Author Topic: Where to purchase a cheap GPS disciplined oscillator/Txco 10MHz reference in EU?  (Read 2562 times)

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Offline mcinque

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I'd like to acquire a cheap 10MHz reference (gps or txco) but I can't find any new item shipping from EU except this. I prefer to see the board inside to see its build quality but they show only 2 pictures of the external :(

I found something on ebay built using recycled txco and powered thru a idc header and I don't like very much this solution.

Just to ask if you have any other european website or seller to suggest, I prefer to not purchase from China (import taxes, shipment time).
I'm basically still a rookie and because of this, even with the best intentions, I often say bullshit :)
 

Offline SparkyFX

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Offline mcinque

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Thank you SparkyFX, but I'm looking for a brand new one, already calibrated/tested to be sure that it's a precise reference. Thank you anyway :)
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Offline DimitriP

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   If three 100  Ohm resistors are connected in parallel, and in series with a 200 Ohm resistor, how many resistors do you have? 
 
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Online 2N3055

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The one you showed on SDR kits is Leo Bodnars one...
And is a good quality piece of kit that has additional plus that it has two output that you can independently set output frequency.
So you can use it for more than just 10MHz output.
 
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Offline cdev

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I picked up a nice TruePosition GPSDO on ebay a few months ago for $40 and it works quite well.

There is a thread here on them.

http://www.eevblog.com/forum/projects/gpsdo-loss-of-satellitesfix-troubleshooting/

For the money it was a great deal. As of yet have nothing to measure it with besides WWV and a PIC based frequency counter, but other folks here and on TimeNuts hold them in high regard.

It just chugs along, if you give it a decent GPS signal. Its going to go into a case as soon as I decide on a good one to use.

It deserves a decent case, I think. (Looking for a nice case that will give it a good home, not too large, as the board is not very big, and the board I use to control it and its display are also tiny.)

 It's very well built. Overdesigned for telecom service.
« Last Edit: January 08, 2018, 01:47:17 am by cdev »
"What the large print giveth, the small print taketh away."
 
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Offline mcinque

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I picked up a nice TruePosition GPSDO on ebay a few months ago for $40 and it works quite well.
Found only in China on ebay.it :(

The one you found is this:
Thank you for posting the correct website/shop!

And is a good quality piece of kit
Do you own one of it? Did you see the internal board and how it's engineered? I didn't find any teardown or tecnical review but I assume it's well built seeing the other products he sells. And it's a very nice price
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Online 2N3055

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Do you own one of it? Did you see the internal board and how it's engineered? I didn't find any teardown or tecnical review but I assume it's well built seeing the other products he sells. And it's a very nice price

No, I don't but it is on my TOBUY list...
Quite detailed performance analysis is here:
http://leobodnar.com/files/Informal%20Evaluation%20of%20a%20Leo%20Bodnar%20GPS%20Frequency%20Reference.pdf

It is not perfect but excellent in that price range. And good enough for most people..
Fact is that I couldn't find a single negative opinion...  And Leo is active here on forums and is respected engineer...
I would rather buy it, than some unknown stuff from E-bay..

Regards,

Sinisa.
 
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Offline cdev

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The TruePosition is also very well built.

Some have a Bliley OCXO, others have a different, newer OCXO on them. I have the Bliley model.

They are frequently available on both US and Chinese auction sites. they are based on a Furuno GPS.

Every indication I have seen/read says its a decent choice. The reason you hear so little about them is that they sell exclusively to telecom customers.

All of the data that is out there on them is encapsulated in the threads here and on time-nuts mailing list, ( https://www.febo.com/pipermail/time-nuts ) and on the web site of the "PackRats" ( Packratvhf.com ) club in Pennsylvania.

Eevblog user @pigrew - as well as @texaspyro have both done a lot of research on the HW.

TruePosition is supported by Lady Heather beta version  and @pigrew has written a quite functional controller program for it which runs on the very inexpensive STM32F103 "minimal system development board" (i.e. "Blue Pill") which costs around $3 or less, and a similarly inexpensive OLED display.

This is the page of his code that documents the receiver command set.

https://github.com/pigrew/trueposctrl/blob/master/GPSDO_commandset.h

Texaspyro also managed to extract the ROM from a bord that he had accidentally damaged because a power supply's voltage regulator burnt out.. So he extracted a lot of possible commands.. so the knowledge of the device has steadily been expanding.

Also, there is an older project that implements a controller for it using an Arduino. (but the source last I looked was not available, just the compiled code)

http://www.qsl.net/wa2omy/A%20Packrat%20GPS%20Receiver%20Project.pdf

Also, you can just use RS232 or 3.3 volt UART.

Also, there is another controller implemented via a web style interface for Windows.
https://github.com/don-r/TruePosition-GPS

For completeness here is the previous thread here on eevblog:
http://www.eevblog.com/forum/projects/gpsdo-loss-of-satellitesfix-troubleshooting/

The time-nuts threads can be searched for on Google.. but they don't show up,

https://www.febo.com/pipermail/time-nuts/2017-May/105436.html

https://www.febo.com/pipermail/time-nuts/2017-May/105233.html

https://www.febo.com/pipermail/time-nuts/2017-May/105182.html

https://www.febo.com/pipermail/time-nuts/2017-May/105287.html
« Last Edit: January 08, 2018, 06:12:05 am by cdev »
"What the large print giveth, the small print taketh away."
 
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Offline SparkyFX

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U-Blox sells GPSDO with programmable frequency output and included TCXO.
I mean... once the scope for this is set as GPSDO, you got to live with the limits of the satellite system as reference, way good enough for what i need. As far as i understood you either got a location and a frequency based on the satellite time or not, so once this module delivers a location its internal time standard is ok?
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Offline cdev

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Ublox doesn't sell a GPSDO (if you define GPSDO as I do, which means it has an OCXO - an ovenized quartz crystal or rubidium oscillator disciplined by GPS..)

- Some people confuse timing GPSs with a GPSDO. Timing or non timing GPS has jitter, depending on design and clock speed (Ublox isnt as good as some others there is a predictable quantization error.)  GPSDO with OCXO or OC rubidium oscillator or similar - properly designed, smooths out the jitter a lot.

Thats the whole point of a GPSDO. The GPS in a GPSDO will also typically make some signals available which can be used to correct the oscillator- a feedback loop

For many things, it doesn't matter. If you just want to set an NTP time server it doesn't matter because the network is going to eliminate your precision.
« Last Edit: January 14, 2018, 01:36:18 am by cdev »
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Offline mcinque

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I purchased a Leo Bodnar Mini GPS reference clock, very satisfied for the price.

Look the board inside
I'm basically still a rookie and because of this, even with the best intentions, I often say bullshit :)
 

Offline cdev

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Does it have any issues with spurs on the adjustable output signal(s) with some settings, but not with others?
« Last Edit: January 13, 2018, 11:02:16 am by cdev »
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Offline mcinque

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I tried it at 1, 10, 100, 800MHz at different power levels with no issues. I guess if there are some spurs, I should scan it's entire frequency range to find them and it's quite time consuming since it's a manual setup and can't be automated.
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Offline cdev

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How stable is the frequency without the oven using its TCXO?

Its nice that it has a sine wave output unlike a raw clock gen set up to enable variable output frequency.

I tried it at 1, 10, 100, 800MHz at different power levels with no issues. I guess if there are some spurs, I should scan it's entire frequency range to find them and it's quite time consuming since it's a manual setup and can't be automated.

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Offline mcinque

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Quote
Its nice that it has a sine wave output unlike a raw clock gen set up to enable variable output frequency.
It's the opposite: Its output is not a sine wave, it's 3.3V CMOS with a variable frequency.

Quote
How stable is the frequency without the oven using its TCXO?
I didn't understand correctly your question.
AFAIK, without the GPS lock it cannot output anything by itself. It uses the internal TXCO to compensate GPS losses. "If GPS signal is lost, digital PLL will maintains best estimated output frequency based on historical data. On reacquisition of GPS lock, output is seamlessly brought back in sync with GPS reference. Entry and exit of frequency hold is glitch-less."
« Last Edit: January 14, 2018, 01:48:40 am by mcinque »
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Offline cdev

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[Note: If you totally lose GPS signals its likely we all have bigger problems than not knowing the accurate time, take cover in a basement immediately]

Sounds like a DDS device I have (SI5351) which was quite inexpensive.

https://www.adafruit.com/product/2045

It takes a 25 MHz reference and delivers multiple output square wave CMOs level frequencies. 

https://www.silabs.com/Support%20Documents/TechnicalDocs/Si5351.pdf

Depending on the settings, the signal is fairly accurate. (measured with a $10 PIC frequency counter which contains a TCXO at room temperature, its proven to be very accurate- but not as much when its much colder (or probably hotter too)

Because its signal source is a 25 Mhz oscillator (and not a GPS) its stable. But as it is now its a little bit off and that error is likely temperature dependent.

Its stability is of course dependent on the 25 MHz reference oscillators stability.

Suppose that was derived from a GPS with no means of smoothing it out..

How does the GPS know what signal is accurate unless it can reference it to something stable long-er term? The error is much more marked in the vertical plane than in the horizontal plane..  If I tell it its being used by a pedestrian who is basically almost standing still its significantly better.  Its as good as anything I can measure.

But, I wouldn't multiply it a lot and expect it to remain super accurate at that higher frequency because the error that must be there likely will also multiply.

That said, I bet this device would perform at a higher level if you put it in a temperature controlled box..
---

Okay, lets pretend we are running GoogleEarth in an office on the 25th floor of a skyscraper (so up a bit) and looking at a view in GE as seen from a changing KML file of our "current location". Is the view stationary? or does it look like we are on a boat on a sort of ocean?
« Last Edit: January 14, 2018, 02:48:46 am by cdev »
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Offline cdev

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"Historical data" of what? Referencing what? And how is it stored??

Quote
Its nice that it has a sine wave output unlike a raw clock gen set up to enable variable output frequency.
It's the opposite: Its output is not a sine wave, it's 3.3V CMOS with a variable frequency.

Quote
How stable is the frequency without the oven using its TCXO?
I didn't understand correctly your question.
AFAIK, without the GPS lock it cannot output anything by itself. It uses the internal TXCO to compensate GPS losses. "If GPS signal is lost, digital PLL will maintains best estimated output frequency based on historical data. On reacquisition of GPS lock, output is seamlessly brought back in sync with GPS reference. Entry and exit of frequency hold is glitch-less."


@CJay explained it well in this post:
http://www.eevblog.com/forum/projects/gps-locking-a-tcxo-that-drives-an-si5351/msg1085722/#msg1085722

https://qrp-labs.com/ocxokit.html
« Last Edit: January 14, 2018, 02:46:03 am by cdev »
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Offline mcinque

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Quote
Referencing what?
I guess the atomic clocks all the GPS satellites have, which are in sync with each other GPS satellite and with the stations on earth.
They sends specific timestamps via radio signal: for navigation you obtain your position on earth by knowing satellite numbers, their positions in orbit and precise time delay between each radio signal. For time/clock syncronization I guess you use the timestamps as a precise time reference. Someone correct me if I'm guessing wrong.

Quote
"Historical data" of what?
I guess of the GPS signal timestamps.

Quote
And how is it stored??
Of course by writing in the 256 Bytes of integrated EEPROM of the PIC.
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Offline cdev

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Your .sig also applies to me, so with the caveat that I could easily be wrong, its my impression that we really can't be as precise as we would hope for without "the averaging function" implemented in some robust way, with GPS.

Because the ionosphere, temperatures changing, tidal forces changing the gravity minutely,  and things like that.

Think of the simplest aspect of GPS as simply a set of clocks very precise clocks synchronized to one another in space. And then they stream it over radio, using a technology that let even very weak signals be pulled up out of the noise, (its typically below the noise!) by the magic of statistics.

At precise intervals that streamed time as broadcast by the satellites in view is recorded, bang, bang bang. and from that (and trigonometry) is derived the distances to them at that instant.

Then the position of those satellites at that instant is known to an arbitrary precision we then can get the time back, minus some variability which also can be calculated.

All the errors add up. One error that changes a lot is the ionospheric factor which to me seems similar to the waves on an ocean and which seems similarly unpredictable.

However if you have a stationary "base station" nearby you know the position of, and you can combine -subtract its position from your data stream you get a difference figure that is more accurate positionally.  Similarly if you know that you yourself are stationary, and the GPS can be told exacly where it is and store that (One way of doing this is called  "TRAIM" thats probably what your GPSDO is doing)

With TRAIM you can get a substantially more accurate signal than otherwise for timing purposes.

How does it work? Your GPS is stationary and you know that, and can tell it that,

It itself then using statistics can figure out the location in a way that (should) get steadily better the longer it is turned on. But at some point (which should be a long time, >24 hours is optimal) it reaches a point of diminishing returns.

THEN say its figured out where you are -and has stored that position..and the signal is very good, then it can give you a timing signal that it knows is quite accurate. verifiable quality. It only needs one satellites signal at that point, to do that.

But anyway, all GPS's fine tune their internal settings to give you the best possible solution that's available given the information that they have available. 

Just using ephemeris data that the satellites themselves provide that may be very good.


You can get timing accuracy to under ~100 nanoseconds from virtually all good GPS devices - but that accuracy can easily be lost in the signal chain - after it leaves the GPS, for example, interrupts and the servicing of them. Or the cable delay which should be stable, that you can compensate for.

Many GPSs are substantially better than that, but the accuracy they claim is only under ideal other conditions which dont exist in the real world.

There is this substantial variability due to these other factors which is unavoidable but which does occur in somewhat predictable ways.

Those same things would effect timing. You can minimize one of them, multipath, by setting a very high elevation mask and using an antenna that rejects the wrong polarization, no-matter what direction its coming from (because signals that are reflected once are reversed polarity).

But even if your setup is totally optimal to do much better, orders of magnitude better, you need a way of averaging the time out - over time. You can get another order of magnitude or maybe even two fairly easily, by disciplining an ovened quartz oscillator. That's still much better than anything we could do as little as 25 years ago. Even if your device has the best GPS signal there are things which it may be unable to cancel out which could be improved on by thermal controlling its environment.

Also, barometric pressure influences crystal oscillators measurably.

Still where we are now is a pretty amazing place.

You may be able to get better performance by controlling your oscillators temperature precisely. I don't know. But you may not need that now or in the near future, whats the point?

If your device does what you need it to do, gives you a precise, plug and play source of different frequencies for testing, it was likely a better choice for you than an ovened GSDO.

I know I don't need that level of precision in anything I currently do, yet.

But I hope to eventually. Many applications, for example in telecommunications, need more. 

The more mileage they try to get out of the spectrum, the more timing precision they'll need.

So I figured I could use it someday, maybe.
« Last Edit: January 14, 2018, 05:01:01 am by cdev »
"What the large print giveth, the small print taketh away."
 

Offline Squiddaddy

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I have one of these coming any day now. It is the 2010 version with the CTS OCXO on it.
It will be interesting to get the pinouts correct since it doesn't match the PackRat docs at all.
I finally got sucked into the GPSDO world. LOL  :-DD



The TruePosition is also very well built.

Some have a Bliley OCXO, others have a different, newer OCXO on them. I have the Bliley model.

They are frequently available on both US and Chinese auction sites. they are based on a Furuno GPS.

Every indication I have seen/read says its a decent choice. The reason you hear so little about them is that they sell exclusively to telecom customers.

All of the data that is out there on them is encapsulated in the threads here and on time-nuts mailing list, ( https://www.febo.com/pipermail/time-nuts ) and on the web site of the "PackRats" ( Packratvhf.com ) club in Pennsylvania.

Eevblog user @pigrew - as well as @texaspyro have both done a lot of research on the HW.

TruePosition is supported by Lady Heather beta version  and @pigrew has written a quite functional controller program for it which runs on the very inexpensive STM32F103 "minimal system development board" (i.e. "Blue Pill") which costs around $3 or less, and a similarly inexpensive OLED display.

This is the page of his code that documents the receiver command set.

https://github.com/pigrew/trueposctrl/blob/master/GPSDO_commandset.h

Texaspyro also managed to extract the ROM from a bord that he had accidentally damaged because a power supply's voltage regulator burnt out.. So he extracted a lot of possible commands.. so the knowledge of the device has steadily been expanding.

Also, there is an older project that implements a controller for it using an Arduino. (but the source last I looked was not available, just the compiled code)

http://www.qsl.net/wa2omy/A%20Packrat%20GPS%20Receiver%20Project.pdf

Also, you can just use RS232 or 3.3 volt UART.

Also, there is another controller implemented via a web style interface for Windows.
https://github.com/don-r/TruePosition-GPS

For completeness here is the previous thread here on eevblog:
http://www.eevblog.com/forum/projects/gpsdo-loss-of-satellitesfix-troubleshooting/

The time-nuts threads can be searched for on Google.. but they don't show up,

https://www.febo.com/pipermail/time-nuts/2017-May/105436.html

https://www.febo.com/pipermail/time-nuts/2017-May/105233.html

https://www.febo.com/pipermail/time-nuts/2017-May/105182.html

https://www.febo.com/pipermail/time-nuts/2017-May/105287.html
 

Online DC1MC

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Me as well, I've splurged for a True Position with a Bliley OCXO. Are there any reasonable priced compatible antennas available in Germany ?
How can you make a square wave low jitter, do I really need the Rubidium one as well (rethorical question ;) ?

  Cheers,
  DC1MC
 
 

Offline Squiddaddy

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I got my TruePosition working somewhat. Still finalizing it.
Mine has an issue where the TTL serial pins do not work properly, so I have to use the RS232 port. I think I damaged it with a faulty Chinese USB-TTL adapter that was suppose to be 3.3v but hit it with 4.2v. won't receive commands anymore.
Had to add a MAX232 chip to the AtMega328 Arduino to get the serial data.
I have the 2012 version with the CTX OCXO and version 12.1.1 firmware. 2 10MHz ports and a 1PPS port.
It also works fine with the puck antenna I got with a uBlox.
But I bought a Lucent timing antenna for $40 from Ebay. Never goes into holdover with that one. :)
I am working on an Arduino program to control it and display data on an LCD.
Working good now, but I need to write conversion routines to get the date and time from the stream. Got time working, but date is a pain.
Once done, I will put an Atmega328 and a MAX232 on a board and get it into an enclosure.
 


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