[time-nuts] Another use for a Trimble Thunderbolt
’d say that the plot is telling the truth. It also seems to be giving you information fast enough that thermal drift and barometric pressure is not to big an issue. If you had to wait a day or three for the same data, drift would be a much bigger issue. Yes, when you get to the “close enough” trace, drift may be an issue. (yes close enough is indeed close enough …). Keep in mind that I'm talking about using a GPS signal from a Thunderbolt to adjust a common rubidium standard that would be used in a telco or other piece of general test equipment and thermal drift and barometric pressure effects are never an issue for me. I suspect that if you try the trick with something way far off frequency (many 10’s of ppm), the GPS may not play nice. At any normal tune range on an Rb, it should be fine. Actually it does play nice-very nice over any range I'm interested in. Keep in mind that I wanted a simple method that would work with a 10 Mhz frequency standard to give me closer readings than I could get by watching the scope or the counter. I can easily use just the counter to check the frequency of a less than stellar oscillator so what I'm describing would be used with a fairly close 10 Mhz frequency standard and not one that isn't even close. The Pendulum CNT-81 frequency counter I have can display a 10 Mhz error to 5 decimal places in 10 seconds using the math function and an external time base. Anyone who has used a WWVB comparator remembers the plot zipping back to the zero position when the plotted frequency difference would exceed the chart's maximum deflection. The Thunderbolt's display on Lady Heather works exactly the same way. If you look at the plots in the link that follows you will see that the 10 Mhz appears very stable but it is actually set by a synthesizer to be 10,000,000.025000 hz in the upper trace and so to keep it in the vertical center position on the graph I have an oscillator offset of -2500 PPT in Lady Heather. In the lower trace the synthesizer frequency is set to 10,000,000.010 hz and the offset is -1000 PPT to keep the 10 Mhz trace centered. The reference for the synthesizer and the Thunderbolt is the GPS signal from the Tbolt so the same reference is used for everything. http://s906.photobucket.com/user/rjb1998/media/tboltplots_zpsd20a083b.jpg.html -Arthur ___ 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] Another use for a Trimble Thunderbolt
On Dec 25, 2014, at 8:11 PM, Arthur Dent golgarfrinc...@gmail.com wrote: ’d say that the plot is telling the truth. It also seems to be giving you information fast enough that thermal drift and barometric pressure is not to big an issue. If you had to wait a day or three for the same data, drift would be a much bigger issue. Yes, when you get to the “close enough” trace, drift may be an issue. (yes close enough is indeed close enough …). Keep in mind that I'm talking about using a GPS signal from a Thunderbolt to adjust a common rubidium standard that would be used in a telco or other piece of general test equipment and thermal drift and barometric pressure effects are never an issue for me. Your 15 ns / hour limit comes out to ~ 4.12 x10^-12. Your “close enough” comes out (eyeball @ 1/4 slope) to 1x10^-12. If your Rb has a tempco of +/- 2x10^-10 over 100 C that *might* be 4x10^-12 / C. If your room moves +/-2 C per hour (as some do) temperature could be an issue. You would be seeing 1.6x10^-11 cycles under those conditions. In order to reasonably “see” your 1x10^-12 limit, the setup you are running would have to be at least 10X better. At that point temperature rather than set point would dominate the plot. In order to measure set point, you would need 100X better. Are all Rb’s “worst case?”, of course not. Are they all polite and straight line linear over the entire range? - not on the ones I’ve seen. Throw in things like a draft on the heat sink when the HVAC fires up …. — This is *not* in any way a knock on the approach. It seems to work very well for what you are trying to do. It’s well though out and functional. It’s simply a caution that drift can be an issue doing this sort of thing to the 1x10^-12 level on Telco Rb’s. Bob I suspect that if you try the trick with something way far off frequency (many 10’s of ppm), the GPS may not play nice. At any normal tune range on an Rb, it should be fine. Actually it does play nice-very nice over any range I'm interested in. Keep in mind that I wanted a simple method that would work with a 10 Mhz frequency standard to give me closer readings than I could get by watching the scope or the counter. I can easily use just the counter to check the frequency of a less than stellar oscillator so what I'm describing would be used with a fairly close 10 Mhz frequency standard and not one that isn't even close. The Pendulum CNT-81 frequency counter I have can display a 10 Mhz error to 5 decimal places in 10 seconds using the math function and an external time base. Anyone who has used a WWVB comparator remembers the plot zipping back to the zero position when the plotted frequency difference would exceed the chart's maximum deflection. The Thunderbolt's display on Lady Heather works exactly the same way. If you look at the plots in the link that follows you will see that the 10 Mhz appears very stable but it is actually set by a synthesizer to be 10,000,000.025000 hz in the upper trace and so to keep it in the vertical center position on the graph I have an oscillator offset of -2500 PPT in Lady Heather. In the lower trace the synthesizer frequency is set to 10,000,000.010 hz and the offset is -1000 PPT to keep the 10 Mhz trace centered. The reference for the synthesizer and the Thunderbolt is the GPS signal from the Tbolt so the same reference is used for everything. http://s906.photobucket.com/user/rjb1998/media/tboltplots_zpsd20a083b.jpg.html -Arthur ___ 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] 10MHz LTE-Lite
I had PCBs made by OSHPark for the buffer discussed below. I just built one up and it's working fine. 3 outputs giving about 10 dBm each. The board design is shared at: https://oshpark.com/shared_projects/pCpmILwj There are links to the schematic and a picture of the mostly complete board. If you have SMA end-launch sockets, they may fit the board (I'd have to scrape some solder mask off the ground plane for the ones I have to fit) or you can just solder coax directly. Use the pads on the bottom of the board for the coax screen. Feel free to use the design. (If you sell anything based off it, please attribute the source.) Orin. On Sat, Dec 6, 2014 at 10:32 PM, Orin Eman orin.e...@gmail.com wrote: Hi Said, It's a little while since you sent this, but I just finished some testing with the LTE Lite. I already had a Trimble Thunderbolt and also have an HP 5335A with OCXO. The 5335A has shown the Trimble O/P 10 MHz +/- 0.03 Hz for the last few years (displayed frequency on the 5335A has drifted down by about 0.04 Hz). So, I set up the LTE Lite (10MHz TCXO version) with its antenna about 6' from that used by the Trimble. After letting it settle down, it looked good. I was using the high impedance input of the 5335A (aside: if set for DC coupling, the 5335A would read 20MHz from the ringing. I only have about 18 of RG-188 after the pigtail supplied with the LTE Lite). Today, I made up a buffer using a 74AC04 and LT1763-3.3 LDO regulator supplied with 5V from a bench supply. Two inverters each into 100 ohms then 0.1uF DC block as suggested. I connected this to the LTE Lite instead of directly to the 5335A with the 5335A set to 50 ohms and the 5335A read 0.5Hz low! It settled down to the original reading after a while. I looked at the signal from the buffer using a 50 ohm pass-through terminator and the signal looked nice and square. A few hours later I went back and it still looked good. I decided to look at the input to the buffer on a TDS-210 'scope with a 10X probe. There is now perhaps 6 of coax to the buffer which has 1 Mohm in parallel. The signal is about 5V pk-pk, but the ringing dies down quickly. BUT, the 5335A was displaying a few hundredths of a Hz higher than 10MHz, whereas it was a few hundredths below before! When I removed the probe, it went a few hundredths of a Hz below where it was originally and gradually recovered. So, in addition to temperature, the LTE-Lite eval board with 10MHz TCXO appears to be sensitive to load as well as temperature, such that just a 10X oscilloscope probe will affect the output. Normally, you probably wouldn't notice this, but I switched the loads while it was running. Certainly, once put in an enclosure, the 74AC04 buffer would be permanently connected and I'd assume any effect noticed above would be during the warmup of the LTE-Lite and wouldn't really be noticed. I'm sure I forgot some detail or other in the above description. I couldn't find a DIP 74AC04 so I made a PCB for an SMT 784AC04 using MG Chemicals 1/32 positive-resist PCB and Eagle for the design; 1206 100 ohm series resistors and 1206 0.1uF ceramic DC blocking capacitors. I laid it out for SMA sockets that you could wire RG-316 or similar directly instead. I used a 6 MMCX to RG-316 pigtail from the LTE-Lite to my buffer. I mounted one SMA socket on the outputs which is what I used to connect to the HP 5335A. The LT1763 has a 1uF 35V tantalum on the input and 10 uF 30V tantalum on the output (they are what I had in the parts bin, or I'd have used *smaller* ceramic parts). I tweaked the design for hand soldering with no solder mask (i.e. 20 mil clearances and top layer restrictions around most components to keep the ground fill away). Orin. On Sat, Nov 22, 2014 at 9:44 AM, Said Jackson via time-nuts time-nuts@febo.com wrote: Hi Paul, Jim, David, Let me address all your emails: Glad you got your boards. $50 in overseas additional charges from your post office sucks! Some hints for experimenting from what I have learned: You definitely want to build a 50 Ohms buffer for the 10MHz boards and the synthesized outputs on all boards; on the 20MHz boards on the Tcxo output it's optional. The biggest problem is building a suitable 3.3V or 5V power supply. I built a buffer using two NC7SZ04 chips receiving the input in parallel with a 1M terminating resistor to ground. Then using a 100 Ohms series resistor on both outputs to get ~55 Ohms equivalent impedance, and combining the two R's to drive the 50 Ohms inputs through a 100nF cap for DC blocking. You can use a 74AC04 just as well. I tried a standard high quality 3-pin regulator and got very bad AM noise modulation due to the large noise on the rail. Then I used a very low noise LDO from LT and that solved the problem and the output is now very clean and drives 50 Ohms inputs with ease. you can grab the very low noise 3.0V rail output from the eval
