Electronics > Metrology

Cheap GPSDO Buying Help 2024?

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EvgenyG:
Hi, Leo. Just received the new gen LBE-1420 unit, very happy customer. I've done some extensive research comparing the specs against the bigger A brand units and cheap no-name units and decided that it is absolutely worth extra $100. it is hard to beat that phase noise figure at that price point. I think most people don't understand the importance of phase noise. Good to know that there is NMEA support now, I was actually going to ask. Perhaps worth adding that to the product description page as well as brief information what different LED states mean.
Also wanted to note that the build quality is amazing.

dietert1:
In order to get best results, the antenna makes a big difference independent of the GPSDO device. I mean a good antenna installed on the roof with a full free sky view can be difficult to obtain and will by far exceed the cost of the device. A geodesic antenna meant for measurements can be US$ 500 or more. One also needs to think about a good RF cable if it needs more than 5 or 10 m. Or place the GPS receiver next to or inside the antenna.
Once you use a patch antenna inside a building, the GPSDO device won't make a big difference.
Leo Bodnar's stuff is excellent but the LBE-1420 isn't exactly a GPSDO. Instead of adding some fanout for the 10 MHz it adds a wide band signal generator 1 Hz to 1.1 GHz. It can certainly be configured to output 10 MHz with low phase noise and one could try a splitter to sync two or three devices. Don't know if one can run two devices from one antenna, in case one needs 10 MHz and 1 MHz.

Regards, Dieter

Edit: Ours looks like this. Will replace it by a GNSS antenna.

kevin.gibbs:
Does your frequency meter measure the period? If so, you can feed the 1PPS signal from the GPS receiver directly to the frequency meter input. You can also enable averaging (to filter receiver jitter). This should already be sufficient for your accuracy.

You can also take the signal from the MAX4016 input and use it.

NT0Z:
Kevin -- thanks.

My HP counter can measure period, but I have never done so or made period measurements with any other devices.

After abusing the trimmer pot in the GPSDO (who knew that was a trimpot?) I have the sine and square wave output squared away as shown in the dual-trace photo. I am in the process of building a 10-MHz WWV receiver (TRF-style) so I can compare my GPSDO signals (on the scope) with those from WWV. After wrenching on the GPSDO and replacing two SOIC chips, I want to have another NIST-reasonable reference to make sure everything's okay.

I have a "TCXO in a box" that's been reading 1.2-Hz low at 10 MHz for several months. At least it's stable! In the interim I acquired a pair of inexpensive 10-MHz OCXOs, and if my counter is indeed disciplined correctly, each is reading 1.2 to 1.3 Hz high (no more adjustment range). One of the OCXOs will go into an insulated box and pretend to be a rubidium standard. :)

Using the WWV receiver I can feed a 10-MHz signal into the counter or into the scope that's 1 Hz or better at 10-MHz (avoiding dawn and dusk as appropriate) to at least verify that my GPSDO is locked onto the correct frequency...

I will also try the "zero beat" method over the weekend.

Regards,

--NT0Z

SCSKITS:
Any of the inexpensive GPS modules should be able to produce better than 1Hz at 10MHz.
I ran a NEO-M9N on a MIKROE-3922 board (about $39 at Mouser) at 4MHz and got about +/-0.75E-8. At 10MHz, +/-1Hz would be +/-1E-7
A simple multiplier like the PT7C4511 set to 2.5 would give a 10MHz output.
The PTC4511 is in an 8 pin SOIC for easy soldering.
The frequency difference would be multiplied up also (by 2.5)  to less than +/-2E-8 assuming the PLL filter in the multiplier chip had little effect on the error. 
It looks like the 4MHz is getting better over time, I would have to run for a longer time to see just how stable it becomes.
If running the GPS module alone at 10MHz, the error will be greater than with the 4MHz output followed by the multiplier.
I have a test board that has the multiplier followed by a divide function that can be bypassed, I will try to get a run with that maybe over a longer time.

Another option is the LEA-M8F. It is more expensive but is one of the UBLOX timing modules and should do better than the NEO-M9N.
The 30.72MHz output is about +/-1E-9 right after startup, I did not run for a long time. I did not try the programmable output yet.
Starting with 30.72MHz output, you would need a more sophisticated multiplier divider such as the SI5328C which also requires a micro to initialize the part.
The SI-5328C is also difficult to solder for a DIY project.

ed
 

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