Lucent REF0 fault led on

[trevwhite]

Hi all.

I have a Lucent REF0 unit. I read info online about that you have to power it up and then after some time the fault led will go out. This 'some time' should be the time it takes the OXCO to stabalise. I have left the unit on for a few hours and still the fault led is on. Wondered if anyone had some experience with these? Maybe there are more things I need to do with it to get the fault light to turn off?

Trev

[4thDoctorWhoFan]

Well, I have a Lucent RFG-M-RB and the fault led will remain lit until the RB locks.  The fault led will then go out.
My unit takes about 5 to 10 minutes before the fault led goes out.  The unit need 24V power.

[ArthurDent]

4thDoctorWhoFan - If you check I think you will find that when the RFG is powered up the “TP” connector will have a square wave output and if you monitor this signal you will see it takes about 4 minutes for the Efratom rubidium oscillator to lock. Until the RFG locks this frequency output is not stable. About 3 minutes or so after the Rb oscillator locks, the red “FAULT” LED will go out and the green “ON” LED will light. At this time the 15Mhz sine wave output will be enabled. This is a well buffered, amplified, and filtered signal. Internally connecting the 10Mhz signal to this amplifier instead of the 15Mhz signal gives a highly accurate 10Mhz sine wave standard that can drive 50 ohms. Adding a 10-turn pot to the front panel will allow you to calibrate this unit against a GPSDO or other superior standard..

[ArthurDent]

trevwhite – The RFTG-u REF 0 isn’t designed to be a standalone unit and requires the REF 1 unit with interconnect cables or extensive modifications to work properly. Here is a photo of a modified unit that is a complete GPSDO. The power supply is mounted on the back and  on the left back side you can see the cable for the added GPS receiver. The BNC on the front right is for the buffered filtered 10Mhz amp to drive 50 ohms. The 10Mhz square wave on 'TP' isn’t that clean.

[trevwhite]

Hi all

I created a plugin board to simulate the GPS data as instructed in the below link. But I did not wire all the gnd pins of the J5 connector. If I wired up as per the following website told me in the first place it would help!

Corrected the J5 connector with all gnd connections soldered and fault led has gone off. Now I just need to see if I can get the NO GPS led to turn off.

YES! It just turned off as I was writing this message. Seems its all working fine now. Thanks


http://syncchannel.blogspot.co.uk/2015/08/standalone-operation-of-lucent-ks-24361.html

Trev

[ArthurDent]

Glad you got it working. I didn't know from your initial post that you had used the referenced article to make it think everything was working as it should. Sometimes missing one small detail (or wire) will set us scratching our heads until we notice our oversight.

The way I had chosen to go was to use the Motorola receiver so the REF 0 was completely self contained. If left on it is an excellent GPSDO and compares to other GPSDOs that I use. The first of these units I modified in 2011 was a REF 1 that was easier because it already had the receiver installed and all the jumpers in the correct positions. The MTI 260 oscillator used in these units is really nice.   

[4thDoctorWhoFan]

4thDoctorWhoFan - If you check I think you will find that when the RFG is powered up the “TP” connector will have a square wave output and if you monitor this signal you will see it takes about 4 minutes for the Efratom rubidium oscillator to lock. Until the RFG locks this frequency output is not stable. About 3 minutes or so after the Rb oscillator locks, the red “FAULT” LED will go out and the green “ON” LED will light. At this time the 15Mhz sine wave output will be enabled. This is a well buffered, amplified, and filtered signal. Internally connecting the 10Mhz signal to this amplifier instead of the 15Mhz signal gives a highly accurate 10Mhz sine wave standard that can drive 50 ohms. Adding a 10-turn pot to the front panel will allow you to calibrate this unit against a GPSDO or other superior standard..

A few questions:
Are you saying the 10Mhz output connector is not accurate?  Why would I want to internally connect the 10Mhz signal into the amp?  Why would I not just use the 10Mhz signal provided on the 10Mhz output connector? 

If there is a good reason for doing this, I'm all for it.  Are there any documents around showing how to do this internal modification?

Last question:  Isn't a RB more accurate than a GPSDO?  Why would I use a GPSDO to calibrate the RB?  Shouldn't it be the other way around?

Thanks,
Tony

[trevwhite]

Well my next question is how do I know just how accurate the 10Mhz output of the REF0 is? I have a PM6666 counter and I am looking to plug this 10Mhz into the extern ref input of the counter. If I do that I would then like to be able to measure other crystals. It seems if I measure for 10 seconds I can get a resolution on the counter of 10ppb which is just amazing!

What I would also like to do is measure stabiliy of some oxco. I think this is a whole different ball game but what equipment do I need to measure stabiliy of an oxco?

[ArthurDent]

4thDoctorWhoFan – When it is first powered on and until a rubidium oscillator locks, the frequency will wildly swing back and forth 100s of Hz. All the frequency outputs are derived from the same Rb oscillator. Once the Rb oscillator locks the frequency continues to ‘drift’ as it warms up. At 5 minutes it could be low then drift high and the swings may be in the order of .005Hz depending on the unit. The longer it stays on the more stable it becomes and oscillators like the LPRO-101 seem to settle faster than the FRK series but that doesn’t mean they will be any worse after they have been on a few hours. 

 The ‘TP’ output is a square wave for testing only and most users are interested in a clean sine wave. The 15Mhz output is amplified and passed through a low pass filter to remove any higher frequency harmonics and this output amp works great if you feed the much more useful 10Mhz through it instead of the less useful 15Mhz.

Rubidium oscillators are secondary, not primary standards and must be calibrated against a higher accuracy standard like a cesium beam or GPS standard. The adjustment range on a rubidium oscillator is generally some fraction of a hertz. The long term stability and accuracy of GPS is as close to absolute as most people can access so GPS is a good way to set the rubidium oscillator close to 10Mhz. I generally run the rubidium against a GPSDO and check for nanosecond drift over about an 8 hour period.   

For a quick check I use a pair of CNT-81 (Fluke/Philips 6681) counters locked to GPS and use the math function to display the frequency difference to 5 decimal places.

[4thDoctorWhoFan]

The 15Mhz output is amplified and passed through a low pass filter to remove any higher frequency harmonics and this output amp works great if you feed the much more useful 10Mhz through it instead of the less useful 15Mhz.

Has someone documented how to do this modification?

Rubidium oscillators are secondary, not primary standards and must be calibrated against a higher accuracy standard like a cesium beam or GPS standard.

I realize a RB is a secondary standard but I did not think a GPSDO was a higher standard.  I was under the impression that a GPSDO was one step down from a RB.

[ArthurDent]

Here is about a 15 hour plot of a rubidium oscillator against GPS. The white line shows that at any time the 10Mhz is well within 500ppt (parts per trillion) and the purple line shows cumulative drift over time. The line slope is constant indicating that the oscillator is very stable. I made an adjustment near the end but overcompensated. Over 12 hours the output only drifted about 40 ns, 1 hour=3.6e+12 ns.   

[4thDoctorWhoFan]

Here is about a 15 hour plot of a rubidium oscillator against GPS. The white line shows that at any time the 10Mhz is well within 500ppt (parts per trillion) and the purple line shows cumulative drift over time. The line slope is constant indicating that the oscillator is very stable. I made an adjustment near the end but overcompensated. Over 12 hours the output only drifted about 40 ns, 1 hour=3.6e+12 ns.

Awesome, thanks for that graph.
So any documentation on how to internally switch the 10Mhz to the 15Mhz amp?

[cncjerry]

Well my next question is how do I know just how accurate the 10Mhz output of the REF0 is? I have a PM6666 counter and I am looking to plug this 10Mhz into the extern ref input of the counter. If I do that I would then like to be able to measure other crystals. It seems if I measure for 10 seconds I can get a resolution on the counter of 10ppb which is just amazing!

What I would also like to do is measure stabiliy of some oxco. I think this is a whole different ball game but what equipment do I need to measure stabiliy of an oxco?

Look through the time-nuts archive.  Join if you are in the mood to spend money!

Stability means different things to different people.  If your REf0 is a recent purchase then if probably doesn't have an Rb unit but a decent DOCXO.  I think they were made by Milren.  Some are better than the Rbs, some aren't.  I have a pair of Lucent REf0/REF1 units running independently.  I also have 6 or 7 Rb units and a Cs beam.  Any or all can be used as a reference though some are better than others depending on the time period in question.  When you measure stability you use a reference.  The different units have different characteristics.  GPSDO for instance is good long term but within the correction cycle they are so-so, depending on the DOXCO you have.  Some Rb units have decent short term stability and some don't.  So far the only unit of mine that is really a decent reference is the Cs beam.  Lots of people say the square wave coming out of the REF0 units is "dirty".  Granted it doesn't look that great because it has the 5Mhz in it but you can make it look nice with a $10 BPF from eBay.  But then again a square wave transitions faster than a sine through the trigger level so there is debate about that as well. Anyway, look up Allan deviation and papers by Bill Riley on how to build a Dual Mixer Time Difference.  Or maybe a Tight PLL or Loose PLL unit if you want to measure oscillators. There is also a decent NIST paper on the subject.  This will get you started.

[trevwhite]

Thanks for all the replies.

The oscillator unit is a DOCXO by Milliren. I have left the REF0 unit on for about 12 hours. I also have my PM 6666 with ext ref of an OXCO - OH200-51003CF which has been on for 12 hours as well measuring the output of the REF0.

I am getting 9.9999996Mhz on the counter. This would indicate that they are within 40ppb of each other. I do not know how accurate over 12 hours the REF0 unit will become. Is there any information on how accurate the REF0 unit is after taking some time to tune in on the PPS signal and calibrate its own DOCXO?

[ArthurDent]

trevwhite, you state: “I am getting 9.9999996Mhz on the counter.”  What I showed on my counter using the math function was
  9,999,999.6         Mhz PM6666
10,000,000.00010  Mhz CNT-81

and the GPSDOs I’m using and my counter give me confidence in my readings. To get better resolution than your counter can display try triggering your scope on the REF 0 and set the timebase to around 10 or 2ns/div. Connect the 10Mhz output from your counter to the vertical channel and watch the waveform drift left or right.  There isn’t an actual output on your counter but a cable from the REF in to your scope may have enough leakage to pick up the signal if the scope is set to some low MV range. The drift will be superimposed on a waveform that is mostly noise but will allow you to see the drift. The .4Hz low your counter is displaying should show a fairly fast drift to the right of the screen. If your counter has a reasonable timebase you can first adjust your 9,999,999.6 reading to as close to 10Mhz as possible then use the scope method to get it closer.         

If you have connected the REF 0 the way it was in the article you referenced then the GPSDO you’ve created should be the more accurate of the two. If you use the Lady Heather software and connect a serial cable to the J8, DIAGNOSTIC jack on the front you can use RS-232 to create a graph similar to the one I created that will give you a lot of information on stability and accuracy of the Lucent unit. If you use the following connections you can use RS-232 instead of RS-422 and it seems to work o.k..  It’s also a good idea to leave the output level switch in the 17 position.
  PC            RFTG
DE-9S        DE-9P
5 <----GND--->7
3 TXD -------->8
2 RXD <------- 9

[SoundTech-LG]

 So far the only unit of mine that is really a decent reference is the Cs beam.  Lots of people say the square wave coming out of the REF0 units is "dirty".  Granted it doesn't look that great because it has the 5Mhz in it but you can make it look nice with a $10 BPF from eBay.  But then again a square wave transitions faster than a sine through the trigger level so there is debate about that as well. Anyway, look up Allan deviation and papers by Bill Riley on how to build a Dual Mixer Time Difference.  Or maybe a Tight PLL or Loose PLL unit if you want to measure oscillators. There is also a decent NIST paper on the subject.  This will get you started.
[/quote]

So, just acquired a Symmetricom Cs4000. Have not plugged it in yet. The seller said the Alarm Lamp was lit, and that was all he did. Well, of course the Alarm Lamp does light for the 1st half hour, or more, before it initializes. Especially after a long storage (assumption). I'm hoping it goes out quickly, and there is no problems here, otherwise it's a boat anchor. Know much about these???

[trevwhite]

I thought the pps signal would have jitter and would drift itself depending on how good the GPS module is?

[ArthurDent]

Explanation.

https://tf.nist.gov/general/pdf/2297.pdf

[trevwhite]

wow, thanks for the info.

I am going to try and get the REF0 wired up to the PC for some measurements.

[rubidium]

@SoundTech-LG: Any luck with your CS-4000? I just acquired a surplus unit myself and it communicates properly with the Monitor-3 software via RS323, but the alarm light hasn't gone out and the software continues indicating "Warming up" after 2 hours. Just wondering how you made out and if there are any insights you can offer from your experience. Or ... perhaps ... we each own a 45lb boat anchor.
Thanks,
Jim