10MHz standard to drive Counter and SA - Page 1
Forum section: electronics / testgear

author: Jester
author_rank: Frequent Contributor
timestamp: December 12, 2016, 03:23:26 am
content: I'm looking for frequency accuracy. If you had to choose between these two, which one would you choose, I like the simplicity of the Rubidium, not keen on punching a hole through the wall for an antenna:1)http://www.ebay.com/itm/291965740516?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT2)http://www.ebay.com/itm/Used-10MHz-Trimble-65256-GPS-OCXO-Precision-Clock-circuit-board-oscillator-/142203985287?hash=item211c049d87:g:rKgAAOSwZjhXIsw2#2 does not have any information regarding power, UART connection etc, in the listing and I'm not sure if the required information is readily available?

author: edpalmer42
author_rank: Super Contributor
timestamp: December 12, 2016, 04:23:01 am
content: You haven't said how accurate you want the frequency to be. 1 PPM? 1 PPB? 1 PPT? The Rb might be good enough out of the box that you will never need to even check it, never mind adjust it. Or, you might need to tweak it to get it on frequency and then forget about it. Most Rb units have a typical monthly drift in the range of 5e-11 per month. Look at your application and do the calculation to see if that's good enough. If not, a GPSDO like your second item might be the answer.But the question isn't quite that simple. If you happen to have a need for really good phase noise or really good short term jitter, you might find that neither solution is adequate. For that situation, nothing beats a good quartz OCXO.The Trimble GPSDO is known here on eevblog. There's enough info here and on the Time-Nuts mailing list that you shouldn't have any problem setting it up. Actually, I've got one running on my bench right now. I've just added it to my performance list below.Code:[GPS Devices -- Measure & analyze the period of the 1 PPS OutputDevice ............... Std Dev (ns).... Range (max-min)(ns) ... Device ...... NotesNavsync CW12 ......... 4 - 5 .......... 20 - 25 ............... GPS Rcvr .... 1,7Motorola UT+ ......... 40 - 55 ........ 95 - 110 .............. GPS Rcvr .... 2,7Rockwell Jupiter ..... 10 ............ 50 ................... GPS Rcvr .... 3,7Motorola M12M ........ 10 - 15 ........ 40 - 60 ............... GPS Rcvr .... 7Trimble Thunderbolt .. 0.4 - 0.5 ...... 2 - 4 ................. GPSDO ....... 6,8HP Z3801A ............ 0.1 - 0.2 ...... < 1 ................... GPSDO ....... 6HP Z3817A / CW12 ..... < 0.1 .......... < 1 ................... GPSDO ....... 4,6Jackson Labs GPSTCXO . 0.3 - 0.4 ...... 2 - 3 ................. GPSDO ....... 6NEC NWM-034241-201 ... 0.1 - 0.2 ...... < 2 ................... GPSDO ....... 5Trimble UCCM ......... 0.09 - 0.11 .... < 1 ................... GPSDO ....... 5Results are based on multiple runs of ~ 1000 measurements each.Sawtooth correction has not been used for any of the GPS receivers. Where supported, it would reduce the numbers substantially.All units were connected to the same antenna system.Notes1. Sawtooth correction not supported.2. Most 'range' results were in this group, but there were a few at 20 - 30.3. Only one test.4. Requires external 1 PPS input. Equipped with E1938 oscillator.5. Measurement made with Fluke PM6681.6. Measurement made with HP 5370B.7. Measurement made with HP 5372A.8. Standard parameters.9. Optimized parameters. (Not yet used in any tests)It appears to be pretty good, based on these measurements.FYI, usually, you don't use Standard Deviation to evaluate the performance of an oscillator. The drift causes massive problems in the calculations. But in a GPSDO, the drift is cancelled out so AFAIK, the use is valid.The answer that works for me is to have a Rb standard as my house standard. I distribute it to my test equipment and use it as a frequency reference for tests as required. I also have a, well actually two, GPSDOs that I occasionally compare to the Rb to measure the Rb's drift. For measurements that require good short-term jitter, I have a few good OCXOs.By the way, you should be aware that particular Rb unit is a Chinese model that AFAIK, hasn't been evaluated or reported on here or on Time-Nuts. There may be something on one of the Chinese language boards. Knowledge and support on that unit will be limited. It's similar to the LPRO-101, but may have some different or extra features. I see that it has RS232 connections unlike the LPRO. YMMV.Ed

author: CJay
author_rank: Super Contributor
timestamp: December 12, 2016, 12:06:18 pm
content: If I were buying a Rb standard on eBay I'd be considering the FEI from Fluke.I instead of the Chinese one, in fact they've got an pption 58 FEI 5650 listed on a BIN for less than the Chinese one, should be plenty good enough once tested and checked against a good standard.

author: Jester
author_rank: Frequent Contributor
timestamp: December 16, 2016, 02:33:02 pm
content: Quote from: CJay on December 12, 2016, 12:06:18 pmAfter some searching I found some answers so I'm updating this entryThe datasheet I found does not describe option 58?option 58 = 1pps outputThe ad states that this device would need to be set to 10MHz. From what I have read the internal DDS chip can be reprogrammed to make it 10MHz. I also read that when changing the output frequency that the output filter needs to be modified to match the new output frequency.Should I expect to see a sinewave or square wave from the option 58 5650?a sinewaveAny insight on the filter changes required?I guess I will see what the waveform looks like when reprogrammed to 10.0MHz, 10MHz is a long way from 1Hz!