Re: [time-nuts] uC ADC resolution (was: Poor man's oven)

[Logan Cummings]

Hi Folks,

   This discussion of temperature measurement with ADCs has crossed into my
professional life and without being too much of a commercial plug just
wanted to mention that I support Linear Technology's temp-to-bits family of
ICs: LTC2983, LTC2984, LTC2986.

   Overview: each part has 3 24-bit delta-sigma ADCs along with low leakage
input buffers, excitation sources, an internal mux, and a small
linearization engine. They can measure just about any type of temperature
sensor and digitize it to deg C or F with really good accuracy. Ultimately
accuracy will depend on the sensor, your implementation, environmental
conditions, etc. but the parts have a lot of features that help you get the
most out of a given sensor.

   They aren't super cheap (Digi-Key pricing is particularly bad, if you
can order from Linear direct it's much better) but they are to my knowledge
by far the simplest way to interface to a thermistor, RTD, thermocouple,
etc. and get <1degC accuracy.

Ping me off-list if you want to know more or have an application question
in mind.

-Logan
http://www.linear.com/product/LTC2983

On Wed, Jun 7, 2017 at 8:04 PM, jimlux  wrote:

> On 6/7/17 7:35 PM, Bob kb8tq wrote:
>
>> Hi
>>
>> Metal actually makes things a bit worse since it has a lower thermal
>> resistance than glass.
>> This is also why a high performance dewar is made from glass rather than
>> metal.  Yes, you
>> can go to weird stuff like titanium (it has been done). You can’t afford
>> that ….
>>
>> If you fill the entire dewar with a heat conductor you make things worse
>> still. The idea is to
>> *block* heat flow out of the heated area. Even without fill,  the wall of
>> the dewar goes from the outside
>> world to the heart of the heated area. It is the perfect “sneak" path
>> into the oven. Actually
>> it’s not that much of a sneak path since it’s a well known effect :)
>>
>> Again, none of this is particularly original. Take a hammer to any dewar
>> based OCXO and
>> the details are going to be similar.
>>
>>
> And the wires provide a thermal path - you've got to get power to it and
> the oscillator signal out.
>
> In dewar OCXOs (like the USOs made by APL), the leads are essentially the
> only thermal path in/out.
>
>
> BTW, you don't want to do oil filled. All oil filled electronics (unless
> welded closed) inevitably leaks, oozes, or otherwise puts oil on the
> outside. If you *must* have oil, then use solid, uninsulated wires to
> penetrate the surface of the oil. Otherwise you'll gain new appreciation
> for what capillary action is.
>
>
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Re: [time-nuts] GPS first LO need to be locked?

[Logan Cummings]

Dave,

I was able to find [2] here:
http://web.stanford.edu/group/scpnt/gpslab/pubs/papers/Akos_IONGPS_2003_3FreqRX.pdf

[3] was harder, and I don't have a link but a google search for the title
in quotes got me a link on semanticscholar that let me download the PDF.

Interesting stuff!

Hope that helps,
-Logan

On Fri, Mar 31, 2017 at 9:17 AM, David C. Partridge <
david.partri...@perdrix.co.uk> wrote:

> links [2] and [3] give 404 errors
>
> Dave
>
> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Attila
> Kinali
> Sent: 31 March 2017 12:35
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] GPS first LO need to be locked?
>
>  [2] "A Prototyping Platform for Multi-Frequency GNSS Receivers", by Akos,
> Ene and Thor, 2003 http://waas.stanford.edu/~wwu/papers/gps/PDF/
> AkosIONGPS033FreqRX.pdf
>
> [3] "Design of a GPS and Galileo Multi-Frequency Front-End", by Parada,
> Chastellain, Botteron, Tawk, Farine, 2009 http://202.194.20.8/proc/
> VTC09Spring/DATA/04-04-01.PDF
>
>
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Re: [time-nuts] FE-405B Reprogramming

[Logan Cummings]

Thanks Bob,

   I figured if it was that easy someone else would have already done
it. Went looking for a schematic and found Tom's page describing the
architecture at a high level and with ADEV plots providing evidence of said
architecture. Good block diagram from an FEI presentation at the bottom of
the page http://www.leapsecond.com/pages/fe405/

  Takeaway: no, can't be done - 5MHz DOCXO clocks a DDS which outputs
at 15MHz feeds into a PLL steering a standard 15MHz VCXO which then
provides the output directly.

  Very interesting architecture and gives me some food for thought, but
does not solve the 15 != 10 problem Nick was facing.

Cheers and thanks again!
-Logan

On Wed, Jun 8, 2016 at 3:06 PM, Bob Camp <kb...@n1k.org> wrote:

> Hi
>
> The 405 appears to have some “bandpass” elements in it. You can not tune
> it over a wide range.
>
> Bob
>
> > On Jun 8, 2016, at 3:08 PM, Logan Cummings <logan.cummi...@gmail.com>
> wrote:
> >
> > Hi All,
> >
> >Nick's request for a divide-by-three circuit to get his FE-405B to
> > output a 10MHz signal got me thinking - didn't want to threadjack.
> >
> >I had assumed that the FE-405B's DDS output and FE-5680 compatibility
> > made it a good candidate for output frequency reprogramming. Has anyone
> > determined that this is not possible? My biggest concern was that if the
> > internal crystal is also at 10MHz you'd get bad spurs trying to output
> the
> > DDS at the same frequency..
> >
> >Does anyone know if the FE-405B uses the original FE-5680 DDS circuit
> > or the more recent one that is only narrowly (EFC) tunable over the
> serial
> > interface? Would be great to have a stable reference at 1, 5, 10, etc.
> MHz.
> >
> >
> > Any info/references on the FE-XXX internals would be appreciated!
> >
> > Thanks,
> > -Logan
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[time-nuts] FE-405B Reprogramming

[Logan Cummings]

Hi All,

Nick's request for a divide-by-three circuit to get his FE-405B to
output a 10MHz signal got me thinking - didn't want to threadjack.

I had assumed that the FE-405B's DDS output and FE-5680 compatibility
made it a good candidate for output frequency reprogramming. Has anyone
determined that this is not possible? My biggest concern was that if the
internal crystal is also at 10MHz you'd get bad spurs trying to output the
DDS at the same frequency..

Does anyone know if the FE-405B uses the original FE-5680 DDS circuit
or the more recent one that is only narrowly (EFC) tunable over the serial
interface? Would be great to have a stable reference at 1, 5, 10, etc. MHz.


 Any info/references on the FE-XXX internals would be appreciated!

Thanks,
-Logan
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Re: [time-nuts] uBlox (US) reseller recommendation?

[Logan Cummings]

Hi Nick,

We buy a lot of positioning receivers from uBlox regularly at work, and
have always bought directly from them. Their online store carries
everything and gives discounts for >10 units but you may get a slightly
better price talking to a sales rep given your EAU will be greater than the
10 units you buy at a time.

Hope that helps,
-Logan

On Mon, May 16, 2016 at 7:25 AM, Nick Sayer via time-nuts <
time-nuts@febo.com> wrote:

> Anybody done business with a reseller of uBlox GPS timing receivers (in
> the US) that they like a lot? Looking to do Qty:10 or so on an irregular
> basis. I haven’t actually picked *which* one I want just yet, as I want to
> design around availability and price.
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Re: [time-nuts] Trimble SMT 360

[Logan Cummings]

Hi Michael, Bob,

 I had been very curious about this myself - the new ICM SMT 360
modules at first glance seem like a great deal - < $50 and 10MHz TCXO
disciplining built right in.

 I came across this paper which compares the older (GPS-only) ICM SMT
to a LEA-6T - the Trimble fares poorly in their testing.  The graphs don't
show an issue quite like yours Michael, so I'd be curious about the line of
questioning Bob brings up, how many satellites are being used by the
receiver - say in GPS-only mode?

http://www.imeko.org/publications/tc10-2013/IMEKO-TC10-2013-028.pdf

Does anyone else have comparative experience with the new SMT modules
from Trimble? RES or ICM?

Thanks,
-Logan

On Tue, Apr 19, 2016 at 4:01 AM, Bob Camp  wrote:

> Hi
>
> The two plots shown appear to be identical. If they are actually two
> different
> runs, the problem repeats very closely.
>
> If the GPS is not in position hold *and* the antenna is less than ideal -
> That’s
> the sort of thing you may see. Essentially it’s got two locations it
> “thinks” are
> correct. Another possibility is a position hold situation with a very low
> satellite count.
> As a single observed satellite goes in and out of multi path, the solution
> goes all over the place.
> Again, you need a challenged antenna for this to happen. Pretty much all
> of this
> would be apparent from the normal messages out of the part.
>
> Bob
>
>
>
> > On Apr 18, 2016, at 10:13 PM, Michael Wouters 
> wrote:
> >
> > Does anyone have  experience with the Trimble SMT 360 ?
> >
> > I bought some of these four or five months after they were released.
> During
> > testing, the 1 pps output evidenced a problem, as shown in the attached
> > plot (the 1 pps is being measured against a Cs  beam standard), which is
> > not sawtooth-corrected. While there are longish periods of nominal
> > operation, the receiver seems to hop between two solutions.  This
> behaviour
> > is well out of specification.
> >
> > When I contacted Trimble support, they said that the firmware in the
> > receivers was very early, and replaced the receivers. However, the
> problem
> > was still evident with the new firmware. Trimble did not respond to
> further
> > emails.
> >
> > I tried many things to isolate the problem, including restricting the
> > receiver to GPS-only but I was unable to make an improvement.
> >
> > I would like to know if anyone else is operating an SMT 360 and if they
> > have seen any similar behaviour.
> >
> > Cheers[image: Inline image 2]
> > Michael[image: Inline image 1]
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Re: [time-nuts] Fast risetime pulse generator

[Logan Cummings]

Hi Bill,

Lots of resources out there on EEVblog forums and elsewhere. One nice
alternative to the avalanche pulser is a very fast comparator like the
ADCMP580 from Analog Devices. Generate a pulse of whatever width you want
with slower gear, and have the comparator sharpen the edges.

See here:
http://www.eevblog.com/forum/testgear/inexpensive-diy-50ps-ultra-fast-pulse-generator/
and
http://www.starlino.com/build-a-really-fast-pulse-generator-50ps-rise-time-using-an-ultra-fast-sige-comparator.html

For a couple of examples. The EEVblog thread also has a link to info on an
avalanche pulser using a transistor that avalanches at 30V rather than 70+.

-Logan

On Tue, Apr 12, 2016 at 2:28 PM, Alan Melia 
wrote:

> Bill, Avalanche pulse gens only require high voltage because of the high
> VBRcbo and the gain of normal NPN transistors. I cant find the reference
> now it might have been a 1970s Ham Radio but if you use the same circuit as
> Jim but put an NPN "upside down" that is emitter where the collector is in
> Jim's circuit you can fire off fast pulses from a 12v supply, instead of
> requiring 70 to 100v. I do wish I could locate the source as I have had
> several arguments about it :-))in the nicest possible way of course.
>
> Alan
> G3NYK
>
> - Original Message - From: "BIll Ezell" 
> To: 
> Sent: Tuesday, April 12, 2016 9:30 PM
> Subject: [time-nuts] Fast risetime pulse generator
>
>
>
> (cross-posted to volt-nuts)
>> After paying only limited attention to this topic, I suddenly have a need
>> for a pulse generator that has <150 ps risetime and a pulse width of at
>> least 2 ns. 100mv amplitude or more is fine. I've looked at the classic Jim
>> Williams avalanche generator, but I don't want to have to deal with the
>> (relatively) high voltage source needed.
>>
>> I've done microwave design using Gunn diodes, so I'm drawn to using a
>> step-recovery diode. The topology seems very straightforward, and I can
>> build it right onto a BNC connector, no PCB.
>>
>> I'm thinking using an SMD835 diode, biased at ~1ma. The (sketchy)
>> datasheet claims a T of 20 nsecs and a Tr of 85 ps, Cj of 0.4 to 0.8 pf.
>>
>> Questions:
>>
>> The obvious, is it reasonable?
>>
>> Is the bias current reasonable? I'm assuming the bias current is actually
>> dependent on the repetition rate, you need enough current to replenish the
>> charge within one pulse cycle. I suppose I could compute it from the stated
>> junction capacitance, but I'm not sure that's the only factor.
>>
>> Will the stored charge actually give me the desired transition rate into
>> 50 ohms? Hmm, again I should be able to compute this, but any other factors
>> ignoring the non-diode ones like cap inductance?
>>
>> How should I compute the coupling cap from the diode to the load? Use the
>> impedance at the pulse rep rate? Seems reasonable. BTW, I don't care about
>> droop in the  pulse, just the risetime.  (measuring overshoot in an HF
>> amp). Again, just want to verify that the obvious answer is the correct
>> one. I clearly need to be very careful about the inductance.
>>
>> Thanks, Bill
>>
>> --
>> Bill Ezell
>> --
>> The day Microsoft makes something that doesn't suck
>> will be the day they make vacuum cleaners.
>> Or maybe Windows 10.
>>
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Re: [time-nuts] LEA-M8T

[Logan Cummings]

Hi Bob,

Can't speak to jitter accuracy but the M8 series is definitely not the
same receiver in the 6 series. As you probably know, M8 introduced
multi-GNSS support so in addition to GPS you have Beidou and Glonass
satellites.

 At work we've had some gnashing of teeth about the wider filter
passband requirements for multi-GNSS support since we're operating in a
noisy environment, but I have nothing further on degraded performance when
using only GPS.

 Would be interesting to let it have all the constellations and see
what happens.

-Logan

On Wed, Apr 6, 2016 at 10:04 AM, Bob Stewart  wrote:

> I recently bought a number of LEA-M8T receivers and I have to say that I
> am unimpressed, so far.  They don't survey to the same reported accuracy as
> the LEA-6T in the same amount of time.  They certainly aren't better in the
> jitter after sawtooth correction.  So, have I managed to overlook some new
> field, or are they just not the same receiver as the 6T?  I did shut all
> sats off except GPS sats.
>
> Bob - AE6RV
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Re: [time-nuts] Holdover recovery

[Logan Cummings]

My Italian is not very good, but I think this is the English translation
via ITU:

https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.2253-2012-PDF-E.pdf

-Logan

On Mon, Apr 4, 2016 at 1:10 PM,  wrote:

> Here the italian version:
>
> http://www.crit.rai.it/eletel/2012-1/121-2.pdf
>
> Luciano
> www.timeok.it
>
>
> On Mon 04/04/16 21:28 , Magnus Danielson 
> wrote:
>
> > Hi Hal,
> >
> > On 04/04/2016 05:39 AM, Hal Murray wrote:
> > >
> > > Has anybody studied what happens when a GPSDO comes out of holdover?
> Has
> > > anybody seen any specs? I don't think I have.
> > >
> > > I think you have a choice of quick recovery for time or frequency, but
> > you
> > > can't get both.
> > >
> > > Suppose your setup has been in holdover for a while. The frequency is
> > > slightly off. The time offset of the PPS pulse will be the integral of
> > the
> > > frequency offset.
> > >
> > > What happens when you come out of holdover? If you fix the frequency,
> > the
> > > PPS will stay off.
> > >
> > > Suppose the PPS has drifted by 1 ns. If you correct that in 1 second,
> > the
> > > frequency will need to be off by 1E9 during that second.
> >
> > The RAI laboratory in Torino have made such tests and published
> > measurements and recommendations. For a long time it was only available
> > in italian, but there is now an english version available.
> >
> > Cheers,
> > Magnus
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> >
> >
> > Links:
> > --
> > [1]
> >
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Re: [time-nuts] Home-brew GPSDO

[Logan Cummings]

Hi Nigel,

Mostly just chiming in because I'm planning to do something very
similar, disciplining or tuning a VCO to a precise frequency based off GPS
PPS - with a Due (Atmel SAM3x8E).

In my case the control voltage is much wider range, so I'm forced to
use an external DAC - I picked one that's I2C controllable - easy to
interface with the Due.

As far as control loop improvements go, I haven't implemented them yet
but my plan was to combine the frequency counting you describe above, with
some form of sub-period phase offset measurement. After having no luck
trying to find some links to share, I think the terms to search for are TAC
(Time Amplitude Converter) and the digital version, Time Digital Converter
(TDC). The ones I was looking at implementing are essentially the ramp
interpolator described here:
https://en.wikipedia.org/wiki/Time-to-digital_converter

 I was planning on using the Due's ADC to measure the voltage on the
integrator capacitor, but hadn't decided yet about a "good" current source
vs. a series resistor on the output of an XOR or DFF phase comparator to
put charge on the capacitor.

 Hopefully someone else can chime in with some better links and circuit
descriptions. Fairly certain this has been discussed a bit on the list and
when I have some time I'll be searching the archives.

Cheers,
-Logan

On Wed, Mar 16, 2016 at 9:47 PM, Nigel Vander Houwen <
timenuts-nige...@nigelvh.com> wrote:

> Hello All,
>
> Thanks to the advice earlier, I’ve gotten my HP 10544A OCXO working well,
> and close enough in frequency that the EFC is useful. I’ve started work on
> putting together a home-brew GPSDO. In short, it’s an Arduino Due, and a
> u-blox MAX-7 module. (I may think about grabbing a LEA module in the
> future, but the data sheet reference to PPS accuracy looks about the same,
> so for now, the MAX-7 will work alright).
>
> The Arduino Due has some nice 32bit timer/counters on board, and I’m
> clocking one of them from the 10MHz output from the 10544A. The PPS output
> of the GPS goes into a hardware trigger pin, so I can trigger a capture of
> the counter value in hardware without the delay uncertainty of trying to
> capture it in an Interrupt Service Routine.
>
> I’m using one of the Due’s on board 12-bit DACs (Not PWM) to feed the EFC
> input of the 10544A. The Due’s DAC output is only 0-3.3V, which is a fair
> bit less range than the -5 to +5V of the EFC input. Since the EFC input is
> inverting, I’ve got the crystal coarsely set just slightly high in
> frequency, and the DAC operating from 0-3.3V will bring it down to where it
> should be.
>
> To put a VERY basic disciplining scheme in place, I’ve set it up so I’m
> capturing the clock cycles of the 32bit counter (clocked from the 10MHz),
> every second on the PPS trigger, adding them up over 420 seconds (a few
> seconds shy of the 32-bit counter overflowing), and then taking the
> average. If it’s high, voltage goes up, if it’s low, voltage goes down.
>
> I haven’t yet put in place, but I plan to:
> Reconfigure the u-blox module into stationary position mode, which should
> help with accuracy over the default mode
> Implement a survey routine to average some number of position samples on
> request/on power up?
> Implement different disciplining modes, at power on, give the oven time to
> warm up, when first disciplining, average over shorter intervals to hone in
> on the proper EFC level quicker, move to longer intervals for long term
> disciplining.
>
> I would like input on the control loop though. I can’t say I’ve done a lot
> of control loop theory, but I imagine folks have good ideas for better ways
> to discipline this crystal than just taking really long averages.
>
> I haven’t put labels on the case yet, but here’s an album with some photos
> of the build so far. I still need to add a buffer amplifier for the 10MHz
> output so as to not load down the crystal too hard, but otherwise I’m
> fairly satisfied with the build so far.
> http://images.digitalnigel.com/index.php/GPSDO-Build <
> http://images.digitalnigel.com/index.php/GPSDO-Build>
>
> Anyway, thanks again for the insight earlier regarding tuning the oven
> temperature, and I look forward to your thoughts regarding this build.
>
> Thanks,
> Nigel
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[time-nuts] Valpey-Fisher VFT22H OCXO Output

[Logan Cummings]

Hi All,

 Curious what could give this waveform (attached) - I presume this is
not correct output for this oscillator (surplus/salvage from Harris
Constellation receiver).

 Frequency looks OK with +2V EFC but output looks like neither sine nor
any CMOS I've seen into 10Mohm (first capture, scope probe alone) or 50ohm
(50ohm term at SMA connector, probed by same scope probe) .

 What gives? If I open up the can, what am I looking to possibly
replace/eliminate? How to open it? It's soldered shut (2x2in case).

 I need a good low-noise 100MHz sine wave for my application so I'm
tempted to open this guy up and replace the output circuitry with something
more suitable.

Thanks in advance for any pointers/info on these units!
-Logan
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