How to manage a 1 Hz frequency with a PLL?

[gusagar]

Hi friends.

I need to build a good frequency reference and am thinking about to lock the one hertz out (1 PPS) from an OEM GPS module to a good VCO (crystal) oscillator, but have no idea about how to manage that so low freq. with a PLL. The 1Hz reference is easy to obtain with some dividers from a 1 MHZ TCXO, but I ignore what will be the PLL behavior comparing and managing 1 Hz!

Have any of you an idea to solve this, Thanks in advance

Gustavo:idea:

 

[toonafishy]

homemade pll

**broken link removed**

 

[gusagar]

gpsdo

Thanks toona.

The Shera´s solution is very smart but uses parts almost impossible to find, like de DAC, really I´m looking for something simpler.

Thanks again

 

[sergio mariotti]

cw12-tim

Me too had the same idea!
To build toghether a GPS module and a surplus VCXO to get a long time accurate clock.
But unfortunately it works fine only with numeric circuitry.

The GPS is provided by a 1pps out signal.
On the market You may found only "disciplinated-oscillator" that uses 1pps , but not PLL locked to 1 pps.

I suppose the reason is related to the amount of phase noise.

Since the phase noise (at distance from carrier where the loop noise dominate) is almost 20log N , if N is very large (as it's this case) the output phase noise will be not competitive.

The disciplinated oscillator, as classical PLL, generate an error signal which is proportional to the difference between REFerence clock and VCO , but for very slow phenomena, the "phase difference" became "time-delay".
The delay is intimally numeric (so less noisy) while the phase is intimally analogic (so affected by noise). This is the reaseon because performant disciplinated oscillator uses numeric ciruitry.

Do You want know what I've made?
Instead spend time and money into an homemade solution I've spent a similar amount of money into a second-hand, cheap, Rb-vapour oscillator.

 

[gusagar]

pll gps pps module

Thanks so much Sergio.

Now I understand why all the articles I read talk about "disciplinated", oscillator. Please let me know what was your numeric solution. The rb solution is the logical one but I imagine it isn´t cheap. I have found some GPS´s in the web with a 10 Mhz disciplinated output but I dont know if I can "trust" on them, in this address you will find the .pdf of the one I think can be used as the freq. reference I´m looking for. Please take a look and let me know what do you think. This module was quoted to me for US$ 130.76.

**broken link removed**

The Brooks Shera´s disciplinated solution looks atractive too, but how can I know my "clock" can be used as a true reference?, I have no mean to compare my final work with a rb or H reference, so I must be sure what am I doing

**broken link removed**

Thanks again for your valuable contribution and for your time

Gustavo
(Colombia)

 

[sergio mariotti]

pll pps

Thanks so much Sergio.

Now I understand why all the articles I read talk about "disciplinated", oscillator. Please let me know what was your numeric solution.

As "numeric" I mean the measurement performed by a digital counter.
The readout will be used to correct the XO.
The correction may be done in analog way, by D/A conversion then driving a VCXO.
Alternatively, the correction may be done in a fully digital way by adding or deleting one or more 10MHZ ticks.

The rb solution is the logical one but I imagine it isn´t cheap.

around $200 on ebay

I have found some GPS´s in the web with a 10 Mhz disciplinated output but I dont know if I can "trust" on them, in this address you will find the .pdf of the one I think can be used as the freq. reference I´m looking for. Please take a look and let me know what do you think. This module was quoted to me for US$ 130.76.

**broken link removed**

I think it's very performant device, It's great the possibility to set the Out. frequency.

Since I read now that You will use the oscillator as frequency reference, (i.e. not epoch reference) , I suppose the phase noise may be important to You.
Really speaking, most high performance XO are less noisy than RbO.

The Brooks Shera´s disciplinated solution looks atractive too, but how can I know my "clock" can be used as a true reference?, I have no mean to compare my final work with a rb or H reference, so I must be sure what am I doing

**broken link removed**

If you have no possibility to compare the GPSDO vs a similar one, You may compare the 10 MHZ OUT freq. with another common XO.
Wait the XO will be thermally stable.
Plugging the 2 signal into an X-Y oscilloscope and see how the circle is stable while change the temperature of the GPSDO ( i.e. heat it with your hand).
If You don't see any drift due to GPSDO, it means that it's now disciplinated so it's trusted