Lars DIY GPSDO with Arduino and 1ns resolution TIC

[thinkfat]

Johnny, I will be interested in hearing how much improvement a Sparkfun ZED9T makes over an M8T. My own Lars build (Murray Greenman, ZL1BPU, display variant), is at the limits of what I can measure in terms of short term stability.

If you're interested in short-term stability of oscillators, you can do a lot with the "tinypfa". For cheap.

https://www.tinydevices.org/wiki/pmwiki.php?n=TinyPFA.Homepage

[Johnny B Good]

@Solder_Junkie

 Whilst I'd love to answer your questions in detail and the information is relevant to any design of DIY gpsdo project, I think it would be better to start a separate topic thread rather than completely hijack this one (I can post a link here for anyone interested), However, as a 'teaser', assuming you haven't already seen this YouTube video, have a look here

@thinkfat

 Thanks for the links to the TinyPFA. ISTR Solder_Junkie mentioning this gadget a month or two back. I checked it out but being the cheapskate that I am (says he who blew 250 smackers on that Sparkfun module some 14 months ago ) I was looking for the cheapest option and gave up on making sure of getting the exact right version to convert. However, money isn't everything so, for the sake of my much put upon SDS1202X-E, I'll pick one of those sources in the list whether pre-loaded or not with the SW. I've been hankering after a means to record the data for a while now anyway (you know how it is - not enough round tuits).

[iMo]

..
I haven't experimented with increasing the smoothing caps on the oscillator Voltage control line, I note that Murray used 22uF caps against Lars using 4.7uF. I use 10uF. If you refer back to the James Miller "Simple" GPSDO, James uses a 160K resistor and 100uF cap to smooth the control Voltage line and achieves around +/-5 parts in 10^11 over a 10 second period. Maybe a larger capacitor would work just as well as going to a more expensive GPS module?..

The precise finetuning of the filter is not an easy task, imho. I made an excel tool, trying to ease the filter design for Miller's XOR based GPSDO in past, posted here.
https://www.eevblog.com/forum/projects/gpsdo-with-xor-phase-comparator-control-loop-filter-design/msg3458070/#msg3458070

[Johnny B Good]

Johnny, I will be interested in hearing how much improvement a Sparkfun ZED9T makes over an M8T. My own Lars build (Murray Greenman, ZL1BPU, display variant), is at the limits of what I can measure in terms of short term stability.

If you're interested in short-term stability of oscillators, you can do a lot with the "tinypfa". For cheap.

https://www.tinydevices.org/wiki/pmwiki.php?n=TinyPFA.Homepage

 I've just ordered one from Mirfield Electronics in the UK.

[Solder_Junkie]

Martin (G3ZXZ) of Mirfield is really good to deal with.