Re: NEO series GPS modules

Andy G4JNT

Instead of this rush for GPSDO based references with dubious short term stability, why not go for one of the several really good 10MHz OCXOs that have appeared recently or even a Rubidium source.   There are several Morion types out there, all capable of resetting to within a few parts per billion after a quite rapid warm up.

I have one in the 10GHz PortaBeacon that settles within a couple of tens of Hz (at 10GHz) within 5 minutes of switch on from cold - always.  And that module is an older generation OCXO  - later ones are better still.

Then use a basic GPS module with its 1 PPS output as the reference just for a frequency counter to confirm your calibration from time to time.

Best of all, get a Rubidium source - there are a few around on Ebay for £100 or so.   Not the cheapest option, but that will guarantee you sub PPB accuracy within less than 20 minutes of turn on.  

GPSDOs may be cheap, and although I've never tried these GPS modules being talked bout here, do get an uncomfortable feeling that unless used with a very narrow loop bandwidth locking up a reference, they won't be all that nice when multiplied up to the higher uWave bands.

Unless someone knows better, and has done so ?

Andy  G4JNT

On 26 July 2016 at 15:04, usuallyqrt@... [ukmicrowaves] <ukmicrowaves@...> wrote:

I think users will find with the basic NEO types of GPS modules if you look at the output with the scope referenced against a truly stable source, not another GPS,  that the output signal has a number of discrete phases so is unlikely to be useful directly but might be ok with further integration.  I have not looked at the timing version which ought to have this issue fixed ?

This is much like the phase shifting of Droitwich locked references which many seemed not to be aware of in simple designs.

Good investigation is required before implementation.  The scope must be externally locked or its trace will simply follow the meander.

73 John G8ACE

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