The Thunderbolt Trimble GPSDO I ordered finally arrived, after all you can’t possibly have _too_ many time sources.   Of course the first thing I did was set it up, run the position survey and plug it into my HP 5335 Universal Counter which was recently calibrated to a rubidium standard.

Lo and behold after warming up the counter still read:

9.999 999 71 +6   (i.e. 9.999 999 71 * 10E6)

Ok, the trimble will take a while to run the Allan Deviation, I’ll leave it go and come back later.   24 hours later I read:

9.999 999 71 +6

No change, so what’s going on here as I expected exactly (or close to) 10 MHz and I’m reasonably sure the HP Counter is accurate.

I switch to Period mode:

100.000 002 9 -9 (i.e. 100.0000029 *10E-9

Which matches the observed frequency, at 10MHz the period should be exactly 100 nanoseconds…  what’s going on here, lots of fiddling and trying to work out why it wasn’t right, is my counter wrong or there a problem with the Trimble…

What I didn’t facter in is that the ‘002 9′ is in fact ‘2.9 Femtoseconds’ or 2.9*10E-15, the rated accuracy of the GPSDO is 1.16*10E-12.

Aka… timing resolution achieved, and I can forgive the 2.9 femto seconds in either the counter or gpsdo.  In other words, its reasonably accurate as is my counter, and that’s probably as accurate as I’m likely to have… at least until I get my hands on a cesium standard 😉

All I need to do is sit, wait, confirm the results once the GPS has reached its rated resolution, and then use that as my frequency reference.  This will probably take a week or so, but for now it’s not bad.

http://www.vk2vjb.net/2015/08/06/go-back-to-school-nugget/

I spent a little time today getting my GPSDO up and running.  This will be used as my primary reference for microwave work, test equipment, etc.

Project Page

A reminder to all that the annual auction will be held on July 4 2015 at the rose bay club house.   Come along, sell some stuff, buy more stuff, and have a fun day 😉

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https://vk2bv.org/event/club-annual-auction/

I spent a little time today calibrating the desktop CNC mill I’m refurbishing.   A little writeup is available on my site if people are interested.   This CNC will be mainly used to make PCB’s for radio projects 😉

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I spent a little time today in between IT Tasks at work tuning the little desktop CNC I acquired recently. One of the first objectives is to replace the spindle which has an unusual collect design with a more generic ER11 collet so I can use all the small PCB and milling bits I have rather than searching for bits with a 6mm shaft. As part of this upgrade I’ll be moving from the standard 10W DC motor to a brushless RC motor with a little more torque and a lot more speed which is essential when working with small bits.

First up was calibrating the axes, and it turns out the web site I found earlier with the gearing ratio’s on the roland was either incorrect or the one I have is different as all measurements were out by approximately 25%.

A lot of tuning later I have the following (recorded for prosperity):

Step Angle: 3.75 degrees/step
Travel per revolution: 2.36mm (a resolution of 0.02mm)

So the resolution isn’t as good as I’m used to, but sufficient for everything I’ll be using this mill for. There was a little backlash on both the X&Y Axis, which I’ve managed to resolve by tightening the draw wires. I’m really happy I could fix this as the TinyG controller doesn’t actually support backlash compensation.

The tuning took a lot longer than it should have as I kept trying to fix the 0.02mm backlash I was seeing without realising that was the resolution of the cnc… Doh!

With the mill all tuned and adjusted, it was time to follow the age old tradition where the first part cut on the CNC should be a part ‘for’ the CNC. In this case in Wax rather than Delrin so I can verify the sizes and offsets, good thing too as one of the mounting holes is off by 1.75mm.

This also lead to a little bit of Yak shaving where I needed to render the slab of machine wax down to sizes suitable for this mill. I have a nice little pile of wax ingots now, and still have another batch of wax to render down tomorrow.

A quick post to remind people that there is a variety of club merchandise available on Cafe Press. I’ll add a merchandise page to the web site just as soon as I find a cafe press plugin that actually works, in the meantime wander over, have a look, and buy something knowing a little of that purchase comes back to the club.

http://www.cafepress.com/vk2bv

The WARS home page should be significantly faster now as I’ve just switched enabled Amazon Cloudfront for all media files, this provides a very fast front end cache (aka CDN – Content Distribution Network) taking the load off the (small) server we have hosting the web site.

Hopefully this will also help with the occasional ‘stalls’ we are getting due to the current t1.micro instance, which will continue until I migrate the pages to a reserved instance.

If anybody experiences any issues with this, please let me know.

Cheers

Jason.