[time-nuts] Raw phase data of super-5065
Saw the plot in the June 12 post. Pretty much limited by the 3816 up to 10K Seconds. Would be interesting to see a long plot of the two 5065 against each other! Cheers, Corby ___ 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] HP5065C or the 5065Jr.
Joe, "What is mounted on top of the 10811?" That is a Clifton Labs Z1 buffer amp. Still made but by another company. Mounted on a small right angle bracket that is mounted using the existing screws on the back of the 10811 adaptor assy. It's input is connected to the 10Mhz out pins of the connector for the 10811. It has a high input impedance so as not to load the 10811 and VERY high isolation. That's how I provide the 10Mhz out. I have also used the LH0033 mounted with RTV "dead bug" style on the on the back of the assy. It only requires two resistors and two caps to utilize a single supply. Cheers, Corby ___ 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] Raw phase data of super-5065
Attila, I will send you some raw data. Attached is a combined plot of a recent successful filter installation. Only 20 to 25% of units will be improved with the filter mod. Two things to look for. 1- The short term stability at 1 Sec (Allan Deviation) should drop from the 2X10-12th range down to the mid -13ths. 2- The Allan Deviation plot should drop into the -14ths between 32 and 64 Seconds. #1 is easily tested but not many have a reference to test #2 against. Also as Bob indicated longer term plots need to be in a benign environmental setting. Cheers, Corby___ 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] how long dues this rubidium standard last for
Paul, I agree with Bob, the small telecom ones to include the Efratom ones have a lifetime that is just a guess at this point. A brand new PRS10 with a warranty and the original owner repair discount would be a good bet, they do however have lamp assy problems unless that has been redesigned. The HP5065A however has no significant failure modes, and I have worked on and seen good performance out of 40 Year old units! As discussed here before 5065A performance leaves the others "in the dust". The filter (either Edmund or Thor labs sell them) will run about $170-$200 however you cannot guarantee a performance increase with every 5065A as there are other parameters that must be met. The main problem is finding one that is affordable! Due to it's excellent short term stability (<1.5X10-13th at 100 Sec) it's in high demand and prices have been increasing as the available ones get snapped up! As Bob noted a last production serial number (prefix 2816A) recently went for $4000.00 Mid vintage ones can run $2000.00 If you don't need the 5065A performance then just buy a telecom one whenever your current one dies! Cheers, Corby ___ 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] HP 5061A and 5061B modules clear out!
Hi, I'm cleaning out a BUNCH of modules from HP 5061A/B. See listing on eBay below. More lots of other modules to follow in groups that will fit into flat rate boxes. If you have specific wants contact me off list! Cheers, Corby https://www.ebay.com/itm/HP5061A-5051B-A7-AC-amplifier-modules-eight-Freq uency-standard-Cesium-standard/323183182781 ___ 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] What does determine the short term stability of an Rb vapor cell standard?
Here is an clip from one of the space qualified ones Bob mentioned. "The RAFS employs classical rubidium gas cell atomic frequency standard principles. It utilizes a physics package with a discrete isotopic filter cell for best stability. The relatively large, cool absorption cell provides exceptionally high signal-to-noise ratio and excellent short term stability. The addition of a thin film spectral filter increased the signal-to-noise ratio even higher." Highlights are: -"classic" architecture, meaning a separate discrete filter cell. -"large cool absorption cell", the 5065A cell is large and runs at around 65 degrees C. -"thin film spectral filter", this is what the "super" mod adds to the 5065A Telecomm comparisons are: (not universal) -small size combined filter and absorption cell, This requires a "hot" cell, well above 65 degrees. -only a few have spectral filters. Conclusions: - A bigger cell is more stable than a smaller - a cooler cell is more stable than a hotter - a separate discrete filter sell allows higher stability than a combined arraignment. - These requirements run counter to the telecomm requirements of low power, small size, fast warmup, and LOW cost. Cheers, Corby ___ 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] Replacement Backup Battery for 5065A?
I agree with Bert, I always remove the battery. They will cause grief eventually! Use either in UPS or the separate DC input jack on the rear. One note, if the battery is removed and the battery charge switch is in the position to light the front panel lamp you will degrade the stability of the unit! Removing the bulb clears it up! Never bothered to figure out why! Also I usually remove a battery A2 and install two shottky diodes on the underside of A2s chassis jack. Non-battery units have an A2 that just has these two diodes on it. Cheers, Corby ___ 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] Replacement A9 boards for the HP 5065A
Well I hunted up the change pages for the A9. The cap is polycarbonate, the original A9 was polyester. If I can't find the polycarbonate I'll look into the PPS. Cheers, Corby ___ 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] Replacement A9 boards for the HP 5065A
Hi, I'm working to make some replacement A9 boards for the HP 5065A to the new style schematic. Will share the Gerber file when done. The integrator capacitor is a 1986 vintage TRW 5.0ufd 50V 10% .42"DX1.0"L axial. Of course it has an HP part number and no manufactures #. Any guess as to what type it is? Polycarbonate, polypropylene, ??? Just wanting to find a good modern replacement for its use. (Integrator with a 50ms time constant.) Thanks, Corby ___ 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] Selling Time and Frequency Equipment Or "just saying"
First, full disclosure, I have no vested or financial interest in the 5065A he is selling. Now the 2816A prefix is the last series built so the most modern. The last one I remember on eBay went for OVER $4000.00 Comparing a 5065A to a Cesium (except maybe a working 5071A for the same price)\is worse than Apples and Oranges. Ask Bert who got rid of his 5065A years ago because he had a Cesium, he regrets that now and just got a new one! A 5065A buyer is looking for the best short term stability he can find (nominal 1.5X10-13th at 100 Sec) Keeping on frequency is easy via GPS comparisons. A Cesium buyer want NIST traceable accuracy "out of the box" and never (practically) having to adjust the frequency. The Cesium will be worse when compared to the 5065A at shorter Tau even if it has a high performance tube. Another thing to consider when buying a Cesium is what is the condition of the tube. The tube will die, just don't know when. (probably at the most inconvenient time!), and lets not ask what a replacement tube costs! There is no perceptible wear mechanisms in play for the 5065A (I have seen exactly one failed lamp in many years of working on them) Many of the first 1968 series built will still perform to specs today. So, Just saying! Cheers, Corby ___ 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] HP 5065A super
Perrier, The telecom Rubidiums don't leave much meat on the bone for improvements as they sacrificed pretty much everything else to be cheap, small, and low power consumption. Most of these tradeoffs work directly against trying to get better short term stability out of them. Bummer. Cheers, Corby ___ 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] Curious, how many t-nuts have 5065A
Hi, My current Tally of "Known" HP 5065A is 120 units! Cheers, Corby ___ 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] The "NAKED" 5065A optical unit
Attila, The Child and oven windings were destroyed pulling the oven cylinders out of the potting. I suppose you could replicate them and try to repot but I'm never going to try! Cheers, Corby ___ 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] The "NAKED" 5065A optical unit
Paul, You do NOT want to take one apart to this level! It's never going to operate again. If you look at the lamp in the PIX you will see a white coil wrapped around the bulb. This is the tank for the 90Mhz drive and it sits cocked at a 45 degree angle. The lamp assy can be removed easily via 3 small screws and repaired or modified. The Lamp circuit is designed to put out a bit higher RF level and once the lamp starts it drops down a bit. I would question re-engineering the lamp circuit as it can easily reach 1.5X10-13th at 100 Sec stability and 5X10-14th at 100 Sec. with the filter mod. Unless you have a maser or BVA to compare against how will you know if any modifications are going to help or hurt? The only thing I replace even if it measures OK is the 1.33K resistor as it will "crack" eventually and change value. A 1.3K 5% 1W metal oxide works well. Cheers, Corby ___ 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] HP 107BR on eBay
Found a cosmetically nice HP 107BR on eBay right now. Hewlett Packard HP 107BR Quartz Oscillator Vintage Cheers, Corby ___ 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] Rakon HSO-14
Hi, Anyone priced a Rakon HSO-14 option 8. It's the Oscilloquartz 8607 option 8 replacement. I'm almost afraid to ask! Cheers, Corby ___ 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] Time interval measurement vs dual mixer method
Luciano, I don't know of a commercial version. As you have seen as the two signals move away from close phase coincidence the system noise level will increase. This is because the common offset oscillator noise will only cancel when the phases are closely matching. This is mainly important for the lower Tau (like 1 to 10 seconds). I will normally adjust the phase of my reference or DUT so that myTIC is reading 0.0XX (close to phase match) and very slowly rising. (with my setup most DUT will age downward). Then I start logging the data. A typical run with a 1 week aged quartz will show the TIC count slowly increase (and may wrap) and then as the aging continues the count will reverse and eventually go "below" zero and wrap. A phase plot will show a nice parabolic looking curve going up and then as the aging crosses it will curve down. If there are wraps the plotter program can take them out. Any long plot of Quartz WILL wrap! Now if you plot the AD you will see a normal type plot for a good Quartz. If the TIC count increased well past coincidence only the Higher Taus will be accurate. For the lower Tau you need to cut off the data past where it climbed too high. I typically will setup as described and run a short log of say 5 minutes. I might only keep the first 100 Seconds and plot the AD against that. This will give you an accurate plot for the lower Tau. These two plots can then be combined to give you the whole range. The attached plot of an FE405B illustrates this. The Red plot is against a very good FTS 1200 (2X10-13th at 1 thru just past 10 Sec) The blue continuation is against a very good HP 5065A (1.5X10-13th at 100 Sec) So if the lower Tau are important only use logged data that are in near phase match! Hope this helps! Cheers, Corby___ 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] minimalist sine to square
The Efratom/Tektronix PTB-100 took the 10Mhz sine out of the FRK brick, AC coupled it to the input of an 74LS14 biased with a votage divider from +5 to ground. 4 parts! Cheers, Corby ___ 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] Time interval measurement vs dual mixer method
Luciano, Not sure what you mean by "two measures made on the same DUT never coincide". The plotter program takes out wraps which since your phase gain is so large are due to happen. For lower Tau measurements just adjust the phase for close to equal and run shorter plots. These can be spliced into the longer Tau plot. I routinely get repeatable plots on the same DUT with my DMTD setup. Careful setup and understanding what you can and cannot accomplish is the key. Cheers, Corby ___ 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] Some HP 10811 05071-60219 info!
Hi, Attached is a schematic of the changes made to the stock 10811 for use in the HP 5071A. Also while I recently had two of them opened I noticed wavy lockwashers under the nut attaching the tuning capacitor. If you have ever had to open one up to retighten this nut you would wish all of them had the lockwasher! Cheers, Corby___ 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] LED replacement screen for 53131A 53132A!!??
Hi, Saw this on the EEVblog and wondered if it could be done for the 53132A?? https://www.eevblog.com/forum/projects/led-display-for-hp-3457a-multimete r-i-did-it-)/ I'd just be happy with 7 segment hi efficiency LEDs and just a few of the annunciators!! Cheers, Corby ___ 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] Regarding the improved integrator A9 in the 5065A...
Ulf, The new A9 was only installed in units that had the 10811 installed so HP was not concerned with it working with the 105 oscillator. In the 10811 interface the EFC from A9 goes thru a 316K resistor to a 147K (nominal) resistor to ground. This forms a voltage divider the feed the 10811 EFC pin. So the peak EFC the 10811 feels is much less than the A9 output! Cheers, Corby ___ 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] OFF topic! Iridium 4 launch video
Hi, I've worked at Vandenberg AFB since 1971 and have seen LOTS of launches over those years. I was tracking the Iridium 4 launch so could not go outside and watch. However someone made a video that is just Awesome. https://www.youtube.com/watch?v=UU5KpfOT-_Y You see the rocket come over a local hill and then follow it till it drops over the horizon. Since it occurred just a bit after sunset the rocket climbed up into the sunshine after a bit. This is called the twilight effect and in this case was textbook! You will see the plume brighten up as it does. You will see the booster shut down and the rocket spits out of the plume. Then a plume as the booster separates and the 2nd stage fires. Then the FUN begins! As the plume opens up you will see the booster separating from the 2nd stage and it's RCS thrusters firing to position it. Then the thrusters go crazy for a bit as the booster is turned around for the boostback. Also you will see the two pieces of the payload fairing dropping off and their RCS thrusters firing. Then the booster starts dropping rapidly and you see the booster firing to slow it down for a landing as it drops below the horizon. (I believe it just ends up in the ocean as they did not want to refurbish this one.) Then a bit later the 2nd stage also drops below the hill line. This is the coolest video I have seen of a launch. Cheers, Corby ___ 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] question about HP 5601a harmonic generator
When working on the A4 assy. the ONLY adjustments you should make are: - Cavity frequency, unscrew locking ring and while looking at the A7 J1 signal or 2nd harmonic reading adjust for max and then lock down. - Attenuator, Unlock with allen, adjust for same, usually pulled all the way out. Remember to lock. -S5 the one by the attenuator, only needed if tube swapped but if you adjust make sure the peak does not slip when you tighten the locknut. - the top pot, adjust for the same. - If you adjust any of the other locknutted plungers you will NEVER get back to where you need to be Cheers, Corby ___ 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] HP5065 - Some OP-Amp, FB and Teflon ...
Here is the schematic of the new style A9. Cheers, Corby___ 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] HP5065 - Some OP-Amp, FB and Teflon ...
Ulf, Forrest is correct. I'd try the LT1793. It's an SOIC but if you are making your own board that would not be a problem. It is $4.87 at DigiKey. Cheers, Corby ___ 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] Some more info on the 5065A optical unit
Bob, The cardboard is impregnated with the foam insulation goop and then sealed under the foam layer. It is totally sealed off from any environmental effects. Cheers, Corby ___ 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] Some more info on the 5065A optical unit
Made some measurements on a 5065A optical unit. -There are 3 layers in the magnetic shield. -There is about 1/8" of insulation between the outer and middle, and between the middle and inner shields. -The C-field winding is wound on a cardboard form that fits tightly into the inner shield. -There is almost 1/2" of foamed insulation between the C-field winding and the cell and oven forms and windings. Per Poul-Hennings data a 3.25 deg C change of the outer shield will result in a 1 deg C change in the C-field coil. This equates to a 3.4X10-14 frequency shift when not using active current drive. If the outer shield is actively held to plus/minus 1 deg C then the shift will be held within plus/minus 1.05X10-14 as long as the ambient temperature stays within the regulating range of the PC liquid cooler. Cheers, Corby ___ 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] HP 5065A - Some OP-Amp, FB and teflon stand off questions...
Ulf, Be careful if you are going to duplicate the new style A9 for use in a chassis that was built for the old style! On the old style chassis one of the resistors is mounted on the rear of the front panel loop switch. This resistor is mounted on the A9 module for the new style chassis. Which teflon feedthrus? The ones for the DC connections to the metal modules? Cheers, Corby ___ 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] HP5065A C-field mods and optical unit mods
HP5065A C-field mods and optical unit mods The contribution of the temperature coefficients of the fixed resistors and the pot (which is a 21 turn bulk metal foil 10PPM/Deg C pot) show up as frequency errors as shown for several combinations. Note that the pot does not cover the entire 2X10-9 frequency range. There is a high, mid, and low switch setting that shorts both 1k, one 1k, or neither 1k resistor that in conjunction with the pot allows the entire range to be covered. This allows the pot to have a finer frequency resolution A- With only the 2.4K in circuit with the pot at zero Ohms a 1 Deg C change will cause a 2.8X10-15 frequency change. B- With the 2.4K in combination with the pot at 1K a 1 Deg C change will cause a 8.55X10-15 frequency change. C- With the 2.4K in combination with the pot at 1K and both 1K resistors in circuit a 1 Deg C change will cause a 3.99X10-15 frequency change. If in example C you replace the pot with a 100PPM pot a 1 Deg C change will equate to a 2.45X10-14 frequency change. As you can see this circuit will work quite well in eliminating any power supply related C-field changes. Now the C-field coil is only partially temperature regulated by the ovens in the optical unit as they regulate the lamp and cell temperatures and the C-field is not co-located. That is why I'm going to use the PC liquid cooler to actively regulate the temperature of the sealed enclosure I have placed the optical unit into. Cheers, Corby ___ 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] HP5065A C-field mods and optical unit mods
Warren, Most all Rubidium standards do not have active current drive. The HP 5065A is the exception. However the mod I installed is not active. The C-field coils are roughly temperature compensated as they are near the cell oven that is regulated. If you check out Poul-Hennings "hacking the 5065a" you will see that the C-field coil does exhibit some temperature effect even with active current regulation, and the stock C-field circuit also introduces some effects. Now these amount to a small coefficient but we are Time Nuts here so we can do better! My circuit gives a precise current into the coil (for a fixed temperature of the coil), and with the active temperature stabilization I am adding to the outside of the sealed optical unit enclosure those effects will be eliminated. Cheers, Corby ___ 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] HP5065A C-field mods and optical unit mods
Attached is the schematic of the C-field supply. Cheers, Corby___ 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] HP5065A C-field mods and optical unit mods
HP5065A C-field mods and optical unit mods In addition to the power supply mods: -removed AC components -power now supplied with an external DC lab grade low noise highly regulated supply. -temperature coefficient of +20 Volt supply adjusted to be below 1PPM/deg C See: https://www.febo.com/pipermail/time-nuts/2017-August/106634.html I've now installed the improved C-field circuit that has less than +- 1PPM variation per degree C. The optical unit has been installed into a sealed enclosure that has been purged with dry Nitrogen. This eliminates any Barometric pressure effects and also eliminates drift caused by Helium permeation. Tests at this point show a very nice long term stability. Last mod will use a small PC closed loop liquid cooler to keep the outside of the sealed enclosure at a constant temperature essentially making it a double oven. I'm also working on: An active temp compensation scheme to add to the active barometric compensation I outlined earlier. See: https://www.febo.com/pipermail/time-nuts/2016-May/097829.html And a passive optical unit temperature compensation using a thermistor/resistor arrangement. PIX shows the sealed optical unit installed into a slightly taller chassis. (The 5065C ?) Cheers! Corby___ 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] Resoration of 5065A - continued/old style A7
Ulf, You either should replace the -6010 old style A7 or if building one from scratch build the late style. The new style has a BP filter on the 2nd harmonic that makes the 2nd harmonic reading a better indication. On the old style as you adjust the CF (in open loop) you will see the 2nd harmonic reading rise! This is bogus and caused by the 137 Hz signal bleeding through. On the new style when you move off frequency the 2nd harmonic reading drops as it should! Cheers, Corby ___ 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] HP5065A +20V supply and C-field mods
HP5065A +20V supply and C-field circuit mods I'm doing some more work on the 5065A and thought I'd share the results of a modification (one of several that will be done on this unit). I measured the +20V P/S temperature coefficient and got -13.5ppm per degree C. This equates well with the 1N938 10ppm/C and the voltage set resistor TCs of plus/minus 10ppm/C. However the TC varies if the C-field pot is changed. The original circuit has 11.9ma thru the reference diode series resistor (925 Ohm)for a diode current of 6.8ma and a C-field pot circuit current of 5.1ma at midrange on the pot. (zero TC on the diode is specified as 7.5ma) The diode current ranges from 5.3 to 7.8ma depending on the C-field pots position. Since I am replacing the C-field circuit, the C-field pot circuit has been removed. The 925 Ohm resistor was replaced with a 1ppm/C 1K resistor and a 1K precision pot. This allows the Reference diode current to be adjusted to compensate for all the elements in the circuit. (The TC of the diode changes depending on the diode current) After adjusting the diode current and temperature over many iterations and monitoring the +20 Volt output I was able to find a diode current to bring the +20 Volt output coefficient to below 1ppm per degree C! (-.6ppm/C) So that part of the mod is done. Next I will be installing a new C-field current source that has a TC of 2ppm per degree C. Then I'll do some long term plots against the Maser to see if the long term stability has improved at all. More to come! Cheers, Corby ___ 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] Machining some aluminum help!
Well I did some research and found my new best friend! If you remember I needed: "I have a square aluminum tube 5" X 5" with a .25" wall it's 8 1/2" long. I need 20 holes in each end tapped for 4/40 and 1/2" deep." This for a Rubidium standard I am working on. I found all about self forming taps! I drilled the 20 1/2" deep holes and then made a handwheel to attach to the pulley on my drill press. After mounting the tap in the drill press and putting a dab of Crisco on the tap I was able to tap each hole to a depth of 7/16" as fast as I could turn the handwheel! I then got another 8-32 self forming tap to do the holes for 15 feedthru capacitors, again as fast as I could turn the handwheel. I'm very happy to discover these taps Cheers, Corby ___ 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] HP5061B Versus HP5071 Cesium Line Frequencies
Donald, Will look forward to seeing your Allan Deviation plots before and after. That will be the only way to verify your modification will make any improvement. I suspect the improvement at a few seconds will degrade it at other Tau. Cheers, Corby ___ 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] HP5061B Versus HP5071 Cesium Line Frequencies
Donald, HP changed from 12.631771.6 Mhz to 12.631772.5 Mhz in the later days. The Zeeman frequency changed to correspond from 42.82Khz to 53.53Khz. The 5071A uses a Zeeman frequency of 39.949Khz. I believe they liked the stability a bit more at the different C-field current. Either way will put you correctly on frequency at the output (5 or 10Mhz) See: https://www.febo.com/pipermail/time-nuts/2005-April/018171.html Read Toms reply and my post below his. The 5071A synthesizer is always jumping around to control the C-field. It's basic frequency is 131.8Khz Basic info here. http://leapsecond.com/corby/5071comb.pdf Cheers, Corby ___ 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] Machining some aluminum help!
Thanks everyone. Not looking for a redesign, just figuring out how to get the holes drilled and tapped. I have come up with a scheme that looks promising and will let you know how it goes. The enclosure only has to hold +.1PSI of dry nitrogen without leaking. It will have a pressure sensor inside to allow long term monitoring. >From the feedback and some research I will be reducing the depth of the threaded portion. Cheers, Corby ___ 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] Machining some aluminum help!
Well that generated a lot of advice and thanks for it! I think I might do it myself and go with a 1/2" hole depth and 1/4" threaded depth. I'll get some of that Aluminum Tap magic, some new taps and new drill bits. Good idea about drilling the end plates first and drilling thru to match. Between the end plate and the tube is a gasket that needs to seal pressure and moisture tight. That's why I used 5 per side. Will let you know how it turns out. Cheers, Corby ___ 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] Machining some aluminum help!
Hi, I have a square aluminum tube 5" X 5" with a .25" wall it's 8 1/2" long. I need 20 holes in each end tapped for 4/40 and 1/2" deep. This is for a Rubidium project. The local machine shop want's $360.00 Anyone have a machining setup that could do the work a bit cheaper? If not I'll give it a try myself. Please contact me off list. Thanks! Corby Dawson ___ 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] HP5061B Square Wave Modulation Evaluation
Attached is a plot showing the measured floor of the sine wave loop in the 5061A/B and also in the 5065A, along with plot of an HP 5061B with a high performance tube. The tube is the limiting factor. As you can see the margin provided by the current design is substantial. Also if you look at the FTS 4050 and 4060 that use square wave modulation they are a bit noisier than the HP 5061A/B. If you can provide an Allan deviation plot using the existing sine wave system along with a plot of the square wave modified system doing better I'll be surprised! If you really want to make your Cesiums STS better then I'd suggest building a disciplined clean up oscillator like the Microsemi 4145C. If you look at the Allan deviation plot of the combined 5071A and 4145C you can see it works pretty good. However I'm not sure how good a "cherry-picked" 10811 or FTS 1200 at 6 parts in 10-13th or so will compare to the BVA! Corby___ 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] FTS Ramsey cavity
A friend asked me a while ago why the FTS Cesium tubes were so light. Since they were designed from the beginning to fit in a 5.25" high chassis that cut quite a bit of the weight. However a large amount of weight was saved by using a Ramsey cavity that was not milled from a massive block of copper like the HP tubes use. The HP cavities weighed about 3 1/2 pounds for a standard tube and 4 1/2 pounds for the high performance model. The FTS design weighs a mere 14 ounces. Attached is a PIX of the FTS cavity. Cheers, Corby___ 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] Cesium oven and filament PIX
Attached is a PIX showing (CW from top left) the: >ionizer filament >Oven filaments (STD oven) >standard oven assy >high perm oven assy The HiPerf oven filament is the sealed spiral wound tube on the face of the oven. The posts on the top edge of the ovens is the connection to burn a hole in the burst disc to release the Cesium once the tube is pumped down.. Cheers, Corby___ 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] HP5061B Peak to Valley Ratios
Donald, I agree with John, remove the gearing gizmo from the 10811 assy. the adjust hole lines up any way so no need to drill a hole. you just need a long insulated tuning tool. Also agree that a quick indication of tube operation can be seen if the beam current rises when the mod is turned off. The Cesium tube test, set seen in http://leapsecond.com/corby/HP-5071A-with-5061A-4.docx is essentially a stand alone low frequency coil test. If I can't get a decent LF coil beam current I scrap the tube as it's a waste of time to put in in a unit and try the RF tests. The test set uses a 555 based oscillator. For low frequency tests in an instrument I use a 651B or 204C. Set the amplitude and frequency for a peak on the beam current, make sure mod is off and that you are on the central peak. The figure of merit test in the manual will give an indication of how well the tube and instrument are working, but a definitive test is to perform an Allan deviation of the unit. Cheers, Corby ___ 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] HP5061B Ion Current
Things to be careful about! "I think the final vacuum improvement can be achieved more quickly if the cesium oven is on." The outgassing in a tube that has been off for an extended time is almost all from the oven filaments and the ionizer filament. The metal surfaces are virtual "sponges" and getter any gases that are available. If you turn them on with no protective cycling circuit you run the risk of overloading the ion pump to the point where it cannot pump at all! Don't use the 200Meg divider voltage to determine the output voltage of the supply. Unloaded it is a correct representation of the output voltage. (4Vdc equals 4000V out)However any appreciable load causes a counter voltage that drops the divider voltage a lot! The divider voltage might then read 1 volt but the output voltage is still over 3000V. (it's designed that way to shut off the ovens if the divider voltage drops.)Use a Fluke 80K-40 divider probe or similar on the output as it has a very high input impedance. A recent measurement of 4 A18 supplies shows an output voltage of 3000 V with a 50ua load. Also if testing the supply on the bench you must ground the case of the supply to the minus input pin. If you don't your HV will read half of what it should be. Ion pump supplies for vacuum maintenance like for Cesium tubes, Hydrogen Masers, and some high power Rf TX tubes are just for that, "maintenance". This allows low power consumption, small footprint, and long life. On the EFOS Maser here the ion pump supply has a max rating of 2ma, this for a large 20 liter pump. If you are running a tube at high ion pump currents you might have 20na of beam current but check the peak to valley ratio. Just because you can get to 20 na does not mean the tube is performing well. Running an Allan Deviation plot is the easiest way to know for sure. The oven filaments are very robust, the ionizer filament due to the required shape is not. If you are using the older A11 module then the ionizer voltage is AC and causes vibration of the filament which can result in premature failure. Once HP came out with the new A11 (DC on the filament) they would not honor a tubes warranty if you were using the old style A11. Cheers, Corby Dawson ___ 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] HP5061B Ion Current
If you cannot get the ion current below 50ua or so after a week at 5kV then you are out of luck. Most likely you have resistive deposits on the ion pump insulator. If you can get the tube to give a decent SN at those levels then you can run with the alarm circuit bypassed. I have run tubes a couple years this way (at <50ua) but if you let them sit cold you will have to manually cycle the ovens at turn on until the excess gas load is pumped. If you have a bad ion pump supply when you open it up to repair it I would suggest adding a 66K resistor across the 75K resistor. This will increase the alarm trip up to about 40-45ua. If it's the older one the oil capacitors will need changing as well as the 200Meg resistor. If the later one (in the 5061B) then the 47uf radial cap is open. both these units are interchangeable. One other trick is to use a spark discharge tester (miniature hand held tesla coil used in the neon sign industry) to ZAP the ion pump lead. This can blow out any whiskers that the ion pump has developed. You can also (carefully) with the HV on, remove and replace the ion pump connector a few times. Sometimes you will get a sharp discharge that blows out the whisker. I have used both methods with good success. Cheers, Corby ___ 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] Optical Cesium or maybe Cesium "light"!
Looks like Oscilloquartz is getting ready to sell this commercially! Will give the 5071A a run for the money! Reliability should go way up as: -No electron multiplier -No ionizer filament -No state selection magnets Also all the fiddley bits (laser diodes and photodetectors) are external to the tube and can be easily updated as needed. https://www.slideshare.net/ADVAOpticalNetworking/performance-results-of-a n-optically-pumped-cesium-beam-clock Cheers, Corby ___ 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] Need HP 5061A setup help
Skip, If you are setting against GPS then you are done. For most applications either Zeeman frequency- synthesizer setting will be fine. What the Zeeman adjust lets you do is set the frequency (via the C-field) to within the accuracy specs for the instrument without having to use another reference to do the setting. That's why it's a "primary" frequency standard. If you want to use GPS to tweak it as close to possible go ahead. Just ignore all the Zeeman stuff! Cheers, Corby ___ 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] Antique precision timing device without electronics
Very cool! Thanks for sharing. You could probably use any of the large vintage neon bulbs to replace the missing lamp. Cheers, Corby ___ 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] Early 5065A
Pete, That is a VERY early unit. Those early ones did not have the TED device. I have only seen one unit with an earlier SN! Ohm the lamp oven windings to the threaded post protruding from the end of the optical unit. (should be open) Also check across the oven winding (50 Ohm) If the windings are toast (literally!) I can give you my instructions for removing and rewinding the oven. I also have spare oscillators and some other assys. Cheers, Corby ___ 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] Install a 5061A/B tube into a 5071A!
Well I thought that would get your attention! It's not quite as simple as that, however it CAN be done. First you need a good "mini" tube scavenged out of a 5061A/B. These smaller diameter tubes HP made for 5061A/B replacements are essentially a 5071A tube with different connectors. Then you need an EEPROM removed from a dead 5071A tube that has a thermistor value close to the "mini" tube. Tom Van Baak has the paper on his site, you can read about the results.\ I got installing "mini" tubes into several 5071A units. http://leapsecond.com/corby/HP-5071A-with-5061A-4.docx Also included are the results of using a standard tubes EEPROM on a high performance tube and visa versa to extend the tubes life! Now that I'm done with the experimenting I have two 5071A with good "mini" tubes installed and several good "mini" tubes for sale. Buyers of the 5071A can buy a "spare" tube at a discount. Both 5071A are missing the front door cover and the two perforated side panels. Please contact me off list for details, pictures and plots. Cheers, Corby Dawson ___ 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] Hp5061 Cesium Zeeman adjustment
Paul, The Zeeman frequency you use depends on what synthesizer frequency your unit is set for. Either 48.82Khz or 53.53Khz. See: https://www.febo.com/pipermail/time-nuts/2008-July/032378.html The Zeeman coil is close to a short. You set the amplitude to the spot that gives you the best look at the peaks. Adjust the C-field to land on the central peak. Cheers, Corby ___ 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] HP5065A Rubidium questions: some progress
Scott, The resistor should be 12 Ohms nominal, I'd try installing a 12 Ohm and see what happens. The lamp should light within 10 seconds or so of applying power. If you have a spectrum analyzer you can place a loose wire close to the lamp assy and see the approx 120Mhz signal if it's oscillating! The lamp will be a whitish color when cold and a more reddish violet if hot. Cheers, Corby ___ 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] HP5065A Rubidium question
Scott, If you pull the SMB lamp connector off of the chassis jack you can Ohm out between the center pin and shield. Try both polarities of the leads. If the 1330 Ohm resistor is good you should read around 3330 Ohms. This is the sum of the 1330 and a 2000 Ohm resistor. The 12 Ohm (selected) resistor can also open up sometimes. Cheers, Corby ___ 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] Have done some more cutting on the Cs beam tube
Hi, The tiny coil inside the beam path is the low frequency coil used for DC testing of the tube. The tube shown is a standard performance tube and has no degaussing coil. The flat windings on top of the shield are the C-field winding. The high performance cavity is even "prettier". You can see one at http://www.leapsecond.com/pages/cesium-tube/ Towards the bottom you can see the C-field windings in slots around the circumference of the cavity. BTW in 5071A tubes there is no internal difference between the STD and High Performance tubes. They just run at different temperatures! Saves having to build two different tubes! Some more interesting 5071A tube info will post in a couple weeks!!! (Hint: Run your 5071A HiPerf tube at the Std tube temperature to extend life!!!???) Cheers, Corby ___ 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] HP 5061A Cesium Beam Std
David, I would let it set on the peg in Cs off mode for a fewdays. It can take a long time for some tubes. An external HV supply can also be tried if it does not come down in a few days. If it does come down turn the switch to operate to turn the filaments on. The ion pump should peg again, that's OK it will slowly cycle up and down as the filaments de-gas. Eventually the pump will come down for good and the tube will warm up all the way. Then you can test and see if it has some life. Does your unit have the 10811 style oscillator? Is it a standard tube or a high performance? What is the part # like 1924-00156? I might have a good used tube available if it does turn out to be dead. Cheers, Corby ___ 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] HP 5061A/B Cesium tube conundrum
I've been doing some work on testing some HP 5061A/B tubes and came across something that's not making any sense! The R11 and R12 values marked on the tubes for use with the new style A11 are supposed to reflect a parallel value that is 10X larger than the thermistor reading. This to agree with the ratio of the bridge resistors in the A11 module. For instance a 3112A prefix tube shows values of 3.83K and 42.2K. This gives a parallel value of 3.511K which when divided by 10 gives 351.1 Ohm. The value marked on the tube was 352 Ohm. That all makes sense! Now I have three 3232A prefix tubes and they all do not reflect this ratio. For instance one has values of 51.1K and 5.11K which gives 4.65K. This divided by ten gives 465 Ohms. However the Thermistor value marked on the tube is 915 Ohms! I tested all three tubes and they come up to the proper temperature with the thermistor value marked on the tube. Did HP make a change to the A11 bridge resistor ratio, and if so where did they document it! If not and you used the R11 and R12 values you would seriously overheat the tube! Cheers, Corby ___ 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] HP 5062C Service Manual
Dick, The AC connector used depends on if the unit is an option 010 or not! Regular unit MS3106-14S-5S Option 010 MS3126F14-12S Service manual PN is 05062-90029 Cheers, Corby ___ 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] EFOS Maser turns 34!
"Copper has a quite high temperature expansion, so could you servo that via the cavity temperature ?" To answer, both Copper and Aluminum cavities use the temperature setting to coarse tune the cavity. Fine tuning is via Varactor diode and modern Masers do servo "Auto-tune" the cavity to reduce drift. Corby ___ 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] EFOS2 MASER turns 34!
Tim, The EFOS2 uses an Aluminum cavity! So machining would be easier than Copper! The complete manuals with schematics are on Tom's Leapsecond.com site. Making a homebrew Maser was bandied about a few years ago on TimeNuts. Cheers, Corby ___ 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] EFOS2 MASER turns 34!
Happy Birthday EFOS2 Maser! The EFOS2 active hydrogen Maser at my place just turned 34 years old! Pretty impressive reliability. It is an Oscilloquartz Maser, they are now called T4 Science. I know a guy in Norway that bought the refurbished EFOS3 Maser last year directly from T4 Science! It is 32 Years old! I have had the EFOS2 running here pretty much continuously since Sept 2007. I've had to refill the Hydrogen bottle 3 times. replaced ion pumps 4 times (requires a CLEAN vacuum pumping system) Had to repair one of the ion pump supplies (bad capacitor) Also removed original 1 transistor power oscillator that was used to drive the discharge providing the atomic Hydrogen. I replaced it with a custom class A oscillator amplifier. It uses an Oscilloquartz B5400 Quartz oscillator that has aged very little since 2007! Cheers, Corby Dawson ___ 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] HP5062C Chassis available
Hi, I have Seven HP5062C chassis collected over the years. Not sure how many tubes are installed (I can check) or their condition. I'm pretty sure most of the quartz oscillators are missing but I see two sitting by the pile. Might be a very few modules missing. Most of the top and bottom covers are missing. I'd like to dispose of them as a lot for $500.00. Due to the weight and size I'd prefer local pickup. If no interest I'll pull all the cards and modules prior to scrapping the chassis and sell them as gold scrap on eBay. Also will be selling two or three tested HP5061B with good "mini" (recent smaller diameter) tubes. I'm in Lompoc, CA Cheers, Corby ___ 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] Mystery hp Oven UPDATE
Back in June I picked up the mystery oven assy that turned out to be the oscillator assy. of an HP 106A. Since then I have repaired it and another 106B oscillator assy for a friend. My oscillators main problem was that one of the inner oven windings was open. Just for testing I installed an array of resistors on one end of the oven and surprisingly the unit came up properly! This unit might have been a prototype or special order as there was no fine mechanical tuning of the EFC via an internal pot, just the coarse capacitor tuning. My friends had 3 problems. The temperature adjust pots for both the outer and inner ovens were open! Also after a couple days of operation with the new pots the AGC test point wire shorted internally to the supply voltage. went in and disconnected it internally and routed the test point via an added wire. His unit is performing (AD)at 2.0E-13th at 1 and 10 Seconds! My unit is 3.15E-13th at 32 Seconds and is aging at 4.0X10-11th per day. Not bad for old tech but HP built them well back then! Cheers and Happy New Year, Corby ___ 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] HP53131A RS232 question ANSWERED!!!
Thanks to a reply from Angus the 53131A is sending data every sample now!!! "Something to check - in the 'Utility' menu, if the HP-IB is set to 'Talk' rather than a numeric address, it does just what you describe and only sends data every few seconds. Angus. Thanks Corby ___ 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] HP53131A RS232 question
Scott, Tried reversing connections and the count goes from 4ms to 900+ms which is correct. update goes from about 3 seconds to about 5 seconds with them switched. So the connections were correct with the 4ms reading. Found out that the RS232 is talk only so it would not need any commands or feedback from the laptop. Cheers, Corby ___ 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] HP53131A RS232 question
I've tried all the parameters and the update rate still drops to about once every 3 seconds when I turn print on! You still see the 1pps strobing the input channels every transition even with print on. I was using just pins 2, 3 and 5 on the rs232 and switched to a "full" cable with no improvement. Since the problem occurs even without the laptop connected I don't think it's a cable issue. Do I need to have the laptop issue a GET command or something after each transmission? Heeelp! Cheers, Corby ___ 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] HP53131A RS232 question
I reconfigured for TI with +.7V level 50Ohm and I get a good count. With a TI of around 43milliSec between two 1pps signals the display is updating every second. However if I turn print on the display update slows way down and no longer displays consecutive counts! I know I had this working once!!! Should I be using some other function than print? I just want the hyperterminal to take and log the data! Corby ___ 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] HP53131A RS232 question
Hi, I have not played with my 53131A RS232 for a couple years and have a question. I want to configure it to "talk" to Hyperterminal so I can log some readings. I did the 5 items to configure it: HW pacing (disabled) print on baud rate (19200) parity SW pacing (none) with a 5Mhz input I only get data sent about once every 3 seconds, I thought with a 1 second gate I'd get an output measurement every second? I would think there is plenty of time to output the first measurement before the next one is read! Actual setup I'm wanting to do is time interval (at a 1PPS rate) and log the results. I remember I had it working once and it would be OK as long as I did not exceed around 80% of full scale. If that happened I would only get an output logged every other second. I can live with that part but need to get back to it working below around 80%. Any advice is most welcome! I'm going to configure for the TI and <80% and see what happens. Cheers, Corby ___ 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] Maser Hydrogen supply (was Swagelok and metric tubing question)
The EFOS2 has a small (approx. 4" X 10") aluminium compressed gas bottle. I fill it to about 450PSI and it lasts about 3 years. Most modern Masers use Hydride supplies like the Hydrostik I'm working to install. They can last up to 10 years. This all predicated that you have no leaks! Cheers, Corby ___ 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] Swagelok and metric tubing question
Well it's been an education! First finding out how to identify if the Swagelok fitting is Metric by sight and now how carefully the tubing has to be made to use compression fittings! I just went ahead and got the short section from McMaster Carr. Want to make sure it's right if I'm at 400+ PSI with Hydrogen for years at a time!!! Cheers, Corby ___ 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] Swagelok and metric tubing question
Bob, That's the cheapest I have been able to find it. I'll probably go that route with the expensive version as it's specified for compression. I know the original setup mixes copper and stainless but I have read that is not recommended??? Cheers, Corby ___ 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] Swagelok and metric tubing question
This sound off topic but it's for a Hydrogen Maser modification! The EFOS2 Maser is running low on Hydrogen and this time rather than refill the compressed gas bottle I'd like to install a Hydrostik in its place. I have obtained all the fittings I need but have hit a snag! I need a few short pieces of 10mm OD 1 or 2mm wall stainless tubing to go into the Metric Swagelok fitting. However all I can find on the net would cost me over $100.00! Does anybody have a few short lengths (two 3" and two 4" if cut ready to insert in the fitting) or one 18" piece that I could buy at a reasonable price??? Thanks, Corby ___ 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] Need some wisdom from the cesium beam tube gurus out there
Skip, The easiest way to determine the oven resistor values for an unmarked tube is to directly measure the oven temperature and select a resistance to set it at the temperature you want. Your tube is a STD tube so I'd set it at 90 degrees C. Take a thermocouple meter and thermocouple and cut the junction off the end of the thermocouple. Attach a couple tiny alligator clips or grabbers. Next look at the potting around where the tubes cables come out. You should see short stubs of two different color wires peeking out of the potting. These are the ends of a thermocouple connected directly to the oven housing! I can't remember which type thermocouple it is. (I'll look in my notes and at the meter I use and let you know!) Connect the wires to your meter matching the color of the wires. Now with the tube cold you should see the ambient temperature on the meter. Power up the unit and you will see the temp start to rise. It will stabilize at the point determined by the resistance you selected. If too hot increase the resistance if too cold decrease. Cheers, Corby ___ 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] Corby Dawson Super 5065a work can I use a miniature Rubidium
Anton, To answer both questions: You can use a Laser in place of the Rubidium lamp, however assuming the problem is the lamp it would be cheaper to buy several LPRO units to scavenge for a replacement lamp. How did you determine it's the lamp that is dead? Using a Laser is more complicated than it sounds. The Laser frequency has to be stabilized at the proper wavelength. This usually requires a combination of selecting the proper diode current as well as the proper temperature. Even then the diode ages and drifts away from the proper spot. Sometimes a separate Rubidium vapor cell is used to stabilize the frequency of the diode. The equipment to run the diode would take up MUCH more room than the LPRO! This is why you don't find commercial Rubidiums using Laser diodes! (YET) The Super modification will not work on the miniature Rubidiums. (although some do filter the lamp to get a better SN, however performance is not anywhere near a Super.) The 5065A has a large cell and runs at a low temperature, this offers the ideal stability and the chance to Super it. Even so not all 5065A can be Supered! Cheers, Corby Dawson ___ 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] Rare HP clock
I have worked on these and the electronics is almost always working, or easily repaired. The mechanical can cause problems depending on how much "time" it has on the clock mechanics. No XTAL in these as the drive is external. The case is hermetic and has dessicant inside. Cheers, Corby Dawson ___ 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] COTS cesium standard physics package life
Ruslan, Yes you can conserve tube life my operating in the Cs off mode (for 5061A and B). This mode still powers the ion pump and helps maintain the vacuum. If the tube is exposed to high temperatures for a long period the Cesium will slowly escape the oven assy. and reduce the life of the tube. As long as a vacuum is maintained and the tube is not exposed to high temps you should still get the specified operational life of the tube. If the oven is off the life is not reduced. The main problem of long storage without occasionally powering the ion pump is that the pressure in the tube can rise above the starting pressure of the ion pump. In this case an external ion pump supply can help, however the pressure can get great enough that even that won't help! I usually recommend running in Cs off mode until needed and insure that once every 3 months you go back to operate and allow the unit to run for a few hours. Cheers, Corby ___ 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] Adjusting nominal frequency of FTS 1200-100 OCXO?
Christopher, The only way is to open the oscillator up and reselect the capacitor they used to set it on frequency. I've done it once or twice long ago, not easy to do! I have a 1200 with the same problem however it does tune to 1Hz low so I use it as the offset oscillator for my DMTD unit! Cheers, Corby ___ 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] HP 3010Axxxxx oscillator
Perry, The 3010A prefix identifies that date it was made. It should also have a 10811A marking. The resistor value is for applications needing precise EFC. Usually found in HP 5065A, 5061A, and 5061B. If it also has a 60109 marking it has slightly better short term stability at one Tau. Specs are otherwise the same as any 10811A. There is no outer oven! Since the design is a complete departure from the original 105 oscillator it makes sense they issued a new part ID. The 10811A started to go into the 105A and the 5061A and 5065A after the 105 style oscillator was discontinued. Cheers, Corby ___ 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] Some interesting HP5071A design information
Hi, I've had this booklet for quite a few years and whenever someone posts about the HP5071A I think of sharing it. Finally got around to scanning it and Tom VanBaak was kind enough to host it on his website. It's at http://leapsecond.com/corby/5071comb.pdf Enjoy! Corby Dawson ___ 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] More FE405B data
Hi, I posted an AD plot of a good FE405B back on Jun 7th. A plot just completed today after an additional month of running is essentially the same. I did however measure the aging rate and it is currently 1.15X10-11th per day! Cheers, Corby ___ 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] Spin exchange tuning
Ole, Spin exchange tuning for a classic (non-autotuned) Maser is performed to put the cavity to the frequency that corresponds to the point that eliminates the frequency shift caused by changes in the Hydrogen flux. This enhances the short term stability at short time scales. This tunes the cavity OFF of resonance by a small amount! The procedure is to plot the Maser frequency at a few different cavity tuning voltages at one pressure and repeat it for another pressure. Plotting these points against frequency gives you two lines that intersect at the spin exchange tuning point. You then set the cavity tuning voltage to correspond to that spot on the graph. There is a major problem in this however. You need a 2nd Maser as the reference source as you need 1X10-14th resolution at 100 Seconds! On the classic Maser you would repeat this at some interval, Months to years to maintain your tuning point. (some applications can get by without ever doing the Spin exchange tuning!) On an autotuned Maser you still need to determine the point and a corresponding offset to be applied to the servo circuit, once established the servo can be turned on to maintain the tuning at the correct point. (Just servoing the cavity to the peak of the response will NOT put you at the spin exchange tuning point! ) On the EFOS2 Maser that lives here I have never completed the spin exchange tuning. (No 2nd Maser!!!) However for the stuff I do, measuring AD of precision standards, the Maser has performed admirably for 9 years now. I have been planning to try a different method to do the spin exchange tuning that would not require the 2nd Maser. If it works out I will let you know. Cheers, Corby ___ 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] Anyone have an HP5060A sitting around?
Hi, I need a couple resistance readings at the A11 oven controller jack. Does anyone have one available that they could measure for me? Cheers, Corby ___ 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] HP5065A Super upgrade
Herbert, If you find my original post and also look at the HP5065B info on leapsecond. com you will find that the pre/post performance is closer to that listed below. I belive Luciano missread the plots! Cheers, Corby Dawson Typical ADEV improvement Seconds BeforeAfter 1 1.4x10-12 4x10-13 10 4.0x10-13 2.1x10-13 100 1.2x10-13 6.0x10-14 Note: C.Dawson measurements ___ 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] Some FE405B data
Attila, All oscillators are not the same! Although I find the yield to be better for the FE405B than say the 10811 some are duds like the top trace in Toms data, some are very good like the bottom trace, and some are even better, my plot. I've been very impressed by the 405B performance as I have run through testing a pile of them! Cheers, Corby ___ 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] Divide by 3
The FE405B AD plot I recently posted used a simple (non 50% duty cycle) divide by 3 using a 74ls74 and 74ls02 (if I remember correctly). I used the HP board from the pair used in the 5065A or 5061A/B. The existing 74ls74 was piggy backed with the 74ls02 and connections made with tiny wire. The non-symmetrical 5Mhz output of the divider went into the existing 5Mhz filter amp resulting in a nice clean Sine wave. As the plot shows the AD does not suffer using this simple scheme. Cheers, Corby ___ 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] THE Original Time Interval Counter
Well, This is probably not the original but I remember using one "in the day" Corby___ 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] Some FE405B data
Attached here is a long term AD plot of an FE405B. Stays in the 10-13ths all the way up to 10,000 seconds! This unit has only been operating for about 2 weeks. In a month I'll repeat this plot and also include the aging rate. I have found that these oscillators exhibit less drift than most others I have tested! Cheers, Corby Dawson___ 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] Goodie for British Timenuts!!!
Hi, Saw this while trolling for goodies! http://www.mullardmagic.co.uk/racal-ma259-frequency-standard-ra17-ra117-r af-navy-goldfinger-james-bond-ra1218-ra1772-ra1792-ma50-ra181 RACAL MA259 FREQUENCY STANDARD FROM 1965 Looks neat Cheers, Corby ___ 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] HP 106a oscillator connectors question
Thanks for all the info. They are the 1/4-32 (S-93 compatible) Microdot !!! I ordered a double ended cable and will cut it in half to give me the two connections I need (5Mhz out and EFC in). Cheers, Corby ___ 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] HP 106a oscillator connectors question
Well the checkout of the 106A oscillator section is going well. I ran it for 6 hours and the outer oven came down OK, will have to wait until I can do a longer attended run for the inner oven as it takes 8 1/2 hours per the manual to come down! This unit was not built with the fine adjust via an internal pot as shown in the manual but does have the external EFC jack show. (EFC jack does work) After the 6 hours Frequency was within a HZ and could be adjusted. Quit there until I can find a spot for it to live for an extended test. Need help identifying the RF connectors on the unit. They are not SMA but look to be the same diameter. would need two adaptors or a couple old cables with the matching connector I could splice into. I had to poke in a wire and use clip leads! Cheers, Corby___ 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] Mystery hp Ovens For Sale
Got an email from someone who has the main unit! Found out that the assy. is from an O-451A/U. Possibly coast guard. It is supposedly a double ovened unit. Does anyone have any info on it? Cheers, Corby ___ 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] Mystery hp Ovens For Sale
Peter, Thanks for the heads up! I purchased both units and they arrived yesterday. I was worried for a moment as the HP106 assy. also had an HP107 part number on a label on the side. I realized that it was too big in diameter to fit a 107 but wonder why HP put that label on it??? Carefully disassembled it and everything looked very nice inside including the giant Bliley 2.5Mhz XTAL. I had to clean off a bit of cadmium "fungus" off a few of the mechanical mounting parts. Also there are 3 of the old style white Vitromon capacitors in the oscillator section. These caps had tin whiskers "crowns" covering each end! They were removed easily with a small stiff brush. Now to apply some 24VDC and see if it fires up! The other unit has no identifying information, the two end caps come off by pushing three locking slides over and pulling. Inside the adjustment end there is a small (7 or 9) pin electron tube! The oven end construction reminds me of a General Radio oven I one worked on. Built like a battleship! Anyone have any idea what it might come from. I'll try and post a PIX later. Might be 100Khz or 1Mhz. Cheers, Corby ___ 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] HP5065A environmental sensitivities
Angus, The M100 barometric data data is attached, the FRK should be the same. Not sure what the time constant would be however. So those units at least should have repeatable performance as far as Barometric pressure is concerned. Not sure about any of the other smaller units. Cheers, Corby___ 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] HP5065A environmental sensitivities
Angus, The HP 5065A has a fairly open path from atmosphere to the cells as far a barometric pressure is concerned. Response is rapid to a change. The mechanism is "oil-canning" of the windows on the ends of the cell. Depends on diameter of the cell, thickness of the windows, and stiffness of the particular glass used. (for a particular gas mix of course) It is VERY repeatable, and VERY linear. I have heard that one European observatory routinely tracks the barometric pressure by watching their 5065A shift. After seeing Wulf's data I can believe it! My circuit is eliminating that variable quite nicely. As others have said, temperature will be a different matter. I'm currently doing temperature tests and plan to eliminate the major causes rather than compensate. Early measurements show as-built to be better than the spec of 1.6X10-12/degree C. Cheers, Corby ___ 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] HP5065A environmental sensitivities
Nice data Wulf. Once I finish reducing the temp effects I'll post a couple long term AD plots with and without the Barometric pressure compensation and with and without the temperature modifications. Will be interesting to see what kind of difference I get. Cheers, Corby ___ 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] HP5065A environmental sensitivities
Luciano. Hi, 1) it is difficult to read the frequency value on the plot. Can you specify? The plot is averaged to get the signal out of the noise, The P-P calibration offset on the left allows you to estimate the deviation of the other parts of the plot. The short term stability of the 5065A at 1 sec is causing the noise you see. 2) how do you set the offset of the op-amp trimmer ? The trimmer is set for zero out of the op-amp at ambient pressure, this allows the output to be plus/minus, not critical just zero it after you install it. 3) do you think is possible to use the -20V on the HP5065A instead the -12V from the DC-DC converter? Probably would work fine as the load on the minus side is just the op amp. 4) what frequency measurement system do you use? The maser is input to one side of a DMTD unit, the 5065A at about a .5Hz offset via the A1 synthesizer is input to the common oscillator input of the DMTD. This setup give a SMTD configuration. A ping-pong counter then feeds a laptop. A good quartz can be used instead of the Maser but WILL show up as drift in the plot. I am curious to know how you have generate the barometric swing. Put the 5065A in a sealed box (easy to say hard to make work!), zero the op-amp, run pressure up to .5PSI (-160mv at op-amp), then when done reverse pump and pump down to -.5PSI (+160mv at op-amp). When done remove pump and go back to ambient pressure. (I used a 12 Volt pump used to inflate/deflate an inflatable bed, also used a variable supply into the pump to allow setting the pressure/vacuum) The box I made has a LARGE two sided heat sink on the lid, one heat sink goes down into the box and the other is outside. This allowed me to keep the 5065A at around 44 degrees C during the tests. (box stayed sealed for a couple weeks while I generated data.) This box will also be used for the temperature testing. The SBT R7 resistor is used to set the P-P current change generated by the +-160mv output to match the P-P frequency excursion caused by the same. Being of opposite polarities they will then cancel out any barometric changes. Cheers, Corby ___ 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] HP5065A environmental sensitivities
HP 5065A Environmental sensitivity First here is a comparison between the specified sensitivities of various Rubidium units. Barometric per mbar Temperature per degree C HP 5065A6.3X10-14 1.6X10-12 M100 FRK 8.7x10-14 2.4X10-12 LPRO1.0X10-13 6.0X10-12 FE5650A unspecified 1.1X10-11 FRSC1.0X10-13 1.1X10-11 PRS10unspecified1.0X10-11 As you can see the HP specs are better than the others! After much effort I managed to measure the actual sensitivity of a 5065A on my bench. It was much better than the spec at 1.55X10-14/mbar! I then installed a barometric compensation circuit consisting of a sensor and OP amp. This feeds the C-field circuit in the 5065A. After alignment the sensitivity was so low that it was below my measurement noise floor! Attached is a frequency plot that illustrates the correction. On the left is a calibration offset from the Maser of plus/minus 1.84X10-12. The middle section shows the frequency with the compensation on during several cycles of plus/minus 35 mbar. The right is with compensation off and the plus/minus 35mbar excursions. Also attached is a schematic of the compensation circuitry. Now I'll work on the temperature sensitivity. Poul-Henning has explored in this area and has some good information to start with. Cheers, Corby___ 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] HP 5360A History?
The oscillator used in the 5360A is the same one used in the early 105A, the 5061A and the 5065A. I just call them the 105 style oscillator. They have a 115 volt thermoswitch controlled fast warmup heater that is set to switch out once it gets close to the set point of the proportional controller oven that stays on all the time. 10811A units are better performers. Cheers, Corby ___ 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] HP 5065A repair
I'm changing the topic from best rubidium frequency standard for this post. Most repairs I make to the 5065A run well below $250.00, sometimes as low as $100.00. A "crazy bad" repair might run $400.00 or so but out of over 50 repairs only two needed that level of help. As far a tempco goes, unless your lab swings tens of degrees will you really see it? Short term stability scales with cell size and is also proportional to the design temperature. Also separate filter and resonance cells perform better than an "integrated" cell. The 5065A cell is the largest available today and the 66 degree C is the lowest temp around these days. The 5065A cell also has a temperature regulated stem to stabilize the Rubidium level. These combine to give a typical STS of 1.5X10-13 at a Tau of 100 Seconds. Unfortunately as others have noted, it is easily the most expensive Rubidium standard out there. A few members are looking into improving the tempco and I hope testing the barometric pressure performance. Cheers, Corby ___ 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.
