Re: [time-nuts] LTE-Lite module and the pendulum...
Burt, Great insight thanks. You nailed it: out with the old oscillator and in with one that doesn't have that problem. Btw the mechanical tuning issue you mentioned is essentially the same exact problem: even the slightest turn will make the frequency jump too high or too low. It can drive you (and the loop) crazy trying to get it on-frequency. Bye, Said Sent From iPhone On Oct 21, 2014, at 8:54, Burt I. Weiner b...@att.net wrote: I've been following this thread with some interest. I have no idea what a LTE-Lite module is, but I believe the issues being discussed is essentially the same issue that I had a year or so ago when I had to make repairs to my two DATUM 9390-52054 GPS references. At that time I copied this list on the various steps from discovery of the power supply noise grief to further discovery of problems with the original factory supplied internal Vectron VCXO oscillator module. After replacing the internal switching power supply with an outboard Cisco unit, I went on to look at what I felt was instability of the 10 MHz reference. According to the front panel display, the error would wander anywhere from 0E-12 to 50 or 100E-12. For my use, this wasn't a major problem, but one that bothered my instinctive curiosity and another step in my life in searching for a way to improve things. The original oscillator module in the 9390 was a Vectron 716Y2690. This has a frequency trim adjustment on the side to bring the oscillator into tracking range for the DATUM 9390. In one of my two units the adjustment would jump, which I attributed to a defective trimming capacitor. My friend Stu, K6YAZ had previously given me two McCoy MC597X4 VCXO modules that do not have a frequency adjustment other than by way of the EFC control. Looking at the specs on these modules it looked like they might almost be electrically a drop in replacement for the original Vectron modules, although the McCoy's were about one-quarter the size. The McCoy's require 5 volts Vcc rather than 12 volts that the Vectron required. Not a problem. Testing confirmed that the EFC tuning voltage indeed went the same direction the McCoy requires. Since I don't have the sophisticated equipment that many of you have to comparatively confirm stability, I decided to modify only one of my 9390's and compare the results to the other one. The two 9390's have separate antennas mounted about 3 feet apart and in a pretty clear view of the sky. I stuffed the McCoy module in place of the Vectron but instead of connecting the EFC lead, I used a 1k pot with the top connected to 5 volts through a small resistor, the bottom to ground, and the arm to the EFC pin on the McCoy. Using the other 9390 for comparison, I was able to determine that in order to have the McCoy output 10 MHz, the EFC voltage wanted to be slightly under +4 volts, essentially the same as the original Vectron. Great, what could go wrong? I shut everything down and connected the EFC control voltage to the EFC terminal on the McCoy. As the McCoy came up to temperature I got a tracking light and the 10 MHz spigot came nicely onto 10 MHz, sat there and then wandered off frequency and after a while came back and overshot in the other direction. I figured this would be a process that would go on for a day or two and the pendulum would eventually settle in. After several days this did not happen and the 9390 gave me a tracking error. Apparently, the time co nstants in the loop and the sensitivity of the EFC control in the McCoy did not play well together. Pondering the situation I decided to slow down the EFC voltage change. I did this by putting a 4.7 uf capacitor across the EFC pin to the ground pin and fed the EFC voltage to the EFC pin through a 5100 Ohm resistor, essentially, in my opinion, hanging a flywheel across the EFC line to the McCoy. Since with the smaller McCoy I had additional space within the 9390 I also made a sandwich type enclosure out of foam for the smaller McCoy to help isolate it from tempreture changes. I let the unit run for about 24 hours and noted that it had settled in nicely and sat, according to its display, at 0E-12 for well over the next 24 hours. Comparing this to my stock 9390, this appeared to be correct except for some small amount of wandering - the stock unit was showing variations of 1E-12 to about 10E-12, the amount of drift they had both always shown. I watched this for about two weeks an d while the modified 9390 sat at 0E-12, the stock unit continued to show the same amount of drift it always had shown. I modified my second 9390 with the other McCoy VCXO and now the two units sit within 0 to 1E10-12, and comparing the two using both a 1:1 Lissajou and separately using one to trigger a scope that's monitoring the other, I believe things are much improved. In the year plus since I've modified these two units
Re: [time-nuts] LTE-Lite module and the pendulum...
Great insight thanks. You nailed it: out with the old oscillator and in with one that doesn't have that problem. Btw the mechanical tuning issue you mentioned is essentially the same exact problem: even the slightest turn will make the frequency jump too high or too low. It can drive you (and the loop) crazy trying to get it on-frequency. Whenever I've seen this behavior, it has always been caused by uncertainty or quantization on the part of the trimpot's wiper, rather than anything that could be blamed on the varactor. What would be a good example of a TCXO or OCXO model that exhibits EFC hysteresis? I don't immediately understand what could cause this phenomenon, and I'd like to reproduce it here to see what's happening. -- john, KE5FX Miles Design LLC ___ 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] LTE-Lite module and the pendulum...
Hi John, while I can't tell you which vendors are affected and which are not (Its like asking an angler for his secret angling spot :), I can say that most low cost TCXOs exhibit this behavior, and are thus not really suitable for GPSDOs. The ones we used on the LTE-Lite are quite good and do not exhibit this behavior. They are also 10x more expensive than the lost cost TCXOs in the exact same package that are typically used in non-critical applications. So far none of the quite reputable TCXO and OCXO vendors that I contacted about the problem can explain the behavior to me, like I said they were not even aware of the issue and had no way to test for it, and I had to prove it to them by sending our units to them so they can see the issue for themselves. Bye, Said In a message dated 10/21/2014 11:51:28 Pacific Daylight Time, j...@miles.io writes: Great insight thanks. You nailed it: out with the old oscillator and in with one that doesn't have that problem. Btw the mechanical tuning issue you mentioned is essentially the same exact problem: even the slightest turn will make the frequency jump too high or too low. It can drive you (and the loop) crazy trying to get it on-frequency. Whenever I've seen this behavior, it has always been caused by uncertainty or quantization on the part of the trimpot's wiper, rather than anything that could be blamed on the varactor. What would be a good example of a TCXO or OCXO model that exhibits EFC hysteresis? I don't immediately understand what could cause this phenomenon, and I'd like to reproduce it here to see what's happening. -- john, KE5FX Miles Design LLC ___ 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] LTE-Lite module and the pendulum...
Also have this problem with capacitor-adjusted tuning. No matterhow careful you turn, stiction causes the adjustment to jump in the direction of the turn. Don John Miles Great insight thanks. You nailed it: out with the old oscillator and in with one that doesn't have that problem. Btw the mechanical tuning issue you mentioned is essentially the same exact problem: even the slightest turn will make the frequency jump too high or too low. It can drive you (and the loop) crazy trying to get it on-frequency. Whenever I've seen this behavior, it has always been caused by uncertainty or quantization on the part of the trimpot's wiper, rather than anything that could be blamed on the varactor. What would be a good example of a TCXO or OCXO model that exhibits EFC hysteresis? I don't immediately understand what could cause this phenomenon, and I'd like to reproduce it here to see what's happening. -- john, KE5FX Miles Design LLC ___ 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. -- The power of accurate observation is commonly called cynicism by those who have not got it. -George Bernard Shaw Dr. Don Latham AJ7LL Six Mile Systems LLC 17850 Six Mile Road Huson, MT, 59846 mail: POBox 404 Frenchtown MT 59834-0404 VOX 406-626-4304 Skype: buffler2 www.lightningforensics.com www.sixmilesystems.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] LTE-Lite module and the pendulum...
Burt, those old Vectrons can be tricky. I had a 100MHz unit in my DTS-2070 and it could not be adjusted to 100MHz anymore, it had out-aged its trim capacitor. I threw it away I think, and replaced it with something more modern. My initial point was that your trim cap problem is very similar to what the loop is experiencing on oscillators that have an EFC hysteresis. There is not a single vendor in the world that I know of that specifies this EFC hysterisis, and this and the retrace of the crystal over the first couple of hours are two extremely important parameters as they can cause significant errors in GPSDOs. bye, Said In a message dated 10/21/2014 15:10:09 Pacific Daylight Time, b...@att.net writes: Said, The DATUM 9390's I have came from the Sieko pager watch project that I was involved in back in the mid to late 90's. As I recall, even when the DATUM clocks were new we'd have to adjust the oscillators periodically to keep them within lock range. The center of the DAC was around 27000 and they'd wander about 1 plus or minus. They'd sometimes wander out of lock at plus or minus about 15000 and one of us would have to make a trip to some transmitter site to re-set the clock and re-center the Vectron module. The adjustment was accessible through a hole in the back of the clock. As I recall, you could give the oscillator a half turn one way or the other without causing too much distress to the clock. This held true with my two units until the one oscillator developed the adjustment problem. Not knowing what was really inside the Vectron, I attributed the problem to a defective or cracked piston capacitor. The adjustment certainly had the feel of a piston capacitor. Since I made the modifications I described, the DAC sits within about 10 of 27450, and that's where my units are happy. By the way, I've got two 1.5 KVA UPS's in my shoppe, one for each clock. They'll run for a long time on those. Burt From: Said Jackson saidj...@aol.com Subject: Re: [time-nuts] LTE-Lite module and the pendulum... Burt, Great insight thanks. You nailed it: out with the old oscillator and in with one that doesn't have that problem. Btw the mechanical tuning issue you mentioned is essentially the same exact problem: even the slightest turn will make the frequency jump too high or too low. It can drive you (and the loop) crazy trying to get it on-frequency. Bye, Said Burt I. Weiner Associates Broadcast Technical Services Glendale, California U.S.A. b...@att.net www.biwa.cc K6OQK ___ 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] LTE-Lite module and the pendulum...
Hi Depending on how much you spend on a mechanical piston trimmer, the innards will be coaxial to some tolerance. To the extent they rotate or “swing” as one piece moves in and out of the other, the capacitance will be more linear or less linear vs rotation of the trimmer. What you want - a straight line capacitance vs screw turns. What you get - a bit of a wiggly line of capacitance vs screw turns. On one side of the wiggle, the adjustment moves a bit fast. On the other side of the wiggle, the adjustment moves a bit slow. Next up is backlash. This a common issue in many mechanical systems. It’s most apparent in trimmers where a screw drives a moving part rather than the whole moving end being threaded. As the threads wear, they get a little slop in them Turn the screw clockwise all the time and everything is linear. Stop with clockwise and go counterclockwise and the threads have to mate no the other side of the screw. You don’t have anything happening until they do. If you read up on running a mechanical milling machine, you will see a lot of talk about this in terms of precision milling. Then of course you have broken trimmers. Ceramic trimmers can have the metabolized portions “stick” to each other. When you force them to move, you tear the metal off of the ceramic. Now you have a broken trimmer that really does odd things. Piston trimmers can get crud in them (either from outside or from their own moving parts). It does not take a very big chunk of stuff to short out the trimmer (if it’s conductive) or to mess up the tuning (if it’s not). Trim pots have their issues as well. The wipers can build up a bit of resistance from sitting in one place for a while. Move the trimmer and you clean up the contact. Depending on the circuit, this may or may not have much effect on the EFC to the varicap. Since trimmers can get a bit of force exerted on them, all the usual broken solder joint and ripped off the board sort of stuff applies to them as well. Lots of fun !! Bob On Oct 21, 2014, at 2:50 PM, John Miles j...@miles.io wrote: Great insight thanks. You nailed it: out with the old oscillator and in with one that doesn't have that problem. Btw the mechanical tuning issue you mentioned is essentially the same exact problem: even the slightest turn will make the frequency jump too high or too low. It can drive you (and the loop) crazy trying to get it on-frequency. Whenever I've seen this behavior, it has always been caused by uncertainty or quantization on the part of the trimpot's wiper, rather than anything that could be blamed on the varactor. What would be a good example of a TCXO or OCXO model that exhibits EFC hysteresis? I don't immediately understand what could cause this phenomenon, and I'd like to reproduce it here to see what's happening. -- john, KE5FX Miles Design LLC ___ 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.
