Ghetto 10MHz GPSILTAOALAGKSINS

[purpose]

Afternoon all.

I've been playing around with one of those 5 quid, fake Chinese ublox modules and thanks to theHWcave's video on these units, I now know that anything other than whole number divisions of the 48MHz on board oscillator produces jitter.
So I thought of dividing to 2MHz (which is rock solid, six zeros when locked) and multiplying X5 with an NB3N502 and then band pass filtering.

Would you?

Peter

[Gertjan]

NB3N502 data sheet says: "Output Frequency Range: Min. 14MHz, Max 190MHz".....
https://www.onsemi.com/pub/Collateral/NB3N502-D.PDF

[purpose]

Thanks Gertjan.... I went straight to the small print.

[purpose]

I present the ggpsdo... No distribution, but I've got nothing to distribute it to yet.
Perfect sine wave output.

[bingo600]

Seems like a fun experiment.

But why are you always writing mHz (milli Hertz) , when you mean MHz (Mega Hertz) 

/Bingo

[purpose]

Don't report me to the police... I beg you.

[justanothername]

I present the ggpsdo... No distribution, but I've got nothing to distribute it to yet.
Perfect sine wave output.

I'd really like to see a close up from above.

[purpose]

Best I can do, I'm afraid.

[CJay]

Afternoon all.

I've been playing around with one of those 5 quid, fake Chinese ublox modules and thanks to theHWcave's video on these units, I now know that anything other than whole number divisions of the 24MHz on board oscillator produces jitter.
So I thought of dividing to 2MHz (which is rock solid, six zeros when locked) and multiplying X5 with an NB3N502 and then band pass filtering.

Would you?

Peter

Even an integer division of the internal clock will result in jitter because the correction isn't a nice clean frequency shift, it drops pulses which is great if all that matters is you have the correct number of pulses per time interval, not so great if you're looking for low jitter and not using it to discipline an external 'clean up' oscillator.

[iMo]

I always wonder how the below 30ns RMS translates into the output signal quality (without disciplining an OCXO..)..

PS: you will get the NEO's output with "a not broken jittery signal" when 48MHz is divided by N, where N=4,5,6,7,8,...
The 30nS RMS is a different stuff, however, it comes from above..

[rfclown]

What is the reference on your counter?

[purpose]

I'll have to take your word for that, Clay.
The ublox has visible jitter at anything other than whole number divisions, so no visible is fine with me.
This is after all an experiment for someone (me) that barely knows the difference between resistors and raspberries.

[purpose]

I'm sure you're right imo, but just seeing a nice 10 meg sine come from a 2 meg square was reward enough for my tiny mind.

[purpose]

rfclown... do I have to open it up?

ACT 10.00MHz 9452

[rfclown]

rfclown... do I have to open it up?

ACT 10.00MHz 9452

No. The answer is the internal reference. Some counters allow for an external reference.

[purpose]

This one not.

[CJay]

I'll have to take your word for that, Clay.
The ublox has visible jitter at anything other than whole number divisions, so no visible is fine with me.
This is after all an experiment for someone (me) that barely knows the difference between resistors and raspberries.

They aren't terrible, it really depends what you're using the output for,  were you seeing jitter on the counter at 10MHz?

[purpose]

With the ublox set at 10MHz, was seeing jitter on the scope and the counter was certainly jumping around.
2Mhz was solid on both, so thought I'd isolate the 10Mhz harmonic, but was then seeing instability.
Went for the 5X multiplier and band pass. Rock solid on both scope and counter.

[CJay]

With the ublox set at 10MHz, was seeing jitter on the scope and the counter was certainly jumping around.
2Mhz was solid on both, so thought I'd isolate the 10Mhz harmonic, but was then seeing instability.
Went for the 5X multiplier and band pass. Rock solid on both scope and counter.

Yeah, that's my experience of them too, even on a known genuine U-Blox, integer divisors are a *lot* better and make them useable in a lot of cases.

Worth noting that multiplying it up is a neat trick but does have the disadvantage of multiplying the errors too so the better the signal you put in, the better the signal you get out

Having said all that, I like your project, nicely done

[purpose]

Cheers CJay,
I won't be winning any awards though.

[justanothername]

This actually seems useful enough for me to try to replicate it. I really like the simpleness. Whats the type of the PLL pcb? Can't read it from the picture.

[purpose]

Clock Multiplier Module Frequency Multiplier Module 2-50MHz SMA Interface

Hold on though... The spectrum was much better before I lumped them together, so if you do the same, maybe space them out more and keep the sma stuff.

[justanothername]

It looks cleanly done to me. I propably would omit the series resistor from the ublox module to the PLL board, or maybe use the resistor itself as jumper.
You may want to try to use different power supplies since most of the USB chargers are mostly switched and noisy. And maybe put everything in a metal case.
I don't expect it to be as good as my GPSDO with ovenized crystal, but it is promising, especially if you put everything together onto a cheap single layout this could be made super cheap and may be enough for half of the tasks for an GPSDO.

[CJay]

Cheers CJay,
I won't be winning any awards though.

Nope, you won't but nor would I, I tend to build things like that to get a job done and then chuck them in a box or tear them down.

SMA connectors between boards and some shielding may improve matters but I wonder how good the 2MHz input looks on that spectrum analyser and if it shows the same pattern 'divided by 5'?

If you want to explore and experiment more it's worth thinking about what you intend to achieve and how the different approaches work, all the various 'frequency standards' have advantages and disadvantages, some are great short term, some are pretty awful.

FWIW, it's not that much more difficult to 'discipline' a cheap OCXO and get a really clean signal.

It is however considerably more difficult to discipline it well

[tszaboo]

Is this a GPSDO?
Afaik, those Ublox modules have a TCXO in them, where the 24MHz is not disciplined ( derived/compensated ) with the GPS signal.
The 1 PPS signal is, and you need to use that with the usual controller to make it 10MHz.