on the required EFC 
voltage.  IME, the ~2 mV ECF shift seems somewhat high for normal 
jostling, but not beyond reason.


Best regards,

Charles







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Re: [time-nuts] LightSquared in the news again

[Charles P. Steinmetz]

Chris wrote:


Actually LightSquared is an investment firm.  They don't make any
"technology product".   The company is run by a banker.  Had their plan
worked they would have ben in effect a radio wholesaler buying from
producers and sellers to retailers who would then sale to end users.  They
never intended to make or invent anything.  Basically they would do deals
and swap cash.   From the start, really their plan was always to have more
lawyers than engineers.


Not entirely accurate.  The holding company, Harbinger, is an 
investment firm/hedge fund.  The operating entity (LightSquared) is a 
facilities-based provider.  It already owns one or more satellites, 
and has plans to build a terrestrial network.  Its business model is 
wholesale -- that is, it would sell capacity to other entities, not 
to retail customers.  But that capacity would be on its own 
facilities-based network, not acquired from other wholesalers (except 
perhaps at the beginning, as it was building out its own 
network).  Of course, that is all in limbo now.


Best regards,

Charles







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[time-nuts] LightSquared in the news again

[Charles P. Steinmetz]

From today's communications news (fair use):

LightSquared stressed its intention to deploy a nationwide 4G 
wireless broadband network, during a meeting with Angela Giancarlo, 
chief of staff to FCC Commissioner Robert McDowell. The commission 
has some legal and policy responses it can take "to address the 
inability of a limited number of GPS receivers to operate properly in 
spectrum that has not been allocated for GPS use," the company said 
in an ex parte filing. It said the actions proposed in the 
commission's Feb. 15 public notice revoking its ancillary terrestrial 
component "are disproportionate and inappropriate, especially in 
light of the current administrative record."







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Re: [time-nuts] Why 9,192,631,770 ??

[Charles P. Steinmetz]

Don wrote:


It's interesting to note (to ask?): When did someone get smart enough to
start measuring 1/86 thousandth of a day


That is generally considered to be the 10th/11th century Persian 
Muslim mathematician and astronomer, Abu al-Rayhan Muhammad ibn Ahmad 
al-Biruni (a.k.a. Alberonius and Al-Biruni).  His eclipse data was 
accurate enough that it was used in the late 18th century to help 
quantify the acceleration of the moon, and is still used by astronomers today.


Best regards,

Charles







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Re: [time-nuts] Wilkinson TDC

[Charles P. Steinmetz]

Bruce wrote:

The essentials of a Wikinson TDC can be simplified to the attached 
circuit which only requires the addition of a zero crossing 
comparator to monitor the voltage across the capacitor C1.


A few refinements to improve the capacitor charging current 
switching transitions and the addition of an upper voltage clamp 
together with the use of faster transistors may be useful.


The HFA3096 transistor array (3 NPN + 2 PNP) should do nicely.  My 
simulations show a small but definite improvement in the current 
switching transitions.


BTW, the PNPs in an HFA3096/3128 also pretty much solve the Cb-e 
feedthrough in a Wenzel-style squaring circuit, giving pretty flat 
tops on the high output pulses without resorting to diode isolation 
or other secondary techniques.


Best regards,

Charles





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Re: [time-nuts] Racal-Dana tactile switches

[Charles P. Steinmetz]

Stewart wrote:


It's a design fault and eventually all of them will fail.


I'm not convinced of that.  There has been substantial discussion of 
Racal switches on the list in the past, and I suggested at one point 
that the failure mechanism (dry, cracked "rubber") could be related 
to the counter manufacturing process -- in particular, soldering 
and/or cleaning of the front panel PCBs.  In my experience with 1992s 
(quite extensive), I have found that (i) in some counters the 
switches never seem to fail, while (ii) if one switch fails in a 
counter, all of the others are not long for the world.  There does 
not (IME) appear to be any correlation with the color of the switch 
body or the markings on the switches.


Then again, I suppose making switches that won't survive every 
possible abuse during whatever soldering and cleaning processes a 
customer might use could be considered a design fault


Best regards,

Charles







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Re: [time-nuts] Lucent 40 dB Antenna

[Charles P. Steinmetz]

Gary wrote:

Most of those no antenna rules can't be enforced. They can control 
the color of the antenna. Yes, really. For example, CONUS, you can 
have any number of 1 meter dishes. You might have to paint the dish.


I believe Gary is referring to the FCC's OTARD (Over-the-Air 
Reception Devices) Rule, 47 C.F.R. Section 1.4000, which (with some 
exceptions) preempts local restrictions that impair the installation, 
maintenance, or use of antennas used to receive video programming or 
certain point-to-point wireless signals (e.g., wireless "last mile" 
Internet service).  However, it does not preempt local restrictions 
on antennas used for GPS, AM or FM broadcast reception, SWL, 
satellite radio, etc., etc.


For a quick guide to the OTARD Rule, see 
.


Best regards,

Charles







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Re: [time-nuts] WWVB phase modulation test April 15-16

[Charles P. Steinmetz]

Hal wrote:


How many of you have used the Tek scope-probe to BNC adapter?  I tried a bit
but couldn't find anything on the web.  The idea was (roughly) that you put a
BNC Tee in the line you wanted to watch and this magic gizmo on the Tee.


I have some.  I don't use them often, but they are very useful on 
occasion (when you want to insert a sampling port in coax with 
minimal disturbance to the line).  You normally use them with 10x 
probes to minimize the capacitive loading at the sampling port.  They 
used to appear on eBay quite frequently for $2-$5 each, but for the 
last year or so sellers seem to be very proud of them.


Note that you need one that matches your probe tip (5 mm, 3.5 mm, or 
2.5 mm ground sleeve).


Best regards,

Charles







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Re: [time-nuts] Lucent 40 dB Antenna

[Charles P. Steinmetz]

Chris wrote:


Where are you placing your antenna?  I'm curious because you say the
choke ring helps.  Is it close to the ground, near a building?  What
might be the cause of the muiltipath that the choke ring is helping
with


I've been working with RF long enough not to expect easy answers when 
it comes to multipath.  It's pretty much always there, sometimes in 
sufficient quantity to be really troublesome, other times (as with 
GPS at my location) enough to notice but not to be really troublesome.


Typical suburban neighborhood, 2-story brick houses on ~80-foot 
lots.  The antennas have been tried (i) on the second floor (under a 
plaster ceiling + asphalt shingle roof); (ii) in the attic (under the 
roof only); and (iii) on a mast about 15' above the roof peak (~45' 
AGL).  The c/n improves ~ 7 dB going from (i) to (ii) and another ~2 
dB going from (ii) to (iii) for all antennas, while the relative 
advantage in positioning and deviation of the choke ring is 
essentially unchanged.  After experimenting, I installed the choke 
ring antenna in the attic peak.


A ground plane placed under the mag mount and the Bullet 3 did not 
improve the positioning or deviation.


Best regards,

Charles







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Re: [time-nuts] Lucent 40 dB Antenna

[Charles P. Steinmetz]

Chuck wrote:


My Lucent antenna arrived today.

Has anyone compared this antenna with the mushroom that
came from China with the used Thunderbolts???


I have five GPS antennas -- a Garmin mag-mount puck designed for 
vehicular use, a Garmin marine mushroom, a Lucent "timing" antenna 
like yours, a Trimble Bullet 3 (the antenna specified by Trimble for 
use with the Tbolt), and an Aerotenna choke-ring survey 
antenna.  Deployed in the same location, they all give very similar 
signal reports from the Tbolt and track the same number of satellites 
(remember, the Tbolt reports the carrier/noise ratio, not raw signal 
strength, and c/n is closely correlated with the signal environment 
at the antenna location unless an antenna has way too little gain or 
a very noisy preamp).  This suggests that they all have sufficient 
gain and low enough noise to work properly with a Tbolt.


The one difference I observe is that the choke-ring antenna shows 
consistently less variability in its surveyed position, and lower 
deviation of both the 10 MHz and pps, than all of the others.  I 
assume that this is due to reduced multipath, but I have no way to verify it.


Best regards,

Charles







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Re: [time-nuts] Austron 2201, Tbolt, HP 3801 comparison question

[Charles P. Steinmetz]

Ulrich wrote:


The Smartclock in difference seems to be able to adapt regulation
parameters to its "measurements" of ocxo stability and long term drift.


I do not know any details about Smartclock, but I believe one of the 
things it does is to adjust the oscillator disciplining parameters 
(primarily the loop time constant, I suspect, but perhaps more) to 
allow 3801s to reacquire lock quickly after a holdover event (or at 
startup), then switch to parameters that reduce the deviation once it 
is firmly locked.  You have to do that manually with a Tbolt if you 
want both quick lock and best stability once locked.


It may also do as you suggest -- use heuristic methods to tweak the 
"low deviation" discipline parameters -- but I do not know if that is 
the case or, if so, if it is better than Kalman filtering.


Best regards,

Charles







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Re: [time-nuts] Distribution amp - Use a video amp unit ?

[Charles P. Steinmetz]

Bruce wrote:


The above reverse isolation [~35 dB] is about 25dB lower than I would expect.


D'oh!  Bruce is right -- I calculated the reverse isolation 
incorrectly.  I had only been expecting 40 dB, so I didn't question 
the result.  The breadboard actually measured nearly 63 dB.



Stable operation at unity gain is necessary if a feedback capacitor is used.


The Miller capacitance of the output transistors sees to that (with 
an even greater phase margin when a faster transistor is used for Q1).


An LM329 has similar noise without the dissipation of the internal 
heater in the LM399


I know.  I just particularly like the 399, and have a pile of 
them.  I rationalize using it in this case by noting that the range 
of frequencies where phase noise of the DA is important includes sub- 
to low-Hz frequencies at which thermal effects could make the 
unheated 329 significantly noisier (though if you keep drafts off 
both of them, it might not be by a large amount).


Best regards,

Charles







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Re: [time-nuts] Distribution amp - Use a video amp unit ?

[Charles P. Steinmetz]

Randy wrote:

if one is distributing 10 Mhz, does it really 
matter what the circuit does at 300 and 900 Mhz??


That depends on what it is feeding and what noise 
and other signals are getting to the DA 
input.  Some synthesized 10 MHz sources produce energy well above 10 MHz.


I consider nonmonotonic behavior to be a design 
flaw in general (except where it is specifically 
desired or you are up against the bleeding edge 
of technology and it can't be avoided), so I 
eliminate it at every opportunity as long as the 
fix doesn't cause worse problems.  In this case, 
the nonmonotonicity is cured by replacing an 8¢ 
transistor with a 16¢ transistor, and some other 
small benefits are realized at the same time, so 
I say it's 8¢ well spent.  Nearly a whole dollar 
extra for a 12-output DA.  The noise bump is 
cured by restricting the 3 dB bandwidth to ~80 
MHz, which does not affect the 10 MHz but may 
help the receiving instrument if it is sensitive 
to VHF noise (although the magnitude of the bump is not large).


I consider these good prophylactic design 
measures.  Practicing them keeps you out of 
trouble that you might not even know was 
threatening, whether or not it makes a practical 
difference WRT a particular design.


Best regards,

Charles







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