Author Topic: bg7tbl gpsdo master reference  (Read 145814 times)

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Offline SeanB

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Re: bg7tbl gpsdo master reference
« Reply #125 on: September 14, 2015, 04:30:45 am »
If the window sees sky ( no matter how little, the view you have will give you at least 2 signals and the GPS will eventually lock with that) just a plain GPS antenna on the sill will work. I have a small GPS that works fine just on the sill in a similar situation, and it will lock from cold in under 20 minutes. That one has a plain ceramic patch antenna, and was originally a bluetooth unit, though it does do serial comms on the charge USB mini cable ( naughty, should be USB but is serial TTL) so I hacked up a USB cable to put an old Nokia serial adaptor ( old nokia clone cable for older phones without USB) in line.
« Last Edit: September 14, 2015, 04:33:19 am by SeanB »
 

Offline edpalmer42

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Re: bg7tbl gpsdo master reference
« Reply #126 on: September 14, 2015, 04:45:57 am »
One thing to consider is that a new, super-sensitive GPS receiver is quite capable of picking up signals that an older, slightly deaf unit would ignore.  Sounds good, but you might find that the older unit performs better because it's ignoring the reflected multipath signals that you really don't want to pick up.

As I understand it, when a GPS signal gets reflected, it changes from Right Hand Circularly Polarized to Left Hand Circularly Polarized.  The receiver tends to reject the left hand signal, but the rejection isn't perfect.  Timing antennas usually have better filtering, both for off-frequency and wrong-polarization signals so they can perform better in less than perfect situations than a regular antenna.

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Offline TSL

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Re: bg7tbl gpsdo master reference
« Reply #127 on: September 14, 2015, 06:59:07 am »
@neopticus If you are serious about wanting a reference to set others by then you need a GPSDO that's on all the time. You mention using a rubidium to run by and calibrate that by GPSDO every month or so. If that's the case then you need a very good GPSDO and it would have to be on all the time to reach a resolution that would exceed that of the rubidium.

Proper timing GPSDO's such as Trimble Thunderbolts, allow you to tune their behavior to your location. i.e. you can set an elevation mask to minimize multi-path interference, change the loop time constant and damping factors. You also need a clear view of the sky for as many satellites as possible to get the best possible accuracy.

A good GPSDO will also profile their own OCXO's so that when sats are obscured and they go into holdover, the oscillator is steered in the best possible way to maintain the highest possible accuracy until enough sats are visible again to steer things properly.

And if precise time is your thing it a good GPSDO allows you to insert a propagation delay for the length of cable between the unit and the antenna to get that last 60 odd ns out of the way.

Also it can take a month for a GPSDO to attain 1E-12 or better accuracy and keep it.

You have to ask yourself... "What level of accuracy for 10MHz or 1PPS do I want ?"

There are many proper GPSDO's for reference & timing available on eBay for such purposes without spending too much money.

e.g.

http://www.ebay.com/itm/HP-SYMMETRICOM-Z3805A-GPS-Disciplined-Oscillator-GPS-Frequency-Time-Receiver-/171293077196

http://www.ebay.com/itm/HP-Z3815A-GPS-Frequency-Time-Receiver-GPS-disciplined-oscillator-10-Mhz-1PPS/171293069062

http://www.ebay.com/itm/FEI-PicoSync-GPS-Time-Frequency-Engine-GPS-Disciplined-Oscillator-10MHZ-PP2S/181389532308

http://www.ebay.com/itm/HP-Z3816A-GPS-Frequency-Time-Receiver-10-Mhz-1PPS-/271906200825

just to name a few.


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Offline Electro Fan

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Re: bg7tbl gpsdo master reference
« Reply #128 on: September 14, 2015, 07:19:30 am »
Sorry if this one has already been discussed, but any feedback on this?  Just a monitor - any practical benefit, or just as easy/better to use a computer?

http://www.ebay.com/itm/Trimble-ThunderBoltTiming-GPS-Receiver-GPSDO-10MHz-GPS-Disciplined-Clock-Monitor-/181792660863?hash=item2a53afdd7f
« Last Edit: September 14, 2015, 07:21:22 am by Electro Fan »
 

Offline TSL

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Re: bg7tbl gpsdo master reference
« Reply #129 on: September 14, 2015, 07:33:38 am »
Sorry if this one has already been discussed, but any feedback on this?  Just a monitor - any practical benefit, or just as easy/better to use a computer?

http://www.ebay.com/itm/Trimble-ThunderBoltTiming-GPS-Receiver-GPSDO-10MHz-GPS-Disciplined-Clock-Monitor-/181792660863?hash=item2a53afdd7f

I have something similar. There's been a few different types getting about.

These are useful if you have built your TB into a nice box and you just want to keep an eye on it. Most GPSDO's have no display since once set and tuned you only need a warning LED or two to let you know if something goes awry.

At least these displays give you an idea if something is a bit off and needs ore attention.
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Offline neopticus

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Re: bg7tbl gpsdo master reference
« Reply #130 on: September 15, 2015, 04:29:42 am »
@neopticus If you are serious about wanting a reference to set others by then you need a GPSDO that's on all the time. You mention using a rubidium to run by and calibrate that by GPSDO every month or so. If that's the case then you need a very good GPSDO and it would have to be on all the time to reach a resolution that would exceed that of the rubidium.

Proper timing GPSDO's such as Trimble Thunderbolts, allow you to tune their behavior to your location. i.e. you can set an elevation mask to minimize multi-path interference, change the loop time constant and damping factors. You also need a clear view of the sky for as many satellites as possible to get the best possible accuracy.

A good GPSDO will also profile their own OCXO's so that when sats are obscured and they go into holdover, the oscillator is steered in the best possible way to maintain the highest possible accuracy until enough sats are visible again to steer things properly.

And if precise time is your thing it a good GPSDO allows you to insert a propagation delay for the length of cable between the unit and the antenna to get that last 60 odd ns out of the way.

Also it can take a month for a GPSDO to attain 1E-12 or better accuracy and keep it.

You have to ask yourself... "What level of accuracy for 10MHz or 1PPS do I want ?"

There are many proper GPSDO's for reference & timing available on eBay for such purposes without spending too much money.

e.g.

http://www.ebay.com/itm/HP-SYMMETRICOM-Z3805A-GPS-Disciplined-Oscillator-GPS-Frequency-Time-Receiver-/171293077196

http://www.ebay.com/itm/HP-Z3815A-GPS-Frequency-Time-Receiver-GPS-disciplined-oscillator-10-Mhz-1PPS/171293069062

http://www.ebay.com/itm/FEI-PicoSync-GPS-Time-Frequency-Engine-GPS-Disciplined-Oscillator-10MHZ-PP2S/181389532308

http://www.ebay.com/itm/HP-Z3816A-GPS-Frequency-Time-Receiver-10-Mhz-1PPS-/271906200825

just to name a few.

TSL, thanks for your advice. I was aware that the professional systems for timekeeping are more accurate, but since they are too insensitive (to be be used in my apartment), they were ruled out pretty fast. As such, the list of eBay items you gave is not is not useful in my case. But I appreciate the effort, and I think many budget restricted (but not open sky restricted :) ) members here will appreciate it too!

I should have been more precise (no pun intended) in my description of the use case: I mentioned checking the rubidium (as in "is it on the same ballpark as GPSDO?" or "not-drifted or completely failed") but not necessarily calibrating it to its highest possible accuracy.

As I've understood, Rb standards are accurate in 10e-11 level, and to calibrate them an accuracy of at least 10e-12 is needed, which would then require 24h running, high end GPSDO with at least few weeks uptime, as you mentioned.

Now, to my use case: Here are some examples of the OCXOs I have in my possession:
HP 53132A option 010: Temp stability: <2 x 10e-9. Turn-on stability 30 min:  <5 x 10-9. Aging: <1.5 x 10e-8/month
CMU200 option B12: Temp stability < 5 × 10e–9. Turn-on stability 2h: ±5 × 10e–9. Aging ±3.5 × 10e–8/year.
HP 8657A option 001: Temp stability: <7 x 10e-9. Aging < 3 x 10e-8/month.

Calibrating these would need accuracy of just 10e-10, so anything better than this is basically just money thrown away, right?

I read the review of BG7TBL 2014-12-09 by Tim Tuck (link on the first page) and there he states: "After a few hours the frequency settles further to within a Milli Hz or so of 10MHz."
This would be accuracy of level 10e-10 to e-11 and well enough for my needs, or is there something I have failed to grasp here? 

 

Offline usagi

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Re: bg7tbl gpsdo master reference
« Reply #131 on: September 15, 2015, 05:04:31 pm »
even the 'flawed' bg7tbl is beyond most hobbyists requirements.

Offline TSL

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Re: bg7tbl gpsdo master reference
« Reply #132 on: September 15, 2015, 06:04:10 pm »

TSL, thanks for your advice. I was aware that the professional systems for timekeeping are more accurate, but since they are too insensitive (to be be used in my apartment), they were ruled out pretty fast. As such, the list of eBay items you gave is not is not useful in my case. But I appreciate the effort, and I think many budget restricted (but not open sky restricted :) ) members here will appreciate it too!

Fair enough - or... you could add a big arsed powered antenna to them, like this guy...

http://www.ebay.com/itm/Symmetricom-58532A-GPS-L1-Reference-Antenna-NEW-IN-BOX-QTY-in-Stock-/271918319682

This has a whopping 38dBi of gain and inbuilt filters to help overcome deafness and long cable runs. I have one of those on my roof :)


I should have been more precise (no pun intended) in my description of the use case: I mentioned checking the rubidium (as in "is it on the same ballpark as GPSDO?" or "not-drifted or completely failed") but not necessarily calibrating it to its highest possible accuracy.

As I've understood, Rb standards are accurate in 10e-11 level, and to calibrate them an accuracy of at least 10e-12 is needed, which would then require 24h running, high end GPSDO with at least few weeks uptime, as you mentioned.

Now, to my use case: Here are some examples of the OCXOs I have in my possession:
HP 53132A option 010: Temp stability: <2 x 10e-9. Turn-on stability 30 min:  <5 x 10-9. Aging: <1.5 x 10e-8/month
CMU200 option B12: Temp stability < 5 × 10e–9. Turn-on stability 2h: ±5 × 10e–9. Aging ±3.5 × 10e–8/year.
HP 8657A option 001: Temp stability: <7 x 10e-9. Aging < 3 x 10e-8/month.

Calibrating these would need accuracy of just 10e-10, so anything better than this is basically just money thrown away, right?

I wouldn't consider it "throwing money away" but if you can get the resolution you want for the right $, if that spec is better than you need - that's a good thing.


I read the review of BG7TBL 2014-12-09 by Tim Tuck (link on the first page) and there he states: "After a few hours the frequency settles further to within a Milli Hz or so of 10MHz."

I did say that didn't I :)

I should do some Allen Deviation tests on this unit to see if my measurements are close or same to KE5FX's

This would be accuracy of level 10e-10 to e-11 and well enough for my needs, or is there something I have failed to grasp here?

Nope, you've grasped it :)


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Offline bingo600

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Re: bg7tbl gpsdo master reference
« Reply #133 on: September 17, 2015, 12:47:31 am »


Fair enough - or... you could add a big arsed powered antenna to them, like this guy...

http://www.ebay.com/itm/Symmetricom-58532A-GPS-L1-Reference-Antenna-NEW-IN-BOX-QTY-in-Stock-/271918319682

This has a whopping 38dBi of gain and inbuilt filters to help overcome deafness and long cable runs. I have one of those on my roof :)

Nope, you've grasped it :)

I just had to "downgrade" my 40dB Lucent "IceCone" to a 26dB model.
The reason was "too strong signal", on two of my gpsdo's.

I'm using 25m quad shielded cable to a 4-chan active GPS antenna splitter (w. 10dB gain)
And that combi, delivered too much gain.

So i'd watch out for getting a 40dB with short cable runs.

/Bingo
 

Offline usagi

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Re: bg7tbl gpsdo master reference
« Reply #134 on: September 17, 2015, 05:11:06 am »
couldn't you just add an inline attenuator if it was too hot for a specific device?

Offline TSL

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Re: bg7tbl gpsdo master reference
« Reply #135 on: September 17, 2015, 09:29:14 am »
couldn't you just add an inline attenuator if it was too hot for a specific device?

Yep he could have done that - there are plenty of 2GHz rated units around, problem is most of them cost more than a new antenna! even if you find the cheap ones, 2 of them could end costing more than a new antenna.
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Offline bingo600

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Re: bg7tbl gpsdo master reference
« Reply #136 on: September 18, 2015, 06:35:38 am »
couldn't you just add an inline attenuator if it was too hot for a specific device?

Yep he could have done that - there are plenty of 2GHz rated units around, problem is most of them cost more than a new antenna! even if you find the cheap ones, 2 of them could end costing more than a new antenna.

And i'd need one with DC pass through, as the antenna still want's it's 5v.
MiniCircout have some , but i almost same price as the new 26dB

Another is the antenna-psu load sense on the GPs'es , you'd still want to load it with 50ohm , or you might end up in an antenna error from the GPS.

/Bingo
« Last Edit: September 18, 2015, 06:37:54 am by bingo600 »
 

Offline janekivi

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Re: bg7tbl gpsdo master reference
« Reply #137 on: September 28, 2015, 05:04:13 am »
For BG7TBL 2015-07-17 there is monitor program.
In the manual is more pictures and software You can get if if You bought this.

http://www.ebay.com/itm/181810679481?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
 

Offline Electro Fan

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Re: bg7tbl gpsdo master reference
« Reply #138 on: October 08, 2015, 04:03:38 pm »
I haven't keep up with this thread and the others on GPSDOs but I saw this:

http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-Antenna-power-/131564496688?hash=item1ea1dae730

It looks similar to the one in the post above by janekivi (maybe just a different seller).

Any chance these parts are really from Trimble or they just say Trimble?

Thanks
« Last Edit: October 08, 2015, 04:06:05 pm by Electro Fan »
 

Online TheSteve

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Re: bg7tbl gpsdo master reference
« Reply #139 on: October 08, 2015, 04:17:07 pm »
The board inside really is made by Trimble. I have just the board itself and have been testing it out - only received it yesterday so it hasn't settled down yet. motocoder has a Trimble unit and has made some comments about it in this thread - http://www.eevblog.com/forum/testgear/economical-option-for-precision-frequency-reference/
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Offline usagi

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Re: bg7tbl gpsdo master reference
« Reply #140 on: October 08, 2015, 05:06:35 pm »
the trimble isn't a bad choice, the ublox just has far superior sensitivity.

any of the bg7tbl units are superior to the lucent imo.

Offline SHF

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Re: bg7tbl gpsdo master reference
« Reply #141 on: December 04, 2015, 07:10:40 am »
Hello !
Could someone read the configuration of the U-blox NEO-6 GPS-Receiver ?
The can be easily read with the program u-Center!
I do not know if my still fits ..!?
Many thanks ! Dieter


« Last Edit: December 04, 2015, 07:41:57 am by SHF »
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Offline Lightages

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Re: bg7tbl gpsdo master reference
« Reply #142 on: December 04, 2015, 11:57:36 am »
I have been trying to reconfigure mine too so I can use it for an NTP server, but the settings don't work. I am looking for help with u-blox software too.
 

Offline Vgkid

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Re: bg7tbl gpsdo master reference
« Reply #143 on: December 04, 2015, 01:30:48 pm »
The ublox software is really easy to use(at least over usb) but unless there is a a memory chip for the gps receiver, any modifications to what you want differently will be interesting. You will have to dive into the U-blox documents if you want to program the chip(without powering it down). In other words you will need to trick the PC.GPS to communicate w/each other w/o sending power to each other.
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Offline Lightages

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Re: bg7tbl gpsdo master reference
« Reply #144 on: December 04, 2015, 03:14:15 pm »
I am trying to change the baud rate and sentence types sent by the receiver, but nothing changes or sticks.
 

Offline edpalmer42

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Re: bg7tbl gpsdo master reference
« Reply #145 on: December 04, 2015, 03:33:47 pm »
I am trying to change the baud rate and sentence types sent by the receiver, but nothing changes or sticks.

I'm confused by all the different versions that BG7TBL has put out.  Are you sure that the u-blox chip is wired to the RS-232 port?  I remember that at least one version only had the transmit lead wired out so you could receive the output from the GPS chip, but you couldn't talk to it.

Ed
 

Offline usagi

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Re: bg7tbl gpsdo master reference
« Reply #146 on: December 04, 2015, 06:24:46 pm »
"2015-09-17"

custom board with surplus russian morion mv201 OCXO. gps is u-blox NEO-6M-0-001


Offline SHF

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Re: bg7tbl gpsdo master reference
« Reply #147 on: December 06, 2015, 06:04:04 am »
Does anyone know what  voltage the lithium battery is supposed to have? 3.6V?
I measure 1.9 volts !!
if you have the battery replaced then the settings GPS neo-6M away?
Greeting, Dieter
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Offline usagi

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Re: bg7tbl gpsdo master reference
« Reply #148 on: December 06, 2015, 08:05:59 am »
Does anyone know what  voltage the lithium battery is supposed to have? 3.6V?
I measure 1.9 volts !!
if you have the battery replaced then the settings GPS neo-6M away?
Greeting, Dieter

according to the datasheet, the battery is for supporting gps hotstart / warmstart. supported voltage is 1.4v - 3.6v

Offline SHF

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Re: bg7tbl gpsdo master reference
« Reply #149 on: December 07, 2015, 12:35:37 am »
 -->> according to the datasheet, the battery is for supporting gps hotstart / warmstart. supported voltage is 1.4v - 3.6v
 
Thank you for your reply !!!!
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