[time-nuts] more worm code
// worm: 32 diametral pitch (# of teeth per inch of diameter on pitch circle)
// 32 inch = 32/25.4 = 1.26 DP (in mm)
// nTeeth = DP * 2 * r;
// Create enveloping worm gear / pinion gear by incrementally
// subtracting off parts of the matching worm screw
// very slow to compute full gear with reasonable detail / smoothness
// 2014-08-19 J.Beale
//
// https://github.com/elmom/MCAD/blob/master/involute_gears.scad
//
https://github.com/syvwlch/Thingiverse-Projects/blob/master/Threaded%20Library/Thread_Library.scad
use MCAD/Thread_Library.scad
use MCAD/involute_gears.scad
eps = 0.05; // Epsilon = a small number
numberTeeth=40; // number of teeth on worm gear (pinion gear)
pitchRadius=40; // pitch radius of worm gear (pinion gear)
gearSegAngle = 10; // toothed part of gear segment (360 = full gear)
length=20; // length of worm screw
radius=10; // radius of worm screw
pi = 3.1415926535897932384626433832795;
pitch = 2*pi*pitchRadius/numberTeeth;
angle=360*$t;
offset=7.5;
distance=radius+pitchRadius+0.0*pitch;
GearThick = 10; // thickness of gear
xoff = -GearThick/2;
rAngle = 360/numberTeeth;
wAoff = -50; // initial angular offset of worm screw
// ===
// == QUALITY FACTOR (higher = slower, better) ==
// ===
cSteps = 17; // rotational carving steps for worm: larger = smoother surf.
StepsPerTurn = cSteps+3; // facets around worm screw: larger = smoother
// ===
EngageDepth = pitch*0.3; // carving out gear from blank
// echo(EngageDepth);
// worm(wA = 10);
module worm(wA = 0) {
translate([0,distance-EngageDepth,0.2-length/2])
rotate([0,0,180+wA])
trapezoidThread(
length=length, // axial length of the threaded rod
pitch=pitch, // axial distance from crest to crest
pitchRadius=radius, // radial distance from center to mid-profile
threadHeightToPitch=0.5, // ratio between the height of the profile and the
pitch
// std value for Acme or metric lead screw is 0.5
profileRatio=0.5, // ratio between the lengths of the raised part of the
profile and the pitch
// std value for Acme or metric lead screw is 0.5
threadAngle=14.5, // angle between the two faces of the thread
// std value for Acme is 29 or for metric lead screw is 30
RH=true, // true/false the thread winds clockwise looking along shaft,
i.e.follows the Right Hand Rule
clearance=0.0, // radial clearance, normalized to thread height
backlash=0.1, // axial clearance, normalized to pitch
stepsPerTurn=StepsPerTurn // number of slices to create per turn
);
} // end module worm()
module myToothBlank() {
translate([-GearThick/2,pitchRadius-8,0])
rotate([360/(numberTeeth*2),0,0])
cube([GearThick,pitch*1.5,pitch]);
}
module oneTooth() {
difference() {
myToothBlank(); // blank to form tooth via CSG subtraction
worm(wA = wAoff); // worm screw
for(f = [-.1:(1.0/cSteps):1.1]) { // computational machining (gear hobbing)
rotate([rAngle*f,0,0]) worm(wA = (360*f)+wAoff);
}
}
} // end module oneTooth()
// full gear = oneTooth * numberTeeth
// deg = 360.0/numberTeeth;
module gearSegment(segAngle = 90) {
for(deg = [0:360.0/numberTeeth:segAngle]) {
rotate([deg,0,0]) oneTooth();
}
}
module hub(ID = 5) {
difference() {
rotate([0,90,0]) translate([0,0,-GearThick/2])
cylinder(r=pitchRadius-(radius/2),h=GearThick,$fn=60);
rotate([0,90,0]) translate([0,0,-eps-GearThick/2])
cylinder(r=ID/2,h=GearThick+2*eps,$fn=20);
}
}
gearSegment(segAngle=gearSegAngle); // full gear = segmentAngle = 360
hub(ID = 8); // inner part of gear wheel with ID boresize
// worm();
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[time-nuts] cheap GPS receiver (NavSpark) with timestamp feature
It seems there is some interest in an inexpensive GPS receiver with a timestamp feature. As far as I know, the recently released NavSpark ( http://navspark.mybigcommerce.com/ ) may be the least expensive such device available. It was a crowd-funded effort from an established small GNSS design house in Taiwan (Skytraq). Recently I received some of the first of these items. It is programmable using a modified Arduino type development environment, and uses a 32-bit CPU (LEON3 Sparc-V8) for baseband processing with a 3rd party L1 receiver section (Skyworks SE4150L). The 1PPS output signal has a granularity of 10 ns, but the input signal timestamp feature is ~60 ns (GPS model with 16.368MHz clock) or ~40 ns (GPS + GLONASS model with 24.552MHz clock). I only just tested the demo timestamp code on a GPS model this morning, and it works mostly as expected, generating timestamps (text output on one of two UARTS) based on 1PPS input from a not-calibrated OCXO I had lying around. At least the millisecond output has jumps of ~ 60 ns size. The GPS time-of-day conversion seems to have a roundoff problem at the microsecond level. The NavSpark contains a TCXO of unknown performance, but with the entire unit costing $22 at retail, it's not gold- plated. 484282681.511417 ms, week #1794 since 1980; 2014-05-30 @ 02:31:06(+0.68151140) PM 484283681.511432 ms, week #1794 since 1980; 2014-05-30 @ 02:31:07(+0.68151140) PM 484284681.511452 ms, week #1794 since 1980; 2014-05-30 @ 02:31:08(+0.68151093) PM 484285681.511488 ms, week #1794 since 1980; 2014-05-30 @ 02:31:09(+0.68151093) PM 484286681.511498 ms, week #1794 since 1980; 2014-05-30 @ 02:31:10(+0.68151093) PM 484287681.511514 ms, week #1794 since 1980; 2014-05-30 @ 02:31:11(+0.68151093) PM 484288681.511524 ms, week #1794 since 1980; 2014-05-30 @ 02:31:12(+0.68151188) PM 484289681.511536 ms, week #1794 since 1980; 2014-05-30 @ 02:31:13(+0.68151188) PM 484290681.511541 ms, week #1794 since 1980; 2014-05-30 @ 02:31:14(+0.68151188) PM 484291681.511554 ms, week #1794 since 1980; 2014-05-30 @ 02:31:15(+0.68151188) PM 484292681.511570 ms, week #1794 since 1980; 2014-05-30 @ 02:31:16(+0.68151093) PM 484293681.511578 ms, week #1794 since 1980; 2014-05-30 @ 02:31:17(+0.68151093) PM 484294681.511538 ms, week #1794 since 1980; 2014-05-30 @ 02:31:18(+0.68151093) PM 484295681.511564 ms, week #1794 since 1980; 2014-05-30 @ 02:31:19(+0.68151093) PM 484296681.511588 ms, week #1794 since 1980; 2014-05-30 @ 02:31:20(+0.68151093) PM --- John Beale www.bealecorner.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] How I got my FE-5680A to lock in Sydney, Australia
The entry in the FE5680 FAQ on this subject may be helpful, if you haven't tried it already. http://ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5680a_faq#what_if_my_5680a_output_does_not_lock_up_after_several_minutes I have 3 of those units; one did not lock until I adjusted the trim-cap C217 to bring the free-running frequency of the oscillator into range. If you have a reasonably accurate counter you can check if this is the problem or not by seeing if the output frequency (which ramps up and down prior to lock) crosses through 10.00 MHz or not. Mine did not. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] NavSpark cheap Arduino-compatible with GPS builtin has timestamp feature now
The NavSpark project on Indiegogo has been mentioned here already, but I just wanted to note that (apparently at my request) today they announced the design was modified to include a timestamp function on external trigger input. Oliver Huang / SkyTraq: For NavSpark time accuracy is ~60nsec due to 16.368MHz clock. For -GL, -BD, time accuracy is ~40nsec due to 24.552MHz clock. http://www.indiegogo.com/projects/navspark-arduino-compatible-with-gps-gnss-receiver/x/6094574?c=comments I think he means granularity or precision, and not absolute accuracy. The true time-nut may not have a use for 40 or 60 nsec precision, but for a 32-bit Arduino-compatible with built-in GPS receiver and GPS-referenced timestamp, complete system including antenna, shipped, for $19 (GPS only) or $22 (GPS + Glonass) I think it is one of the better values I have seen. It is probably the cheapest way to measure long-term drift of an OCXO, and the programmability means it might be the easiest building block to use if you want to build your own GPSDO. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] talking to Synergy Systems SSR-6Tr (u-blox LEA-6T-0)
I was happy to find the one-off $35 deal for the SSR-6Tr from Synergy Systems is still on, and I got mine yesterday. It works OK using Motorola WinOncore12 to talk with it, in Motorola Binary format, and the performance does seem better than the Oncore M12+ I was previously using (eg. smaller average sigma on Lat/Lon/Height values from the same fixed antenna). The one datasheet I could find (nothing on the mfr's website!?) says this part can talk in three different formats including UBX Binary: P/N 16062133G SSR-6Tr ROM based, w/PIC, Mot Bin, UBX Bin, NMEA, No Battery I think several people on the list have this device, I'm curious how you interface with it. What commands switch to NMEA or UBX Binary? I tried to use ublox U-Center v8.1 without success (although that program works fine in generic NMEA mode on a different model GPS). Thanks for any advice! -John Beale n8juf ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] talking to Synergy Systems SSR-6Tr (u-blox LEA-6T-0)
FYI: I got an email reply from Art Sepin at Synergy with several helpful documents, which he did not post himself on time-nuts out of concern for seeming too commercial. Apparently they will go up on the Synergy website for the official launch of the SSR product line this June. But trusting that it isn't actually a secret, the magic command is @@Wb 0x01 0x34 --- For SSR boards that include the PIC processor, the @@Wb command has been included to switch between Motorola 9600 baud binary mode and native u-Blox binary NMEA modes. Because the PIC versions of the SSR boards are designed to plug into an M12+ or M12M slot, full functionality in u-Blox mode is available using u-Center but only at 9600 baud. For higher I/O speeds, select a u-Blox only SSR board part number. 1. For direct SSR interface to a microprocessor, use the following: The Hex command is 40 40 57 62 01 34 00 0D 0A (@@Wb0134CRLF). This functionality is available in the full and the evaluation copy of SynTAC available here: http://www.synergy-gps.com/index.php?option=com_contenttask=viewid=185Itemid=196 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] would an optical primary standard provide any general benefit?
Having read this NIST review paper by Thomas E. Parker, The uncertainty in the realization and dissemination of the SI second from a systems point of view http://tf.boulder.nist.gov/general/pdf/2564.pdf ...it seems that any potential improvement in frequency standards (Cs fountain - optical clocks) will not benefit most time/frequency users, because existing long-range time-transfer methods (TWSTFT and GPS carrier phase) are still limited to at best 2E-16 for 30-day averaging, and there is no generally practical way to improve them currently in sight. (Laser ranging of satellites being considered not generally practical). Just curious what people think, is this too pessimistic a view, or is it fair to say that having a 10x improved primary standard would not improve stability or accuracy for anyone outside of stabilized optical-fiber distance from such a standard? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] DTV tuner chip usable for GPS front end?
I suppose there is limited interest in homebrew GPS receivers given how cheap the fully integrated chipsets are. However, just noticed the below tuner chip intended for DTV, actually lists GPS L1 as an applicable frequency. A TV Tuner USB stick using this chip is available for $20, and some SDR type software is apparently working with it: http://sdr.osmocom.org/trac/wiki/rtl-sdr Has anyone here played with this device? from http://www.elonics.com/product.do?id=1 The E4000 is a highly integrated multi band RF tuner IC implemented in CMOS, ideal for low power digital terrestrial TV and radio broadcast receiver solutions. The E4000 contains a single input LNA with RF filter, whose centre frequency can be programmed over the complete frequency range from 64MHz to 1700MHz. Broadcast Standards DVB-T (174-240MHz, 470-854MHz) ISDB-T (470-862MHz) DVB-H (470-854MHz, 1672-1678MHz) CMMB (470-862MHz) D-TMB (470-862MHz) T-DMB (174-240MHz, 1452-1492MHz) DAB (174-240MHz, 1452-1492MHz) MediaFLO (470-862, 1452-1492MHz) GPS L1 band (1575MHz) [...] ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 5680A what is a reasonable case temp ?
From: Chris Albertson albertson.ch...@gmail.com I'm ready to mount on of my 5680A in a case and looking for suggestions on what one would consider a reasonable maximum case temp. With the FE-5680A mounted to a 4x6x1 finned aluminum heatsink as shown here: https://picasaweb.google.com/109928236040342205185/FE5680A#5685636673930493138 the opposite side of the case reaches 55 C in a 20 C ambient, with no fan whatsoever. Running a 40mm 12V fan at 5V aimed at the heatsink drops that to 45 C. At 5V the fan is nearly silent, and the airflow is quite weak. Despite the internal temperature compensation via DDS offset updates that the unit apparently does, I measured one of my units to have a 7E-12 per degree C temperature sensitivity, larger than I expected. So I do want to use a thermostat on the fan. The Symmetricom XPRO manual http://www.symmetricom.com/link.cfm?lid=7082 (which I believe is a somewhat similar Rb design) estimates that the lifetime of that unit doubles when baseplate temperature is reduced from 60 C to 40 C (MTBF: 243k hours = 591k hours). Note that 243k hours is about 28 years. On the other hand, my assumption is these surplus FE-5680A units were cheap because they were considered end-of-life already. Maybe for something somewhat fixable, like the 60 MHz VCXO center frequency having drifted out of a spec window. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Portable Digital 'scope (actual BW: 2 MHz)
For what it's worth: The DSO203 is good to about 1 MHz to 2 MHz, after that signals get very rounded. This is caused by the analog path, not by the digital sample rate. http://forums.parallax.com/showthread.php?127201-New-%28DSO203%29-portable-oscilloscope!/page2 ---Original Message--- From: Rob Kimberley robkimber...@btinternet.com To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com Subject: [time-nuts] OT - Portable Digital 'scope Sent: 23 Feb '12 12:01 I'm looking at Item: 300658066641 on EBay, and wanted to know if anyone in the group had any experience of this product. I know this is way off topic, but as a group it's nice to know what's out there and possibly useful in our mutual hobby. Thanks for reading. Rob Kimberley ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Schematic capture: KiCad?
In case you haven't already had enough suggestions: KiCad is an open-source option. It is much less popular/well known than Eagle, but it is free, has no* limitations on layers, parts, or board size. Runs on Linux and Windows. All design files are in plain text format, hence easy to parse by eye or other tools as desired. There is some learning curve, as with all CAD tools. I laid out this simple decade divider PCB using KiCad: http://bealecorner.com/pcb/dd1/ and it wasn't too bad. It has an active user's group list. http://tech.groups.yahoo.com/group/kicad-users/ - user's group mailing list http://kicad.sourceforge.net/wiki/Main_Page - main project page http://teholabs.com/knowledge/kicad.html - tutorial http://www.youtube.com/watch?v=rkQ0nVX1q1k - video tutorial *actually, a maximum of 16 layers, and 44 x 44 inches in size. *Usually* that is not a limitation :-) Like others here, I recommend against free single-vendor lock-in tools that won't give you Gerber output and easy design portability. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Rubidium Performance: DDS noise effect on 10 MHz
From: John Miles jmi...@pop.net So far, the FE-5680A is doing well in the ADEV department, but its AD9832 DDS chip adds some substantial noise and spurs to the 10 MHz output. [...] The overall SSB C/N ratio I'm seeing between 1 Hz - 100 kHz is pretty much in line with Analog Devices' data sheet, as are the spur levels. In the current 5680A units, the 10 MHz output comes from the 60 MHz VCXO (divided by 6 in CPLD) and not direct from a DDS. If my architecture understanding is right, the DDS signal output is mixed with the VCXO output only at the 114th harmonic of 60 MHz, and it's the PLL (looking at the optical signal from the Rb) that drives the VCXO to keep it lined up. As I understand it, DDS phase noise should be divided by a factor of 6*114 by the time it appears at the 10 MHz output, and at larger frequency offsets the amplitude should also be (significantly) reduced by the PLL loop filter. I don't have any phase noise measurement tools myself, so this is just an academic argument, but if there is significantly more noise on the 10 MHz than expected for a 60 MHz VCXO, I wonder if it's just inadequate filtering of an internal power rail. Is the unit under test being driven by a linear, or switching supply? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FE5680 missing PPS - hallelujah!
Thank you Bob! I just tried removing the lock indicator LED on my three 5680A units and sure enough, in every case, there was the 1 PPS (+5V, 1 usec, rise/fall time ~100 ns) just as if it had always been there. As a reminder, this and much else useful lore is now collected at the ongoing FE-5680 FAQ at http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5680a_faq (and if the answer to any of your nagging FE-5680A questions is missing from the FAQ, please feel free to add it!) -John On 2/2/2012 12:46 PM, bob grant wrote: Some info... Its tempting to attach an LED to the /LOCK signal on the DB9. However this signal is very weak and the LED does not seem very bright and PPS signal does not pulse...Hmm Internally the /LOCK pin is connected the 74AC240 buffer, but with an LED helping to keep the signal voltage high (2.3V) a logic low is never asserted. This logic low is needed to enable one half of the 74AC240 buffer (pin 1) that gates the PPS signal. Don't directly drive LEDs from the LOCK signal on the DB9 and, voila, the PPS signal reappears. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FE-5680A programming connector pinout
http://www.rhodiatoce.com/pics/time-nuts/FE-5680A_annotated.jpg Excellent work! I look forward to any further info. Great picture with the pins and some parts labelled. By the way, if you want you could add the frequencies going into and out of the Xilinx XC9572XL CPLD part: Pin 64: 60 MHz in from VCXO Pin 1: 20 MHz out to AD9832 DDS chip Pin 22: 30 MHz out Pin 49: 10 MHz out to sine shaping network See also: https://plus.google.com/photos/109928236040342205185/albums/5680473650837554113/5685304134718133138 It might clarify things to point out the 60 MHz through-hole crystal pins visible immediately below the MMBV432 varactor diode. Knowing that's the varactor, and looking at the circuit I'm guessing the VCXO tuning voltage must pass through the 10K resistor next to mini-coax connector J8 (then past the bypass cap, through the 1.0 uH inductor, to the diode). That 10k connects through a 1k to pin 8 (output 3) of the TLC27M4B quad opamp on the other side of the board, near the 60 MHz xtal. Hmm sure enough: at startup, pin 8 swings between 0 and 11.9V, before the unit locks, which in my case happens at 7.3 Volts. (The opamp is powered from a 13.16V supply, output swings typ. 1.3V below the + rail.) Just for fun, here's a plot of the VCXO tuning voltage at startup: https://picasaweb.google.com/109928236040342205185/FE5680A#5704421825887557874 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GHz output from fe5680a
What would you intend to do with the signal? I'm not a microwave expert, but I believe the only microwave signals in the FE-5680A are the output of the step-recovery diode that multiplies the 60 MHz VCXO signal up to the 114th harmonic, plus that mixed with the 5.313 MHz DDS output to reach the Rb frequency. ( 114 * 60 Mhz - 5.313 Mhz - 6.835 Ghz) The SRD output would be just a mix of a lot of harmonics, not any sort of clean signal; I suspect the only real filter is the resonant cavity which is occupied by the Rb bulb. I suppose a small enough probe into that cavity might not detune it too much, but you'd probably need an additional amplifier to do anything with that signal. Iin this device the Rb vapor itself does not generate microwaves (like an active H maser), it just absorbs them, and it changes optically if the signal happens to be at the resonance frequency around 6.8 GHz. ---Original Message--- From: chris 0 viscousplac...@gmail.com Subject: [time-nuts] GHz output from fe5680a I'm just wondering if its possible to tap into the GHz output from the rubidium in the fe5680a. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FE-5680A decoded - another piece of the puzzle
On 1/29/2012 8:22 PM, Skip Withrow wrote: I recall someone implementing C-field control on a FE-5680A with the pot disabled, but cannot find it now. If someone can point me to that post I sure would appreciate it. I added that post to the FE-5680A FAQ, and added my own photo also to help locate the part. Note, I have not actually tried this modification myself. http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5680a_faq#adding_an_analog_adjustment_pot Original post was by Bill Riches, Thu, 22 Dec 2011 14:01:18 -0800 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] FE-5680A command decoding speculation
Speculation... just for fun. Seeing Javier's great recent work on the 5680 DDS operation has me thinking more about two of the mystery commands. If the unit is applying a periodic correction to the DDS frequency beyond what the user requests via RS-232 commands, as a function of (for example) temperature, and/or a power supply voltage, it would need some calibration coefficient. Those correction factors would logically be a user-settable parameter. We know there is a 12-bit 4 channel A/D chip onboard, apparently monitoring temperature (and supply voltage?) and maybe that's not just a passive monitor function, but used to generate the correction factor. Now, looking at the response to Cmd 0x57 and 0x59 on my unit, I see a long string of bytes which look like sets of 2-byte pairs, the second byte of each pair differs by roughly the same number from the previous. Each unit has a different number of these pairs, and they are followed by all 0x00 bytes. Pure speculation here, but if the unit was keeping a log of the most recent commanded voltage or temperature coefficient correction factors, and this was done at regular intervals, it might look a lot like that. Another possibility is an automatically generated correction, if there is any known drift with time (?). Yet another possibility is a look-up table, for example, to take the measured temperature to find the right DDS offset correction factor. I might expect the lookup table to be a consistent size, though. In case of interest, below is the data I'm talking about, from my three units. Remember the first 4 reply bytes is a command header, and the last byte is a checksum. FE-5680A Unit Number 62388: -- Cmd 0x57 0x56 byte reply: 57 56 00 01 30 40 00 4B 00 58 00 63 00 6E 00 7A 00 85 00 90 00 97 00 9C 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0A Cmd 0x59 0x56 byte reply: 59 56 00 0F 30 BF 00 A2 00 80 00 2F 00 00 00 EA FF 9E FF 7C FF 4A FF 39 FF 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 06 FE-5680A Unit Number 66721: -- Cmd 0x57 0x56 byte reply: 57 56 00 01 50 41 00 43 00 47 00 4A 00 4E 00 51 00 55 00 58 00 5C 00 5F 00 63 00 66 00 6A 00 6E 00 71 00 75 00 78 00 7B 00 7F 00 82 00 85 00 89 00 8C 00 90 00 93 00 97 00 9A 00 9E 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 A5 Cmd 0x59 0x56 byte reply: 59 56 00 0F 50 CB FF BC FF C6 FF B0 FF B5 FF A9 FF 8E FF 77 FF 9B FF B0 FF 8C FF CD FF E5 FF 00 00 81 FF B0 FF C1 FF D6 FF DD FF D2 FF D9 FF B7 FF D8 FF CB FF E4 FF DB FF F9 FF E1 FF 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 B7 FE-5680A Unit Number 72476: -- Cmd 0x57 0x56 byte reply: 57 56 00 01 68 3F 00 42 00 46 00 4A 00 4D 00 51 00 55 00 58 00 5C 00 5F 00 63 00 66 00 6A 00 6D 00 71 00 74 00 78 00 7B 00 7F 00 82 00 86 00 89 00 8D 00 90 00 94 00 97 00 9B 00 9E 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 E6 Cmd 0x59 0x56 byte reply: 59 56 00 0F 68 FF FF 01 00 E3 FF CE FF D8 FF EA FF D2 FF F0 FF FE FF 16 00 0A 00 0D 00 F6 FF 00 00 EF FF FE FF DD FF D3 FF E2 FF F5 FF F2 FF F3 FF E5 FF EE FF B3 FF C4 FF DA FF A9 FF 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 4B --- John Beale n8juf ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] FE-5680A FAQ update: question about frequency synthesizer architecture
I added a bit to the electronics section of the FE-5680A FAQ as below. http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5680a_faq#electronic (Note- until today, I had the 8 and 6 digits transposed, calling it the fe5860a. But no one noticed :-) The updated section is below. I measured the 20 MHz input and 5.3 MHz output of the DDS, but I'm puzzled by how the tuning resolution (4.6 mHz) of the DDS output is divided by such a large factor to achieve 0.18 uHz resolution at the final 10 MHz output. Can any frequency synthesizer gurus explain how this is done? - The main digital electronic parts are: Maxim DS80C323END (8051, 44TQFP, -40/+85C, 18 MHz, 4 8-bit ports, 64K/64K ROM/RAM ) STMicro PSD813F1V-20UI (1Mbit flash, 256Kbit EEPROM, 16Kbit SRAM, 3k PLD gates, ISP) Xilinx XC9572XL VQ64BN (64-pin CPLD, 178 MHz, 72 macrocells) Analog Devices AD9832BRU (25 MHz Direct Digital Synthesizer, on-chip 10-bit DAC) Other ICs on digital side of PCB: Maxim MAX708 CPU supervisor Maxim DS1832 CPU watchdog, brownout detect Maxim MAX882 3.3V LDO (5V input) Maxim MAX1246 4 ch. 12-bit ADC Maxim MAX3232 RS-232 transciever Operation A 60 MHz sine from the VCXO enters CPLD pin 64 and it generates 3.3V square wave outputs at 30 MHz (pin 22), 20 MHz (pin 1), and 10 MHz (pin 49). The 20 MHz output goes to the clock input of the AD9832 DDS chip, which generates a 5.3 MHz sinewave output (nominal, when the RS-232 offset is set to 0). The frequency resolution of the DDS itself is (Fclock)/2^32 and since Fclock=20 MHz, the 5.3 MHz output is tuned in steps of 4.657E-3 Hz. However, the FE-5860A 10 MHz output step size is 1.7854E-7 Hz, so the DDS output frequency must be effectively divided in the overall system by a factor of about 26000 at the 10 MHz output (or a factor of 4333 at the 60 MHz VCXO frequency). The Rb hyperfine transition is at 6.835 GHz which is about 683x larger than 10 MHz. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FE-5680A FAQ update: question about frequency synthesizer architecture
I appreciate those notes; the data sheet for the DDS part also explains it. It has a 12-bit LUT driving an internal 10-bit DAC (the 5.3 MHz sine is still a bit coarse, with 4 samples per cycle, but in the 5680 it is cleaned up by an external filter). Because phase information maps directly into amplitude, a ROM LUT converts the phase information into amplitude. To do this, the digital phase information is used to address a sine ROM LUT. Although the NCO contains a 32-bit phase accumulator, the output of the NCO is truncated to 12 bits. Using the full resolution of the phase accumulator is impractical and unnecessary because this would require a look-up table of 2^32 entries. ...from http://www.analog.com/static/imported-files/data_sheets/AD9832.pdf However, my question was actually about how the remainder of the circuitry in the FE-5680A combines the 5.3 MHz from the DDS (at 4 mHz tuning step size), and the 60 MHz VCXO, to reference against the 6.835 GHz Rb frequency and ultimately achieve 0.18 uHz (micro-Hz) tuning step size at the final 10 MHz output. I don't think a simple multiplier-mixer-divider chain (for example) could give you such a small tuning step size at the output, the frequency ratios don't work out. I've heard of fractional-N PLL synthesizers but I'm not sure if that's the principle here. ---Original Message--- From: Graham / KE9H time...@austin.rr.com The AD9832 is an Analog Devices DDS which has a 32 bit tuning word. The way a DDS generates the output, is that it (effectively) has a cosine wave look-up table, with 2^32 entries that comprise a single cosine wave cycle. The tuning word tells it how many entries the DDS should advance every reference input clock cycle, then it pushes that amplitude value in the look-up table to the output D-A converter. So, if the input reference is 20 MHz, then the DDS can generate frequencies with a resolution step of Vref/2^32 = 20,000,000 / 4,294,967,296 = 0.0046566 Hz. The DDS output frequency is(tuning word /2^32) times Vref. In the actual implementation, rather than a 4 billion entry look-up table, I am sure they have some algorithm that calculates the amplitude of a cosine wave, or a much smaller table with a sophisticated interpolation routine. --- Graham / KE9H ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Determination of the placement of the first pps (FE-5680A)
Yikes, please delete that pastebin link. That was just my initial try at a FAQ. A significantly updated and more current version of the FE-5680A FAQ is located at http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5860a_faq Scott's utility seems to be able to dump the FEI unit serial number, and perhaps the included options. If my guess is correct, all three of the units I have are equipped only with Option 2 which is the RS-232 port. But there are many possible varieties of 5680 units out there, and some of them may have the 1 PPS behavior you mention while others do not- I have no information on that. ---Original Message--- From: Magnus Danielson mag...@rubidium.dyndns.org Didn't see these link hit the list: http://pastebin.com/S8UcnCMZ http://www.dd1us.de/Downloads/precise%20reference%20frequency%20rev%200_7.pdf http://vk2xv.djirra.com/tech_rubidium.htm ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FE-5680A FAQ now at www.k04bb.com wiki
I put my start at a FE-5860A FAQ on the K04BB wiki page here: http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5860a_faq The wiki is open (amazing I didn't see any spam there) so anyone can add their own FE5860 info as well. Thanks Didier for your very useful page! ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] VCXO center frequency offset
Yes... if the C217 trimmer was not already at the very minimum setting! I was thinking of possibly removing it altogether, maybe adding back a smaller fixed C. All three of my units are pretty low in VCXO center frequency, and in fact I wonder if that's the reason they were on the surplus market in the first place. ---Original Message--- From: Bob Camp li...@rtty.us Based on the frequency plot of your unit, it swings about 35 Hz high and about 170 Hz low as it sweeps. You could bump the trimmer on the VCXO and move it up by about 70 Hz or so to keep it from running out of range. Since the VCXO is trending down in frequency as it warms up, this may be needed sooner rather than later ... -Original Message- Great detective work Scott! I'll bet Channel 4 is voltage to the VCXO. It is driven up and down at startup searching for the lock, then it settles down, but the oscillator components are also affected by temperature so the VCO voltage would logically track the temperature too. At least it seems a reasonable theory. For example, look at this plot of the 10 MHz output frequency after powerup. It has a similar look to your Channel 4, except for the post-lock drift. https://plus.google.com/photos/109928236040342205185/albums/5680473650837554 113/5681715799377076466?banner=pwa -John Beale ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] FE-5680A FAQ (Frequently Asked Questions)
I don't know if I'm volunteering for this, but here's a start of a 5680A FAQ list anyway. A lot more could be added. http://pastebin.com/rZhySgAK I agree that a FAQ would be handy to have this on a permanent webpage, which might cut down on some list traffic covering old ground. ---Original Message--- From: ewkeh...@aol.com To: time-nuts@febo.com Subject: Re: [time-nuts] 15 volt power supply for FE-5680A on eBay Sent: 19 Jan '12 03:34 Pete Thank you this is valuable info. I noticed that an effort is underway to centralize info on the 5680. Would be nice if some one with time and software expertize would combine all the information. I cut and paste what ever I find on the list and will be glad to forward it to a volunteer. This kind of findings should be included. Bert Kehren ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FE-5680A Voltage tolerance
Very interesting data. I wonder if this has to do with the nominal center frequency of the internal 60 MHz VCXO (which is divided by 6 to generate the 10 MHz output). On my units, the center frequency is pretty low and the 10 MHz output is near the top of the range (actually beyond the range on one unit, so it would never lock, until I tweaked the C217 trimmer). If there's an internal supply rail that sags even slightly, that would probably put at least one of my units out of lock range. Of course there's more to the whole system, maybe the Rb doesn't reach temperature, or the microwave section droops or has inadequate power level, etc. I'd suspect even if the unit does work at very low voltages, it is more marginal, noisy and less stable. It is surprising that it works at all below 11 V input, though. -John Beale From: gonzo . cadbl...@hotmail.com Subject: [time-nuts] FE-5680A Voltage tolerance Experiment for the day. I thought I'd follow Dons quote and see how tolerant my unit is. My benchmark is at 15.5V it locks in about 3min. I backed off the supply to 10.8V and the lock time (from cold) is 8min. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Progress on the FE-5680A serial commands!
On 1/19/2012 9:52 PM, Scott Newell wrote: http://n5tnl.com/time/fe-5680a/graphs/fe5680_2_ch3.png http://n5tnl.com/time/fe-5680a/graphs/fe5680_2_ch4.png This assumes that the reply from the undoc command 0x5a is the raw counts from the 4 channel 12 bit ADC. I think channel 3 is a temp sensor. What would channel 4 be? Photodiode output? Great detective work Scott! I'll bet Channel 4 is voltage to the VCXO. It is driven up and down at startup searching for the lock, then it settles down, but the oscillator components are also affected by temperature so the VCO voltage would logically track the temperature too. At least it seems a reasonable theory. For example, look at this plot of the 10 MHz output frequency after powerup. It has a similar look to your Channel 4, except for the post-lock drift. https://plus.google.com/photos/109928236040342205185/albums/5680473650837554113/5681715799377076466?banner=pwa -John Beale ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] FE-5680A Frequently Asked Questions
Here are a few links to get you started in your quest for more info about the FE-5680A FE-5680A Notes, links, and control software: http://www.vk3um.com/Rubidium%20Standard.html Further Information on Rubidium Std. FE-5680A http://www.vk3um.com/Fe-5680A4.pdf FE-5680A Technical Manual http://www.wa6vhs.com/Test%20equipment/FREQUENCY%20STANDARDS/FE-5680A/5680%20TECH%20MANUAL.pdf OEM website product page http://www.freqelec.com/rb_osc_fe5680a.html A few misc. photos of my own: https://plus.google.com/photos/109928236040342205185/albums/5680473650837554113 ---Original Message--- From: Robert Benward rbenw...@verizon.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] FE-5680A adjustment screw? Sent: 18 Jan '12 12:51 I am sure some has covered this already, but does anyone know where I can get software or a command set to tweak the unit? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] cheap USB voltage sensor
Bringing up a question: Does anyone know of a cheap ($20ish) USB voltage sensor (16 bits or better, ideally).. I can see one of those Atmel USB capable micros (like the one on the Arduino Uno) hooked to a dual slope or successive approximation ADC. Doesn't quite meet your price, but there's a 3.3V version of an Arduino called a JeeNode designed for sensor work, and there are a number of I2C based sensor plugins for it. For example the analog plug based on Microchip MCP3424 with 4 channels of differential inputs at 18 bits. Jeenode (kit) is $23 and Analog plug (assembled) is $12. It's the standard Arduino architecture, so it is simple to use and (re-)program from your PC via USB, no extra programmer needed. http://shop.moderndevice.com/products/jeenode-kit http://shop.moderndevice.com/products/jeelabs-analog-plug I have some and they work well. Here's a plot of voltage vs time on an AA battery, showing the 18 bit performance (1 LSB = 15 uV). Noise is generally +/-1 LSB. https://picasaweb.google.com/lh/photo/q7Lq4oAX_0347S8BO0eHSA You can plug up to four analog plugs directly into the JeeNode (software I2C) and these can actually be daisy-chained as well, with 6 different I2C addresses per I2C chain, for up to 24 total plugs per JeeNode which would be 96 ADC channels. If you are in Europe you can buy hardware direct from the designer at http://jeelabs.com/ ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FE-5680A PPS on pin 6 (or not)
All three of my FE-5680A units show a constant DC voltage on pin 6, with absolutely no PPS signal. This is when pin 3 is low (lock) and the 10 MHz output is indeed locked at 10 MHz (within 4E-10 anyway). I am using a Tek TDS-210 digital scope which certainly has no problem with a 1 usec pulse, and in fact, I did see a nice square 1 usec pulse on Pin 6 once, from one unit. But it went away after a power cycle, and did not return. I know many (most?) people do see the 1 PPS so perhaps all three of my units are damaged (?) I presume the 1 PPS signal would come from the XC9572 CPLD which also drives the 10 MHz signal, so I'll try tracing back which pin that is. I labelled a few CPLD pins already (60 MHz in, 30 MHz and 10 MHz out) here: https://picasaweb.google.com/lh/photo/dUtTwuNnP-y2nL-wR84ELNMTjNZETYmyPJy0liipFm0 ---Original Message--- From: Chris Albertson albertson.ch...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] FE-5680A arrived Sent: 11 Jan '12 08:37 On Tue, Jan 10, 2012 at 10:11 PM, Joseph Gray jg...@zianet.com wrote: I'm not seeing a PPS on either of these. All I see is about 17 mV P-P of noise that looks like a multi-stepped sine wave. I'm using a TDS 340 scope. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FE-5680A performance - 1 PPS output issue
I think there is something funny about the 1 PPS output on pin 6 from the currently available cheap FE-5680A units. I have three of these units. On one unit, on one occasion, I did observe a logic-level 1 PPS pulse, exactly 1 microsecond wide. But after a power cycle it never came back, although the unit indicates a locked condition, and is apparently working. The other two units also seem to work (10 MHz output OK, lock OK) but I have never seen a 1 PPS signal on pin 6 from them. My Tek TDS-210 is easily capable of triggering on and displaying a 1 usec pulse. Is it possible the pulse appears only after a RS-232 command, or after some other special condition? ---Original Message--- From: David davidwh...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] FE-5680A performance Sent: 05 Jan '12 07:49 On Thu, 05 Jan 2012 01:44:13 -0800, Hal Murray hmur...@megapathdsl.net wrote: albertson.ch...@gmail.com said: Have an older Tek 465 scope that is in only fair shape and I see nothing on that pin but milivolt level sine wave of about 60MHz. I can't set the scope to show any hint of a PPS ... I do have a 465. You should be able to see a 1 uSec PPS. 60MHz is about a 6nS rise time and is easily fast enough to see it. Now turn up the Intensity until you can see the pulse. It might help to turn down the room lights. This is the problem. With a 1 second repetition rate, the brightness is going to be very low. The old ways of viewing such a low repetition rate signal include using a hood or dark room, special CRT phosphors, photographic film, MCP (micro channel plate) intensified CRTs, and of course analog storage and later digital storage. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FE-5680A performance - replacing fried chip
I did something similar- momentary contact of +15V supply with one of the other pins- might have been the +5 Vin, or another signal. The 75ACT240 became very hot. I ordered a replacement 75ACT240 part, swapped it in, and the unit seems to work fine now. Note this is the 0.3 wide device, DigiKey p/n 74ACT240SC-ND. Confusingly, that part in 20-pin SOIC is made in two different body widths: 0.209 / 5.3 mm and 0.295 / 7.5 mm. This photo shows the board with the smoked chip removed (U503 at upper left), before I installed the replacement https://picasaweb.google.com/lh/photo/mF9WSGlEQjA8MqHhbPOJRdMTjNZETYmyPJy0liipFm0?feat=directlink -john ---Original Message--- From: EB4APL eb4...@cembreros.jazztel.es To: time-nuts@febo.com Subject: Re: [time-nuts] FE-5680A performance Sent: 05 Jan '12 11:37 I found it, I used the +15 V of my triple output supply to power the pin 4, +5 V input. A 75ACT240 popped up and who knows the health of the other things. Wish me luck, Ignacio, EB4APL El 05/01/2012 18:54, EB4APL wrote: I agree, I've seen it in a Tek 7623A with the storage on, it is quite difficult without it. Regards, Ignacio, EB4APL PD. Just trying to verify this I made some error and let the magic smoke leave the unit. It is still smelling ... ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FE 5680a 3pay 36.89 includes shipping. Finally ordered one
On 1/3/2012 8:20 AM, Robert Benward wrote: I got mine for around $25 in a regular bidding affair. Mine had trouble locking, It only locked a handful of times, and that took forever, but most of the time it just sat there and cooked. The seller replaced it and the new locks up in 2 or 3 minutes. I did not have to ship the old one back. The Lock output signal doesn't seem to have enough drive to turn on an LED. One of the three FE-5680A units I got behaved exactly that way. Turns out some part of a VCXO circuit had drifted over time (I assume) so the free-running frequency never quite reached up to 10.000 MHz enabling lock to the signal from the physics package. Assuming you do have a 10 MHz output signal, put a counter on it while it is warming up and look at the frequency. After I fixed it, the frequency vs time from startup plot looked like this: https://picasaweb.google.com/lh/photo/7E22rkh_YivyesrnTog6atMTjNZETYmyPJy0liipFm0?feat=directlink The fix was to take off case top and bottom and tweak the trimmer cap marked C217 slightly, it is near Y200 (crystal with round PTC thermistor attached). Here's a photo of that part of the board: https://picasaweb.google.com/109928236040342205185/FE5680A?authkey=djqVhWs9LkM#5680683008490223330 Of course there may be some completely different problem with your unit, but it's something to try, if you want to open it up and play with it. -John Beale ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] crunching numbers from XOR phase detector
Previously I have been comparing 10 MHz frequencies using TvB's picPET device plus a picDIV divider to get a 1 PPS signal, but I wanted more resolution for comparing relative drift of two Rb references. I got square wave outputs from my references (see my previous posts) and I made a simple XOR phase detector from a single XOR gate (74LVC1G86) : https://picasaweb.google.com/lh/photo/ofFwP8Eo1qFAzNObq69iCtMTjNZETYmyPJy0liipFm0 I have read about how nonlinear the XOR PD becomes at the endpoints (0 and 180 phase shift) although this one seems to work pretty well, and the output looks reasonably triangular: https://picasaweb.google.com/lh/photo/swKVhhP7NerRvMKdnW8rjtMTjNZETYmyPJy0liipFm0 There is some nonlinearity but it seems consistent from cycle to cycle. I might be able to reduce the bumps with better circuit layout, shorter wires, terminated lines etc. But just for playing around with my initial data, I think I can model the shape of the response and get a more accurate reading of instantaneous phase angle vs time. I could write some code for this, but I suspect this wheel has been invented before... is there any reference I should consult? I think something similar is done inside the PIC-TIC to calibrate its response? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FE-5680A clock shaping (sine - square wave)
On Thu, 29 Dec 2011 21:14:30 -0800, John Beale be...@bealecorner.com wrote: In case it's useful... there are many ways to get a square wave out from a sine wave in, but one straightforward way is with a comparator. [...] FWIW, I decided on a more straightforward way to get a square wave output from my FE-5680A: bypass the internal sine-wave filter, and take the original 10 MHz output direct from the XC9572 CPLD ! (now, I vaguely recall, this may have already been described on the list...) Here's a photo of the modification I did: unsolder and rotate the 15 ohm resistor on CPLD pin 49, so it now feeds a short ribbon cable, which runs through the hole in the case intended for the (non-working) trim pot: https://picasaweb.google.com/lh/photo/YkQseTWUZolGYd5VSwE9odMTjNZETYmyPJy0liipFm0?feat=directlink What the square wave looks like coming out through the cable, on a TDS-210 with 10x probe, no termination load: https://picasaweb.google.com/lh/photo/lcFB0P5rEEd10K508nWCv9MTjNZETYmyPJy0liipFm0?feat=directlink I see a 10 MHz 3.3V square wave with ~5 ns risetime and about 0.3 Vpp of ringing, probably as good as I could expect with this scope and wiring arrangement. I suspect this way I will get better jitter performance than I could expect trying to square up the standard sine wave output by whatever means. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] FE-5680A clock shaping (sine - square wave)
In case it's useful... there are many ways to get a square wave out from a sine wave in, but one straightforward way is with a comparator. Some work better than others. The slow ones won't work at all at 10 MHz, and the very fast comparators (MAX999, ADCMP600, LT1116 etc.) are more expensive, and perhaps harder to work with. I tried a MAX9013 in SO-8 package and it works well for the job. You can see my schematic, circuit and scope plots at the bottom of this page: https://picasaweb.google.com/bealevideo/FE5680A My circuit works best with a sine wave input amplitude above 100 mVpp. Below that level, the duty cycle starts to become noticeably worse. I am using some hysteresis, but it may not be necessary. Previous to those pics on the page, you also see a circuit which did not work so well, using a MAR-1 (broadband DC-1GHz MMIC amp). It's intended as a linear amp, and it does not saturate in a symmetric way even with large input signals. Here are a few other circuits of interest, which I did not try: http://www.ko4bb.com/~bruce/CLKSHPR.html http://www.ko4bb.com/Timing/ClockShaper.php ...and by the way, my FE-5680A shows a consistent -7E-12 per degree C temperature sensitivity (measured at case temp 42 and 52 C). Has anyone else measured theirs? -john beale ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] FE-5680A temp coefficient seems to be -7E-12 per degree C
My measurements on one FE-5680A Rb sample indicate a temperature coefficient of -7E-12 per degree C (T measured at exterior case top center); more details below. Can anyone opine if this is a reasonable value? I can't say anything about long-term drift until I stabilize the case temperature. Currently experimenting with a variable-speed fan and PID controller looking at a thermistor attached to the case, to that end. The starting point of -3.2E-10 offset is just how the unit arrived, I have not yet tried changing the frequency via RS-232 commands. With a 40mm 12V fan running at 5V and pointed at a 4x6x1 finned heatsink the unit is mounted on, the case temp. drops 10 degrees (55C - 45C), and the unit 15Vdc power draw increases 2 watts. (Perhaps a bit less, I actually measured the power at 120Vac with a WattsUp Pro meter, but I assume my DVE 15V 2A switcher is pretty efficient. Supply is from lightobject.com and actually provides 14.84 V, but that seems to work.) Ambient room temp was also logged; it varies by about 2 C as building heater cycles. FE-5680A 10 MHz F_offset vs. GPS using picPET: http://www.leapsecond.com/pic/picpet.htm and Sure Electronics GPS: http://www.leapsecond.com/pages/MG1613S/ -- Foff = -3.20E-10 7:30 am Dec.14 2011 (32 hours). Case top: ~45 C Foff = -3.22E-10 9 pm Dec. 15 2011 (14.5 hours). Case top: 41.5-44.5 C Foff = -3.227E-10 3 pm Dec. 17 (40.9 hours). Case top: 42-44 C Foff = -3.216E-10 11 pm Dec. 19 (46.5 hours). Case top: 42-44 C Foff = -3.902E-10 10 am Dec 20 (11 hours). Case top: 52.5-53.5 C (fan off) Foff = -3.910E-10 10 am Dec. 21 (12 hours of data). Case top: 52.5-53.5 C conclusion: tempco is -7E-11 with +10 C, or about -7E-12 per degree C -- see also: https://picasaweb.google.com/109928236040342205185/FE5680A -- ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] FE-5680A internal signal waveforms (60, 30, 10 MHz)
I have two of the FE-5680A (FEI P/N 217400-30352-1) Rb references, and I'm looking at the signals on digital side of the PCB inside, in particular the Xilinx CPLD, that is the XC9572XL in a 64-pin package. Here is a photo with the signals marked: https://picasaweb.google.com/109928236040342205185/FE5680A#5685304134718133138 pin 64 has a nice looking 60.00 MHz sine wave, I gather this is the input signal to the CPLD. pin 22 has a 30 MHz square wave, although it has some ripples (see scope trace in same Picasa album) pin 49 has a 10 MHz square wave but with a very odd shape. Pin 49 is the signal which is LC filtered (?) to become the 10 MHz sine wave out on the internal J8 mini-connector, and the external DB9. The signal is about 3.3 Vpp, but becomes an 11 Vpp sine wave at the far side of a blue part (inductor?) marked 2R2J. The 10 MHz sine out on my unit has some noticeable amplitude noise, at least a few %. Since I'm only using the signal as a digital clock, I prefer a square wave, assuming the fast edge will give me lower jitter. A 200 MHz Rigol scope reads a risetime of 2 ns on CPLD pin 49, but the waveform looks so noisy and odd (see below), maybe I would be better off just squaring up the output sine. ...maybe if pin 49 was disconnected from the sine output filter, it would be more square (?) https://picasaweb.google.com/109928236040342205185/FE5680A#5685304143859526258 -John Beale ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] troubleshooting a FE-5680A (got two; only one works)
Just yesterday I received two FE-5680A units from China. One of them works and one doesn't achieve lock. Both are labelled with FEI P/N 217400-30352-1. Here's a photo of the one that works, the other looks just the same but different serial number. https://picasaweb.google.com/109928236040342205185/FE5680A#5680473663653140162 FE-5680A Rb #1: At startup, RF out (pin 7) ramps from 9.999828 to 10.66 MHz for a few minutes, then locks at 10.00 MHz and pin 3 drops low. The RF signal is about 2 Vpp. Power draw at startup about 25 W, dropping to 10 W. FE-5680A Rb #2: RF out scans from 9.999799 to 9.94 MHz repeatedly, and does not achieve lock. Pin 3 remains high. The RF signal is about 1 Vpp (half the level of the working unit). Power draw similar to unit #1. Any suggestions for what might be done to prod the 2nd unit towards working? I see some things which might be trimmer caps on the board, and what might be a round heating element(?) soldered to a crystal can in this photo: https://picasaweb.google.com/lh/photo/0WRM10pGG0Kd89Ji80yoa9MTjNZETYmyPJy0liipFm0?feat=directlink thanks for any advice! John Beale N8JUF ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] troubleshooting a FE-5680A (got two; only one works)
[Peter Bell] ...check to make sure that the VXCO is actually sweeping through 10MHz - if not, you can try adjusting C217 to centralise the sweep range. Thanks Pete, you are exactly right. As mentioned, the VCXO was sweeping from 9.999799 to 9.94 MHz with no lock. I found that the C217 trimmer was nearly at minimum C already, but a tiny tweak to move it to absolute minimum C shifted up the center frequency 30 Hz, which (just) enabled a lock at 10.00 MHz. Given the pre-existing C217 setting, I wonder if this unit was marginal even from the factory. I don't know what minimum value C217 has, but I could remove C217 completely which might center it more. Or, maybe there is a way to increase the VCO tuning range, no doubt at a cost in phase noise. Asking for a replacement unit is another option, but I'm just too impatient for that, so I'm taking it as an opportunity to learn something. (in fact I did send him a note, but I'm not expecting anything.) Thanks to Pete and the time-nuts list for the solution! -john ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] FE 5680A new version - Filtering the 10 MHz
Sylvain Munaut wrote: It's not generated from a DDS. It's from a xilinx PLD, then through an L and then through a C to the RF connector. The signal at the L output is fairly sinusoidal (at least monotonic near the crossing), but after the cap, it's like that ... While I'm waiting for my own FE-5680A to arrive... that sine wave certainly looks awful. What kind of signal is coming from the Xilinx PLD pin, before the L? Is it a simple 10 MHz square wave, or some kind of 10MHz PWM intended to approximate a 10 MHz sine wave? If it is a 10 MHz square wave, can I use that as a 10 MHz clock directly (probably through a digital buffer) or does it have a lot of jitter, which the LC filter was supposed to smooth out? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] FE-5680A Rb lamp subject to wearout?
I've decided I can't pass up a rubidium standard at this price, having seen the reports here that the units work. Just one question: it was my impression that the rubidium in such a device gets somehow used up over time. Can anyone hazard a guess as to how long this might keep running? The FE-5680A data sheet at http://www.freqelec.com/pdf/rfs_12pg.pdf seems to be silent on the subject of wearout. Should I expect that this sort of repair procedure will soon be necessary? http://www.ko4bb.com/Manuals/05%29_GPS_Timing/Efratom/Efratom_FRS_Lamp_assembly_repair.pdf ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] another use for GPS: detecting underground nuclear tests
Even underground nuclear tests leave their mark on the part of the upper atmosphere known as the ionosphere, the researchers discovered, when they examined GPS data recorded the same day as a North Korean nuclear test in 2009. Within minutes on that day, GPS stations in nearby countries registered a change in ionospheric electron density, as a bubble of disturbed particles spread out from the test site and across the planet. Jihye Park, a doctoral student in geodetic science at [Ohio State University], is presenting the results of the study this Wednesday, Thursday, and Friday in a poster session at the CTBTO meeting in Vienna, Austria. ...from http://researchnews.osu.edu/archive/gpsnukes.htm ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] PIC processor CTMU module used for sub-ns TIC applications?
I see Microchip application note AN1375 at http://ww1.microchip.com/downloads/en/AppNotes/01375a.pdf suggests that the CTMU module included in some recent PIC parts, for example PIC18F46J11 can be used as a TIC building block for interpolating time intervals with sub-ns resolution. I gather this module was originally designed for touch sensing applications; they also mention measurement of absolute and relative capacitance. The application note merely asserts the possibility, but neglects to present a specific design. Has anyone here attempted to use a PIC CTMU in that way? I've been studying Richard McCorkle's PICTIC-II design (1) with an eye to implementing the digital parts in a CPLD, and so far have a start/stop counter working (2). I haven't yet started on the analog part of the circuit, but now I'm wondering if Microchip has already done the work for me, in a $4 part ? (3) (1) http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:pictic (2) http://bealecorner.org/best/measure/time/CPLD-TIC/ (3) http://parts.digikey.com/1/parts/1671850-ic-pic-mcu-flash-64kb-44-tqfp-pic18f46j11-i-pt.html ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] how to set up a Jupiter-T?
In case anyone's interested, I've discovered a few things about my Jupiter-T: 1) WinOncore12 sends commands too quickly. The TU60 needs quite some time to process each one. If I type the commands in by hand separately, more of them work as expected. 2) Typing the command @@Ae will set longitude, but reports longitude 0 and 8000 reports 37 degrees East, and is about 74 degrees East and that's the largest allowed value. So either on sending or receiving, or both, I think WinOncore12 is interpreting the data fields differently than the TU60. Or you can't use this device in the west :-) 3) Don't try to use *bay GPS Antenna Item: 260664041419 including 10-meter lead to MCX connector, it doesn't work. Not even on a different, known-good receiver. Might have too high a gain (55 dB??) Or I just got a bad one. -John On 4/9/2011 8:00 AM, John Beale wrote: Navman TU60 Jupiter-T COPYRIGHT 1995-2004 NAVMAN LTD. SFTW P/N # SOFTWARE VER # 93 SOFTWARE REV # 07 SOFTWARE DATE 01/16/2004 MODEL # R01 HDWR P/N # TU60-D125 SERIAL # 703127719 MANUFACTUR DATE 701//52030 OPTIONS LIST 5843 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] cheap 5V OCXO in 14DIP has about 1E-9 drift per day
Just FYI, I'm not sure how this compares to other similar parts, but I'm seeing about +/- 1 ppb (1E-9) frequency drift per 24 hour period from one sample of the Pletronics OHM40480526, which I've had running for about 10 days now. It runs on +5V and after a warmup current of 250 mA for a few seconds, it draws about 60 mA steady state at room temperature. I'm driving the tuning voltage on pin 1 from a separate +5V reference to avoid variations due to heater current shifts. I use a simple resistive trimpot divider to set the voltage, this is not a GPSDO (yet :-). I'm sure most on this list have more refined tastes in oscillators than this one (and probably want 10 MHz instead of 26 MHz), but I thought it noteworthy because it is so cheap. These parts are currently available online for $2 each. I'm not affiliated with the seller. a few more details: http://www.bealecorner.org/best/measure/time/Pletronics-26MHz-OCXO-tuning.pdf http://www.bealecorner.org/best/measure/time/26MHz-osc-notes.txt ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] semi-OT: comparison of two 10x scope probes (cost $7 vs. $406)
I am always loosing the little hook adaptor on the end of my scope probes so I went looking for replacements. I noticed that I could buy a pair of complete 100 MHz probes including tip and ground clip online for $13 shipped from Shenzen China. Didn't expect much, but this application was for low speed signals anyway and I got some. Couldn't loose at that price. I figured the hook tip adaptor alone was worth it. They arrived the next week and just for fun I compared my new $6.50 probe with a 500 MHz Tek P6139A probe, using a not terribly fast scope, the 100 MHz Tek TDS 220, and a signal of unknown risetime, the output of a 26 MHz Pletronics OCXO in a 14DIP can (by the way these go for $2 online, the cheapest OCXO I've seen). This was just a quick casual comparison, not to be taken too seriously. I was somewhat surprised to see the cheap probe presented the same 3.8 ns risetime as the Tek probe on this scope, although it comes with some ringing also whereas the Tek probe did not show ringing. Both probes were used in the same place, ground directly to probe shield without flying ground leads (although the circuit itself was casually constructed and had about 1 length of ground return). If you had a simple 1-pole 100 MHz lowpass you'd expect 3.5 nsec risetime so this is in the right ballpark for scope rated at 100 MHz (and my source signal may be no faster than that anyway- I haven't built an avalanche pulse generator yet :-). Scope photo showing the comparison below. The cheap probe trace is shown as RefA (light grey) and the Tek probe is CH1 (dark grey/black). https://picasaweb.google.com/lh/photo/1_SVMQ3ajYJUARc51BXnzw?feat=directlink ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] semi-OT: comparison of two 10x scope probes / cheap OCXO
Yes, I am controlling the OCXO frequency with a voltage input (center tap of 10k trimpot from +5V to ground). I hooked up my custom 26 MHz PIC divider* and was able to trim the OCXO to match the output of my GPS 1pps signal to better than 1E-9 (at least for short periods of time). These parts draw about 60 mA at +5V in operation in a 23 C ambient environment, after a brief one-time warmup pulse of about 200 mA. The can gets a bit warm if left open. I taped a small thermistor against the case, and made a little styrofoam box to nest snugly over it and measured the can case temp to reach about 50 C when thus insulated. I am accumulating some performance data on the two units I have and can post it online if anyone is interested. (actually, I was thinking of buying a bunch more before posting the data, because the price seems too good to be true). * http://www.bealecorner.org/best/measure/time/source/ Scott Newell wrote: That's a great price for any OCXO. Do they have EFC? (I can't tell from the part number in the auction photo.) At 01:41 PM 3/17/2011, beale wrote: output of a 26 MHz Pletronics OCXO in a 14DIP can (by the way these go for $2 online, the cheapest OCXO I've seen). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] looking for algorithms to locate edge location in noisy data
I'm just starting to play around with some timing signals. I'm just wondering if some of you experts can refer me to some reading on algorithms to find the location of an edge in noisy data. For example, this waveform: https://picasaweb.google.com/lh/photo/aPZbcgu9neWRJAGd_VoGng?feat=directlink Now, I know I've got every kind of analog signal problem here, very low bandwidth, random length wires instead of a proper scope probe, unterminated lines, vertical scale that doesn't use the scope's already limited 8-bit dynamic range etc. I can improve the signal, but I'm just using that trace to illustrate several issues in general. I wonder what a good algorithm or procedure might be to extract the best available edge timing resolution from a set of data describing a waveform of this approximate shape. In this case, by best I mean the most repeatable result in the face of a bandwidth-limited signal with given level of random noise and quantization error. I imagine I would want to generate a prototype waveform and then slide it back and forth over each given waveform in turn, and look for the best match position (cross correlation) ? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] help with initial setup for Motorola M12+T GPS? is my board dead?
On 3/4/2011 11:54 PM, John Beale wrote: The TX line out of the board just sits quietly at +3V. Is there anything obvious I should be trying? Er.. nevermind. It seems that swapping TX and RX helped. Sigh. --- COPYRIGHT 1991-2000 MOTOROLA INC. SFTW P/N # 61-G10002A SOFTWARE VER # 1 SOFTWARE REV # 3 SOFTWARE DATE Mar 13 2000 MODEL #P183T12N12 HWDR P/N # 1 SERIAL # P0171Z MANUFACTUR DATE 1J12 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] difference between Oncore M12 and M12+T (useful when buying online)
In case anyone else is shopping online for a used Motorola Oncore M12+T timing GPS, it's probably useful to know what I just learned: Some online sellers offering M12+T 100 pps GPS may instead send you a M12 Navigation (non-timing) GPS. The differences: Motorola Oncore M12 Navigation GPS: --- * Supports Motorola Binary and NMEA output * does not have 100 Hz output * does not have TRAIM (Timing Receiver Autonomous Integrity Monitor) * does not have sawtooth correction output * 1 PPS 500 ns timing crystal nearest MMCX antenna connector is two-lead can style with bent leads for surface mounting example p/n label: P183T12N12 (final N = Navigation?) photos: http://www.wa5rrn.com/GPS%20Other/Motorola%20M12/m12.pdf https://picasaweb.google.com/bealevideo/GPS#5580118907079326290 Motorola Oncore M12+T Timing GPS: --- * Supports Motorola Binary output only * 1 Hz or 100 Hz output selectable * TRAIM (Timing Receiver Autonomous Integrity Monitor) * sawtooth correction (clock granularity) message available * 1 pps 2nS 1 Sigma, 6nS 6 Sigma (using sawtooth correction message) * 1 pps 10nS 1 Sigma, 20nS 6 Sigma (without correction) smaller leadless surface-mount crystals example p/n label: P283T12T17(final T = Timing?) photos: http://www.wa5rrn.com/GPS%20Other/Motorola%20M12/m12plusbrochure.pdf http://cgi.ebay.co.uk/ws/eBayISAPI.dll?VISuperSizeitem=290308535362 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] help with initial setup for Motorola M12+T GPS? is my board dead?
I just received my first real piece of time hardware, a M12+T timing GPS. At least, that's what it's supposed to be, it doesn't actually have any label saying so. I got it online from this seller: http://www.ioffer.com/i/Motorola-ONCORE-M12+T-timing-gps-receiver-1pps-100hz-105387652 The board I received looks like this: https://picasaweb.google.com/bealevideo/GPS#5580118907079326290 I got the 2x5 0.05 connector, built a 3.0V power supply, and hooked up the serial lines to a FTDI USB-to-serial (3.3V logic level) board, and am trying to talk Motorola Binary at 9600 baud to it using WinOncore12. I tried the setup receiver wizard, the GPS self-test, and uploading an almanac. My scope shows the serial data from the PC going into the board, but no signals ever come out. The TX line out of the board just sits quietly at +3V. Is there anything obvious I should be trying? Thanks for any help! ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] yet another version of PIC 1pps code, for 16F1823
I got some of the cheap Pletronics OHM40480526 26MHz OCXO parts for experiments (couldn't resist $2 each :-). For this purpose I modified the Richard H McCorkle/Tom Van Baak code for generating a 1 pps output from a PIC, to work with 26 MHz input, and also target the PIC 16F1823 since that's the part I had handy. But, being new to the PIC16F family it took some time to get all the configuration bits correct. So in case anyone else is in that position, here's the code I ended up with: http://bealecorner.org/best/measure/time/source/PIC16F1823-26MHz-1pps_asm.txt My M12T+ GPS board is coming on a slow boat from China, so I don't yet have any real standard to compare this with. But I set up two OCXOs driving two PICs, and compared the two 1pps outputs on a 2-ch scope, after tweaking my 10k 10-turn trim pot feeding the ADJ pin on one part to be pretty close in frequency to the other. I see a slow steady increase in phase lag, accumulating 167 ns in 7 minutes, so I have a frequency difference between my two oscillators of 1.67E-7/420 = 4E-10 or 0.4 ppm. For better measurements I guess I want a PIC-TIC or equivalent. -John Beale ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] advice: frequency calibration to 1 ppm possible without GPSDO?
Hi Kasper, Thank you, your nft program looks very interesting! It turns out the local ISP that provides my DSL, sonic.net runs a GPS-driven NTP server and I have a pretty low and stable latency, so this may work well. To measure a relative frequency offset, I presume that what limits accuracy is the total length of time of the test. So with a stable latency, I should not need to poll the server very often. Meanwhile I have a M12+ timing GPS and antenna on order, and am assembling some glue logic, case, 3.0V power supply etc. I may not ever manage a long-term GPS installation, since my apartment is surrounded by tall obstructions, and my workplace has metallized-film window panes which block all GPS signals, and no roof access. It has a big open parking lot, though... I imagine using a car-mount GPS setup and sending a 1 Hz or 100 Hz LED or laser pulse up through the window to a telescope / photodetector at my workbench on the 2nd floor or maybe sending a frequency-locked 10 kHz tone through a FM wireless mic system would be adequate. -John Beale I did a piece of software to provide calibration to equipment-deficient microcontroller-hobbyist frequency counter builders (think 100ppm crystal from the bin) over ntp: http://n1.taur.dk/nft/nft.pdf /Kasper Pedersen ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] advice: frequency calibration to 1 ppm possible without GPSDO?
Hello time enthusiasts! I'm hoping for your advice on my (perhaps modest, by this list's standards) project. I would like to make a frequency calibration of a 10 MHz oscillator to 1 ppm (1E-6) or better, using some basic equipment. I do not have a GPSDO or any serious lab equipment, or budget for same as this is just a personal project. What I do have access to: 10 MHz uncalibrated TCXO (K1602TE in 14-pin DIP can from online auction site) Optoelectronics 3000A+ frequency counter (I believe stable to 1 ppm, but not recently calibrated) Sony ICF-2010 shortwave radio (consumer item, possibly stable at 1 ppm level) Tektronix TDS220 (basic digital scope) Saleae Logic analyzer (software-defined logic analyzer, the datalogger part has generic 24 MHz xtal) PC running Windows XP Is it possible to calibrate my 10 MHz oscillator to some standard reference source at the 1 ppm level using these tools? I also have a PIC programmer so I could construct a decade divider chain, etc. if that was useful. So far, directly counting the 10 MHz signal using a 10 sec gate, the count varies about +/- 1 Hz (0.1 ppm) over several hours of measurement. However, I don't know if the oscillator or the counter drifts more, or if either one is close to being accurate. My first try at a standard reference was to monitor the WWV broadcast at 5 MHz, pipe the output into the PC and view it with DL4YHF Spectrum Lab. I found the WWV signal wandered around over 10 Hz (2 ppm) during the night and faded at sunrise without ever stabilizing, so that doesn't seem too encouraging. I don't know if there are any stable signals in groundwave range. I've read about using an analog TV horizontal flyback signal when locked to a network broadcast, but I'm just a bit too late for that technique to work! Likewise with the Loran-C receiver a guy at a local ham club has. I assume any accessible signals on my HDTV are internally synthesized with dubious accuracy. I have DSL on my phone line, but I don't know if there's any useful standard frequencies there and I don't think I'm supposed to directly probe the phone line anyway. Comparison to a GPS frequency standard would obviously work and since I live in Mountain View, CA there's probably some within walking distance, but I don't know anyone in the metrology community. Thanks for any suggestions or insights into this question! John Beale N8JUF ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Freq cal to 1ppm without GPSDO
Hi Murray, Thanks to you and the others for your replies. After some more HF reception problems here, I have come to the same conclusion as you. I found an Oncore M12+ timing GPS is available pretty cheap from Hong Kong, so that's my plan. best regards, John Beale 1. My best advice is to get hold of a cheap GPS module with a 1pps (seconds pulse) output. Connect it up, and when you have a fix, use the 1pps to trigger your digital oscilloscope. Set the timebase to 1us/div to start with, and ultimately 100ns, and observe the 10MHz output of your TCXO. You will see the waveform drifting slowly. Counting how long it takes to slip one cycle will tell you how far off the TCXO is. If you have a counter with Time Interval mode capability, you could use that, using the GPS to start and 10MHz to stop, again observing the drift. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] temperature stability basics
In an attempt to educate myself about temperature stability, I put a temperature sensor in a 1 cube of brass wrapped in plastic packing-type bubble wrap, and compared that with another sensor outside the bubble wrap, with the whole combination in a thin nylon case just to slow down direct air drafts. I put it on the bench in the office where the ambient temperature varies up and down by a few degrees over the day. I recorded both temperatures with milli-degree resolution. Looking at the resulting plots, it looks like my thermal mass and thermal insulation on the inside sensor gives me only about a half hour lag at most relative to the outside sensor (hard to say exactly, it doesn't look like a simple one-pole filter). Note, I am not attempting any kind of ovenized control as yet, just measuring some time constants. I've read that plain bubble wrap has an R value of about 2 ft^2·°F·h/(BTU·in), while some types of rigid foam building insulation go up to R=8 (at least until the CFC gases used to blow the foam leak out). What is done in real instruments that need good thermal insulation? I assume dewar flasks are limited to aerospace applications. Photo of the block prior to bubble wrap: http://picasaweb.google.com/bealevideo/2010_11_18TempExperiment (live) plot of temperatures: http://www.pachube.com/feeds/12988 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] DS1620 Variants in the Thunderbolt
E (bad) revision wasn't used until late 2004. My understanding of the current DS1620 data sheet is that you can better than 0.5 C resolution, by reading some extra registers and doing a subtraction and a division, as mentioned below. Just wondering if this is something that could be accessible in a recent Thunderbolt, or is the firmware not modifiable, and the chip's 3-wire interface is not available externally? http://datasheets.maxim-ic.com/en/ds/DS1620.pdf Higher resolutions may be obtained by reading the temperature, and truncating the 0.5°C bit (the LSB) from the read value. This value is TEMP_READ. The value left in the counter may then be read by issuing a READ COUNTER command. This value is the count remaining (COUNT_REMAIN) after the gate period has ceased. By loading the value of the slope accumulator into the count register (using the READ SLOPE command), this value may then be read, yielding the number of counts per degree C (COUNT_PER_C) at that temperature. The actual temperature may be then be calculated by the user using the following: TEMPERATURE=TEMP_READ-0.25 + ((COUNT_PER_C - COUNT_REMAIN)/COUNT_PER_C) John Beale (list lurker - first post) N8JUF ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
