Author Topic: bg7tbl gpsdo master reference  (Read 259727 times)

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Offline Noy

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Re: bg7tbl gpsdo master reference
« Reply #875 on: February 28, 2021, 07:36:46 pm »
You really put a 80€ module into an 80€ GPSDO?
Wow and i thought about the 25€ Neo-M9N if it is worth..
Unfortunally i have to replace the Atmega8A with new Software. Neo-9 wants to talk fast er than 9600baud..
 

Offline Ringmodulator

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Re: bg7tbl gpsdo master reference
« Reply #876 on: March 01, 2021, 11:12:45 am »
You really put a 80€ module into an 80€ GPSDO?
Wow and i thought about the 25€ Neo-M9N if it is worth..
Unfortunally i have to replace the Atmega8A with new Software. Neo-9 wants to talk fast er than 9600baud..

Yes, really!

It  was a used module for like 16€. So that puts it somewhat in perspective.

 

Offline Noy

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Re: bg7tbl gpsdo master reference
« Reply #877 on: March 01, 2021, 11:31:48 am »
Are there more M8T for 16€ in your source?
Is it truly a genuine one? Found used ones in eBay but im concerned if they are still working / genuine. Would be easier than reprogramming the atmega8. Whats special about m8t vs m9n?
« Last Edit: March 01, 2021, 11:35:50 am by Noy »
 

Offline Noy

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Re: bg7tbl gpsdo master reference
« Reply #878 on: March 01, 2021, 06:56:43 pm »
Answer to myself... M8T has specified lower jitter..
EBay seller will auto accept for 15$..
Now i will get one and try..
I can save the "expensive" Neo-M9N for something which needs navigation..

Hopefully i will not kill the PCB this time first time was OK second time removing the module we will See..
 

Offline Ringmodulator

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Re: bg7tbl gpsdo master reference
« Reply #879 on: March 02, 2021, 03:19:15 pm »
Answer to myself... M8T has specified lower jitter..
EBay seller will auto accept for 15$..
Now i will get one and try..
I can save the "expensive" Neo-M9N for something which needs navigation..

Hopefully i will not kill the PCB this time first time was OK second time removing the module we will See..

I got mine probably from the same seller.

They just cut the pcb with the module on it.
I did heat the pcb from the backside with hot air until the module just fell off.

I think, these are genuine modules from decomissioned commercial gear, which probably would not be equipped with fake ones.

To remove the module on the gpsdo, I used a tweezer type soldering iron with tips was wide as the module.
You need quite some heat.
It finally worked, but it was not really elegant and a risk always remains.

 

Offline MegaVolt

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Re: bg7tbl gpsdo master reference
« Reply #880 on: March 04, 2021, 01:38:23 pm »
I would like to buy myself a similar standard. But there are so many offers that I am at a loss.
Some sellers offer a choice of any two standards. Does it mean that they have a more modern receiver?
Is it right to choose the BDS + GALILEO combination as more modern and accurate?
Will I be able to switch the used standards myself?
I see a proposal with HP / Agilent 10811 OCXO inside. But there is no screen and no choice of GPS standards.
I heard that they have a small static error. Perhaps there are models where this problem is solved?
What else is worth paying attention to?
 

Online nctnico

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Re: bg7tbl gpsdo master reference
« Reply #881 on: March 04, 2021, 02:35:19 pm »
AFAIK GPS has the most satellites in the sky and best coverage. Another thing to consider is that all these systems have a slightly different time source (based on country/region of origin) so they can (have to) drift a bit when compared to eachother. Perfect time doesn't exist; it is always an approximation.

The unit from BG7TBL is OK (but make sure you get at least a 2019 version). A couple of days ago I also ordered a unit based on a (surplus) Trimble GPSDO module to have a comparison.
« Last Edit: March 04, 2021, 02:37:11 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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Offline Noy

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Re: bg7tbl gpsdo master reference
« Reply #882 on: March 19, 2021, 02:11:30 pm »
So the M8T arraived..
Had some trouble changing everything back..removed the cut out pcb with my hotair and a (not so good) little bump an my silicon mat... Shield fell off and a tiny tiny little antenna part (i think the antenna supply switch) in the module.. But i think i repaired it with a lot of flux and hotair. The module gets a fix pretty fast...)
But it looks like the module is working.
Unfortunally the genuine atmega8 is not accepting the UART output from m8t..
The atmel shows still ALM because something he expected is missing. Is it really working with the genuine atmega @ Ringmodulator ??

I connected it to ucenter to clean the SPI flash maybe there is still some old configuration but it looks like i cannot  clean the configuration. It is also only using GPS and Glonass not Galileo vor Baidou and i can not enable them. Maybe i use the control Software wrong??

If i cannot get it to work with the old atmega i still have to rewrite the code..:-(

« Last Edit: March 19, 2021, 02:14:50 pm by Noy »
 

Offline burkm

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Re: bg7tbl gpsdo master reference
« Reply #883 on: June 02, 2021, 11:13:48 am »
My guess: Either you got an older version of the BG7TBL GPSDO, which has a different interface on the Atmega8 side or you got a chip clone. The problem could be an Ublox M8 clone from China, which is a common problem. Sometimes  even the label does not match the chip underneath in terms of version. or variante. A missing flash memory might be an indication of this too. Those Ublox chip clones / fakes seem to be all over the place in Asia, looking the same from the outside and often carry a fake Ublox label too. Even Ublox has already reacted to this and has a note about this on their Swiss website. The clones (Ublox fakes) seem to differ internally regarding the chip version, features and precision (sometimes or often) but are available a lot cheaper to a potential buyer, thus a whole industry seems to have been focused on this. They seem to be working "OK" just navigating, but lack some advertised features. It might help to buy the originals (new) either from the manufacturer directly or from a well known supplier (Digikey, Mouser etc.) or used ones taken from a well known seller and source like Huawei modules. Ublox u-center software might be used to identify those clones because it will report an error if something is missing.

You will find several YouTube videos about those clones when looking specifically for it...
« Last Edit: June 08, 2021, 05:49:30 am by burkm »
 

Offline cdev

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Re: bg7tbl gpsdo master reference
« Reply #884 on: June 02, 2021, 11:43:53 pm »
Many of them are supposed to have an internal TCXO but don't have it. So they are less accurate -substantially less accurate than they should be.
"What the large print giveth, the small print taketh away."
 

Offline burkm

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Re: bg7tbl gpsdo master reference
« Reply #885 on: June 13, 2021, 09:43:19 am »
When reading through all the posts here in this thread and looking through the accompanying pictures I got the impression, that many BG7TBL GPSDO units don't have a "real" U-blox GPS chip installed but one of the many Chinese copies ("fakes") floating around on the Chinese internet. U-Blox themselves warns about this too, because they seem to have experienced the same when buying their own chips from some of the better known online market places or dealers in China. Seems to become a general and common problem nowadays. They name Ebay or AliExpress as one of the sources for this and have provided some exemplary samples for this taken from complaining users posts. Some dealers / "manufacturers" sold items, which had removed the label altogether, some have a fake label and some show a "compatible" but different chip family (and manufacturer) when looking at the init messages. Some even show false version labels, hiding an older chip version pretending to be a newer one. Other clones lack the standard flash chip or have an "original" U-blox GPS chip but the rest is of lower quality as the real thing. They usually sell for a lot less when bought this way. BG7TBL probably doesn't seem to care as long as they are functional one way or the other and has not provided any GPS chip specific information.  :palm:  |O

The problem for the uninformed Buyer seems to be, that there are so many copied / fake ones nowadays, that it is hard to tell them apart most of the time, when just looking at them from the outside or by opening the unit's housing. It seems to me, that buying only from U-blox directly (expensive) or one of the "official" resellers / distributors or trusted sources, when "used",  will provide the needed security to get an "original" U-blox chip.

Are there any information available about replacing the "U-blox" GPS chip (old=>new), when one wants to be sure ?
« Last Edit: June 13, 2021, 10:03:16 am by burkm »
 

Online AndrewBCN

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Re: bg7tbl gpsdo master reference
« Reply #886 on: June 13, 2021, 10:10:01 am »
@burkm

First, BG7TBL is supposedly the name/callsign of an amateur radio operator who has designed many, many radio circuits - his GPSDO is just one of these designs.

But it seems BG7TBL is licensing his designs or getting them copied/pirated by a number of different companies, who all sell them under his "brand" BG7TBL. You can only tell them apart when you open them, and the differences are not immediately obvious.

I think worrying about real or fake u-blox GPS modules in a BG7TBL GPSDO bought on eBay, Amazon or AliExpress is somewhat missing the point: these are very cheap instruments that either work within specifications and satisfy your needs, or you should just return them to the seller and buy professional grade (and certainly more expen$ive) instruments.
 

Offline Noy

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Re: bg7tbl gpsdo master reference
« Reply #887 on: June 13, 2021, 03:31:52 pm »
Just a short update i will give some more information later when im not so busy anymore.

The used M8T from eBay is working quite well. Even with the "original" still locked AVR.
The issue was that the GPS module must be configured the right way (NMEA stream must start with the right "talker ID" for GPS)
And it is not possible to enable more than 3 GNSS at once even if 4 are available..

 

Offline burkm

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Re: bg7tbl gpsdo master reference
« Reply #888 on: June 13, 2021, 04:43:30 pm »
@burkm

First, BG7TBL is supposedly the name/callsign of an amateur radio operator who has designed many, many radio circuits - his GPSDO is just one of these designs.

But it seems BG7TBL is licensing his designs or getting them copied/pirated by a number of different companies, who all sell them under his "brand" BG7TBL. You can only tell them apart when you open them, and the differences are not immediately obvious.

I think worrying about real or fake u-blox GPS modules in a BG7TBL GPSDO bought on eBay, Amazon or AliExpress is somewhat missing the point: these are very cheap instruments that either work within specifications and satisfy your needs, or you should just return them to the seller and buy professional grade (and certainly more expen$ive) instruments.

Might be, but they are all sold under the call sign/name of BG7TBL and he probably is the designer (and manufacturer) of those units. I bought mine over the internet through one of the many ebay dealers. But when i contacted him by E-Mail some time ago he never mentioned any other manufacturer. The reason that I question the built-in GPS chips, because most of them available on the Chinese market are fakes or at least "clones". If you look closer at those photos provided here (GPSDO) and the labels going with it, it looks as if many clones/fakes are used in his designs / items too, probably because they are cheap to get. Information on those BG7TBL units are scares, one really doesn't know against what specs the units have to be validated except that the units are somehow "functional". Most of the buyers here don't question the labeled GPS chips, because they just trust, what is been shown, which might not be what they are getting.

I.e. my own unit had all label markings rubbed off except a small left upper hand section with the U-blox trade mark shown, thus no hint what version I got and if it's "real". The label was affixed somewhat slanted and off-center, which never seems to be the case with original units...  8)
If you look around for this on the internet there are lots of videos and articles about this, but - surprisingly - never mentioned / questioned here...
« Last Edit: June 13, 2021, 04:47:45 pm by burkm »
 
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Online AndrewBCN

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Re: bg7tbl gpsdo master reference
« Reply #889 on: June 13, 2021, 04:53:02 pm »
Just a short update i will give some more information later when im not so busy anymore.

The used M8T from eBay is working quite well. Even with the "original" still locked AVR.
The issue was that the GPS module must be configured the right way (NMEA stream must start with the right "talker ID" for GPS)
And it is not possible to enable more than 3 GNSS at once even if 4 are available..

Actually in my experience: the M8T only allows certain combinations of maximum 3 different GNSS, 4 is impossible. Also, having 3 GNSS enabled at the same time is not necessarily a good idea when it comes to timing applications such as a GPSDO. I am using an M8T module with just two constellations enabled (which happens to be the default): GPS and GLONASS. But I suspect the timing pulse is derived only from the GPS constellation, in normal use. When I enabled the Galileo constellation, the M8T took much longer to get a fix - and to generate a stable PPS.

YMMV, of course.
 

Offline syau

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Re: bg7tbl gpsdo master reference
« Reply #890 on: June 13, 2021, 10:44:33 pm »
Anybody succeed to putting a “real” M8T into those units ? The reason I ask is the T family have diff pin out than the “N” or other family (real or fake) they are using.
 

Offline Noy

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Re: bg7tbl gpsdo master reference
« Reply #891 on: June 13, 2021, 11:07:43 pm »
I put a real M8T into my unit. There is no other pinout. Just swapped the fake module to an used M8T from eBay and reconfigured in the right way. Everything works.
 
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Offline Noy

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Re: bg7tbl gpsdo master reference
« Reply #892 on: June 14, 2021, 06:35:39 am »
Attached my final M8T configuration with 3 activated GNSS (GPS,GLONASS,Galileo)
Fix is quite fast I'm located in Germany so there is better Galileo coverage than Baidou..


(remove .hex)
 

Online AndrewBCN

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Re: bg7tbl gpsdo master reference
« Reply #893 on: June 14, 2021, 07:11:09 am »
Attached my final M8T configuration with 3 activated GNSS (GPS,GLONASS,Galileo)
Fix is quite fast I'm located in Germany so there is better Galileo coverage than Baidou..

I would think changing the M8T settings from the factory default makes very little difference, the most important factor is really whether you have a good exterior antenna with an unobstructed view of the sky.

Also, from everything I have read: with a good exterior antenna a much cheaper M8N module works just as well as the M8T in a simple GPSDO design such as the BG7TBL

YMMV.
 

Offline Noy

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Re: bg7tbl gpsdo master reference
« Reply #894 on: June 14, 2021, 11:29:25 am »
You have to change the configuration to get it to work with the AVR in the E-GPSDO Designs..

M8T has builtin TCXO
 

Online AndrewBCN

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Re: bg7tbl gpsdo master reference
« Reply #895 on: June 14, 2021, 12:51:34 pm »
You have to change the configuration to get it to work with the AVR in the E-GPSDO Designs..

M8T has builtin TCXO

Yes, I know, but the TCXO in the M8T module makes no difference when the module is used in a GPSDO: it's the OCXO (and the performance of the control loop) in the GPSDO that matters.

For the BG7TBL GPSDO, I believe replacing the M8N with an M8T provides zero improvement in any measurable parameter, whether it's overall frequency stability, time to achieve satellite acquisition, frequency stability in holdover mode, etc.

Of course I would be glad to be proved wrong, if anybody has the numbers that clearly demonstrate an advantage for the M8T vs M8N in a BG7TBL.
« Last Edit: June 15, 2021, 11:57:00 am by AndrewBCN »
 

Offline Noy

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Re: bg7tbl gpsdo master reference
« Reply #896 on: June 14, 2021, 01:57:43 pm »
Really numbers i don't have.
My Counter is only the DG992 internal one or my SVA1032X  but "subjective" wise i think there is less deviation / jitter since i upgraded to M8T in the "over time" statistics of the DG992 counter. With the fake Module there was more deviation / jitter . But i have also upgraded the antenna to an Beitan one which is "bigger" and has official support for / advertised for all 4 GNSS systems.
Less Jitter ist also advertised from the M8T Module and for 15$ it's a cost effective upgrade to a genuine one. So "it feels better / more trust worthy now" it's like the " placebo effect " you think it must be better now...
 

Online nctnico

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Re: bg7tbl gpsdo master reference
« Reply #897 on: June 15, 2021, 11:28:43 am »
Really numbers i don't have.
My Counter is only the DG992 internal one or my SVA1032X  but "subjective" wise i think there is less deviation / jitter since i upgraded to M8T in the "over time" statistics of the DG992 counter. With the fake Module there was more deviation / jitter . But i have also upgraded the antenna to an Beitan one which is "bigger" and has official support for / advertised for all 4 GNSS systems.
Less Jitter ist also advertised from the M8T Module and for 15$ it's a cost effective upgrade to a genuine one. So "it feels better / more trust worthy now" it's like the " placebo effect " you think it must be better now...
Until now I never considered the bg7tbl gpsdo to have a fake Ublox module. But I have to say that compared to a GPSDO based on a real Ublox module and one from Trimble it looks like the bg7tbl is less stable (measured over 48 hours and using the exact same brand/model antennas). Maybe it is time to crack it open and check; if there is a fake uBlox inside I probably replace it with a real one.
« Last Edit: June 15, 2021, 11:41:08 am by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 


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