Author Topic: Economical option for precision frequency reference?  (Read 117779 times)

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Online Gandalf_Sr

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Re: Economical option for precision frequency reference?
« Reply #325 on: November 27, 2015, 12:38:19 pm »
I may get a chance to test out my NTBW50AA today.  I bought it with the (perhaps slightly naive) idea that I could use the 10 MHz output as an external clock input to stuff like my N1996A and E4433B to get super accuracy.  Some research has shown that, unless the signal from the NTBW50AA plus distribution amp is better (lower phase noise and less jitter) then this is not a good idea so, until I do more research on that topic, I will use the 10 MHz output to check the calibration of my gear.
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Online Gandalf_Sr

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Re: Economical option for precision frequency reference?
« Reply #326 on: November 27, 2015, 05:00:24 pm »
Getting a bit frustrated, I'm trying to make Lady Heather talk to my NTBW50AA.  I bought a USB-RS232 cable and it installs on my Windows 10 system as COM4.  I'm pretty sure the cable connections are good but all that happens when I start LH is it says 'NO COM1 SERIAL PORT DATA SEEN' - I'm now trying Windows 8 compatibility mode and am running LH as Admin.

I added a heather.cfg file with nothing but '/4' in it but I still get the message about COM1 when LH starts up, I also tried typing in '/4' at the command interface.  I messed with various setting for the port - current settings are 9600, 8 bit, no parity, 1 stop bit

Any suggestions anyone?

[EDIT1] It seems it's a Lady Heather problem.  I have found the serial port setting and it's 19,200,7,Odd,1, and I think XOn/XOff, with these settings I can connect to Port 4 and then when I type '1' it responds with "E-113>
« Last Edit: November 27, 2015, 06:11:59 pm by Gandalf_Sr »
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Offline TheSteve

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Re: Economical option for precision frequency reference?
« Reply #327 on: November 27, 2015, 07:25:12 pm »
Unless its actually in use you can do the easy solution and just change the usb serial port to com1 - then the default LH settings will work fine.
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Online Gandalf_Sr

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Re: Economical option for precision frequency reference?
« Reply #328 on: November 28, 2015, 06:30:12 pm »
Unless its actually in use you can do the easy solution and just change the usb serial port to com1 - then the default LH settings will work fine.
Well duh!  That worked!  Thanks Steve :D
I believe the issue with Windows 10 is that they've changed the way 'My Documents' works and have some weird protection for where programs are allowed to access files from.  Steve's suggestion allowed LH to just use the defaults.
« Last Edit: November 28, 2015, 06:39:33 pm by Gandalf_Sr »
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Offline TheSteve

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Re: Economical option for precision frequency reference?
« Reply #329 on: November 28, 2015, 09:34:35 pm »
Unless its actually in use you can do the easy solution and just change the usb serial port to com1 - then the default LH settings will work fine.
Well duh!  That worked!  Thanks Steve :D
I believe the issue with Windows 10 is that they've changed the way 'My Documents' works and have some weird protection for where programs are allowed to access files from.  Steve's suggestion allowed LH to just use the defaults.

Excellent - lady Heather is a rather old school program, I run it on an old netbook running XP.
Btw your N1996A claims it can use PP2S for an external reference but it actually works with PPS only.
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Online Gandalf_Sr

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Re: Economical option for precision frequency reference?
« Reply #330 on: December 01, 2015, 12:19:08 am »
Did a test run with the antenna outside on a pole on my lawn just to make sure it was all working - it was, I'll post a picture tomorrow.  Now to do the proper installation but I need to do the modifications that Steve suggested to get 1 PPS out of the front panel.
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Offline Lightages

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Re: Economical option for precision frequency reference?
« Reply #331 on: December 01, 2015, 01:48:00 am »
I have been running my BG7TBL / 2014-12-09 for quite a while now and it is working fine. I have been trying to get it working as a source for an NTP server using the instructions at: http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html

I cannot get the receiver t change its settings to match the requirements to work at 4800 baud and use only $GPRMC sentences. I am using the u-center software but none of the settings I send take hold. With the default settings the NTP server software does not use the GPS as the clock.

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Online Gandalf_Sr

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Re: Economical option for precision frequency reference?
« Reply #332 on: December 01, 2015, 05:48:24 pm »
OK, here's some pictures for y'all.  Does everything look OK from the data?

[Edit] OK, let me ask the question in a different way. Can anyone help me to interpret the data I'm seeing?  Given my interest in knowing that the Nortel box is giving me accurate timings, what do these indications tell me...

PPS^ -0.293456 ns
Osc^ 11.567843 ppt

Thanks in advance.
« Last Edit: December 02, 2015, 12:26:33 pm by Gandalf_Sr »
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Offline TheSteve

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Re: Economical option for precision frequency reference?
« Reply #333 on: December 07, 2015, 03:58:22 am »
Did another small mod to my Nortel NTBW50AA that I've been meaning to do for a long time now. Instead of messing with the SMB connectors on the front I drilled a few holes on the back of the chassis and mounted BNC connectors for the GPS antenna in, 1 PPS and 10 MHz outputs. If you mount them on the back of the chassis you only need to drill through one layer of steel, use a step bit and the drilling is very easy. A few runs of coax cable run neatly under the PCB soldered to the SMB jacks or any other proper point on the PCB and you're done.
You can also see my power cable that runs through a rubber grommet installed in an existing chassis hole. The cable goes to a 2.1mm connector so I can use a 24 VDC wall adapter to power the unit.
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Offline Bryan

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Re: Economical option for precision frequency reference?
« Reply #334 on: December 07, 2015, 11:49:52 am »
Getting a bit frustrated, I'm trying to make Lady Heather talk to my NTBW50AA.  I bought a USB-RS232 cable and it installs on my Windows 10 system as COM4.  I'm pretty sure the cable connections are good but all that happens when I start LH is it says 'NO COM1 SERIAL PORT DATA SEEN' - I'm now trying Windows 8 compatibility mode and am running LH as Admin.

I added a heather.cfg file with nothing but '/4' in it but I still get the message about COM1 when LH starts up, I also tried typing in '/4' at the command interface.  I messed with various setting for the port - current settings are 9600, 8 bit, no parity, 1 stop bit

Any suggestions anyone?

[EDIT1] It seems it's a Lady Heather problem.  I have found the serial port setting and it's 19,200,7,Odd,1, and I think XOn/XOff, with these settings I can connect to Port 4 and then when I type '1' it responds with "E-113>

Have my Nortel working fine with LH on Windows 10 on Com 1. You may want to try a download of tboltmon.exe and try a hard or cold reset. I assume your ports in device manager are set properly. Mine are 9600,8,none,1. no flow control.
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Online Gandalf_Sr

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Re: Economical option for precision frequency reference?
« Reply #335 on: December 28, 2015, 07:40:43 pm »
Getting a bit frustrated, I'm trying to make Lady Heather talk to my NTBW50AA.  I bought a USB-RS232 cable and it installs on my Windows 10 system as COM4.  I'm pretty sure the cable connections are good but all that happens when I start LH is it says 'NO COM1 SERIAL PORT DATA SEEN' - I'm now trying Windows 8 compatibility mode and am running LH as Admin.

I added a heather.cfg file with nothing but '/4' in it but I still get the message about COM1 when LH starts up, I also tried typing in '/4' at the command interface.  I messed with various setting for the port - current settings are 9600, 8 bit, no parity, 1 stop bit

Any suggestions anyone?

[EDIT1] It seems it's a Lady Heather problem.  I have found the serial port setting and it's 19,200,7,Odd,1, and I think XOn/XOff, with these settings I can connect to Port 4 and then when I type '1' it responds with "E-113>

Have my Nortel working fine with LH on Windows 10 on Com 1. You may want to try a download of tboltmon.exe and try a hard or cold reset. I assume your ports in device manager are set properly. Mine are 9600,8,none,1. no flow control.
Bryan, thanks for the input.  I did get Lady Heather working on Windows 10, the issue is that the OS protects itself by not allowing unknown software to read from the actual location it's installed in so the instructions to place the Heather.cfg file in the same folder as the .exe file are wrong but, in fact, the '?' function tells you (all the way at the end), that the heather.cfg file needs to be in c:\user\<yourname>\OneDrive\Documents and when the file is placed there, it works. There are some issues if you try to change screen resolution but that's OK.
« Last Edit: December 28, 2015, 09:29:58 pm by Gandalf_Sr »
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Offline N8AUM

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Re: Economical option for precision frequency reference?
« Reply #336 on: December 28, 2015, 09:50:00 pm »
I also had problems with Lady Heather. Tried different com port settings with her AND windblows 7. Ended up installing an old serial I/O board in one of the slots so that it would be com1.

 
 

Offline TheSteve

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Re: Economical option for precision frequency reference?
« Reply #337 on: December 31, 2015, 12:49:43 am »
Due to a GPSDO sickness and too much time spent trolling ebay I bought another GPSDO. This is an HP 58540A - likely built to compete with the Trimble Thunderbolt.
It has an SCPI interface, it doesn't provide a ton of functions and is pretty basic overall. It uses a single 24 VDC supply and has a switching supply under the timing board which provides the needed voltages. I need to run it for a month or two before really seeing how it compares with my Trimble units.

« Last Edit: April 17, 2016, 07:59:59 am by TheSteve »
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Offline Vgkid

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Re: Economical option for precision frequency reference?
« Reply #338 on: December 31, 2015, 12:55:24 am »
I wonder what the trimpot does?
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Offline TheSteve

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Re: Economical option for precision frequency reference?
« Reply #339 on: December 31, 2015, 01:05:45 am »
I wonder what the trimpot does?
Probably something boring like setting the 10 MHz output level.
« Last Edit: December 31, 2015, 01:07:37 am by TheSteve »
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Offline Vgkid

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Re: Economical option for precision frequency reference?
« Reply #340 on: December 31, 2015, 01:57:26 am »
That makes sense, I believe that they do that in the lucent boxes.
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Offline N8AUM

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Re: Economical option for precision frequency reference?
« Reply #341 on: December 31, 2015, 02:02:25 am »
cool serial # the osc. !
 

Offline TheSteve

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Re: Economical option for precision frequency reference?
« Reply #342 on: December 31, 2015, 02:19:09 am »
cool serial # the osc. !

Yeah, not sure how many of these they made. Google doesn't give too much info but the others I have seen use a different OCXO. The PCB layout fits several different OCXO models. It would be nice to upgrade it to something newer with lower phase noise but the odds of finding one that is drop in compatible with the hardware and firmware seems pretty slim.
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Offline dannyf

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Re: Economical option for precision frequency reference?
« Reply #343 on: December 31, 2015, 03:10:40 pm »
Quote
But what I'd really like is if someone can give me some practical suggestions on what is the most practical way to set up a good frequency reference - what is needed, and what's the best place to source one.

A few approaches, depending on what you want to do:

1) (VC)TCXO: usually good for 2.5ppm max - and typically < 0.5ppm at room temperature. Cheap and lots of frequency options;
2) GPS: slightly more expensive, but many are programmable so you can generate whatever frequencies you so desire.

I used a hybrid approach: I built a platform that adjusts a VCTCXO's output to a GPS. Once caliberated, that VCTCXO can operate without the GPS. Done on a PIC16F684 but should be easily adopted onto other platforms, as it is essentially a phase comparator.
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Offline Bryan

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Re: Economical option for precision frequency reference?
« Reply #344 on: January 01, 2016, 09:40:53 pm »

Have my Nortel working fine with LH on Windows 10 on Com 1. You may want to try a download of tboltmon.exe and try a hard or cold reset. I assume your ports in device manager are set properly. Mine are 9600,8,none,1. no flow control.
Bryan, thanks for the input.  I did get Lady Heather working on Windows 10, the issue is that the OS protects itself by not allowing unknown software to read from the actual location it's installed in so the instructions to place the Heather.cfg file in the same folder as the .exe file are wrong but, in fact, the '?' function tells you (all the way at the end), that the heather.cfg file needs to be in c:\user\<yourname>\OneDrive\Documents and when the file is placed there, it works. There are some issues if you try to change screen resolution but that's OK.

Yes, I noticed the same thing when trying to adjust the screen resolution , it will crash. Too bad it has not been updated since 2013, I think it is a great program. Would be great if it could be upgraded to incorporate some of the other GPSDO boxes out there. 

Another tip if I could share is to do a Autotune of the oscillator after it has been running for a number of months "&" then "A"
« Last Edit: January 02, 2016, 10:17:22 pm by Bryan »
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Offline _Andrew_

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Re: Economical option for precision frequency reference?
« Reply #345 on: January 02, 2016, 03:25:37 am »
Stumbled across these OCXO & GPS TCXO reference oscillators from Total Frequency Control

http://www.tfc.co.uk/products.php?CategoryID=3&gclid=CKmYp_-TisoCFRUTGwodmu4Bbw

http://www.tfc.co.uk/products.php?CategoryID=6&SubID=3



 
 

Offline TheSteve

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Re: Economical option for precision frequency reference?
« Reply #346 on: January 04, 2016, 05:15:21 am »
Thought I would compare the 1 PPS outputs from the three GPSDO's I have here.

The blue trace is the Nortel NTGS50AA which is the trigger channel
The yellow trace is the cheapie Trimble 57964-15 with 63090 OCXO
The purple trace is the HP 58540A

The scope has been running on infinite persistence for a few hours.
You can see the jitter on the HP is probably double what it is on either of the others(I have triggered on the Trimble with similar results).
I have changed the antenna delay to get them to be reasonably close on the scope so it is easier to see. By default the Nortel leads the Trimble by roughly 500ns which leads the HP by 100ns. So even with 3 GPSDO's I have no idea when the pulse really occurs :)
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Offline edpalmer42

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Re: Economical option for precision frequency reference?
« Reply #347 on: January 04, 2016, 06:54:33 am »
Now do the same test with 3 of your Rb oscillators.  You'll be shocked by the difference!  :o  Over a period of a few hours, the Rb oscillators are more stable than the GPSDOs.  It's only over longer time frames that the long-term frequency stability of the GPSDO starts to show its advantage over the Rb standard.

Of course, we have to remember that these GPSDOs are not optomized to give the lowest possible jitter.  You could make the time constants longer, but there are tradeoffs there too.  The same applies to the Rb units.  Low jitter just wasn't one of the design requirements.

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Offline TheSteve

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Re: Economical option for precision frequency reference?
« Reply #348 on: January 04, 2016, 07:22:41 am »
Now do the same test with 3 of your Rb oscillators.  You'll be shocked by the difference!  :o  Over a period of a few hours, the Rb oscillators are more stable than the GPSDOs.  It's only over longer time frames that the long-term frequency stability of the GPSDO starts to show its advantage over the Rb standard.

Of course, we have to remember that these GPSDOs are not optomized to give the lowest possible jitter.  You could make the time constants longer, but there are tradeoffs there too.  The same applies to the Rb units.  Low jitter just wasn't one of the design requirements.

Ed

The Rb's I have here don't have a 1 PPS output. I can watch the 10 MHz out but they will all wander a little as none are at exactly 10 MHz and it isn't possible to set them perfectly I don't think. The rate of wander is likely constant though which is what counts.
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Offline Bryan

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Re: Economical option for precision frequency reference?
« Reply #349 on: January 04, 2016, 09:55:07 am »
Now do the same test with 3 of your Rb oscillators.  You'll be shocked by the difference!  :o  Over a period of a few hours, the Rb oscillators are more stable than the GPSDOs.  It's only over longer time frames that the long-term frequency stability of the GPSDO starts to show its advantage over the Rb standard.

Of course, we have to remember that these GPSDOs are not optomized to give the lowest possible jitter.  You could make the time constants longer, but there are tradeoffs there too.  The same applies to the Rb units.  Low jitter just wasn't one of the design requirements.

Ed


Taking this into consideration what is the best way to "adjust" a RB to a GPSDO or is it really feasible to do so considering the GPSDO is better long term, but suffers from short term stability.
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