Thursday, November 2, 2017

Paradise ponders: rooftop antenna and Raspberry Shake edition...

Paradise ponders: rooftop antenna and Raspberry Shake edition...  Yesterday, with some help from my brother Scott, I got my GPS antenna mounted on top of my barn.  This antenna is part of my stratum 1 NTP server project.  The antenna is very near the peak of my barn's second floor roof, about 26 feet above ground level.  Prior to going up to the roof, I had mounted a section of 2x10 on the inside of the barn, between two of the roof trusses.  This provided a sturdy mounting point for the antenna, instead of the 1/2" OSB that the roof is sheathed in.  Yesterday I crawled out of a second floor window onto the first floor roof, then put up a ladder to the second floor roof.  Scott and I lashed this ladder to a board placed across the window frame, to keep the ladder's feet from slipping down the first floor roof.  This part worked surprisingly well.

I did some careful planning to fill a bucket will everything I might need while working on the roof.  This almost worked. :)  It turns out I forgot an adjustable wrench, so I had to come back down once for that.  Otherwise, the entire installation went smoothly out of the one bucket full of tools and parts.
The trickiest bit was sitting on the 25% pitched roof without sliding off the slippery steel.  My roofers told me that they often worked barefoot, as their feet didn't slip nearly as much as their shoes did.  I tried this, and it worked just fine.  The walk from the ladder (at the roof's edge) to the peak (where the antenna was going) was maybe 15', definitely a tense distance, though short.  Had I slipped and fallen, I'd have gone off the second floor roof, bounced onto the first floor roof (same pitch), and slid off the side of the barn from about 15' high.  I was quite happy to have avoided this!  While I was doing the actual installation, I straddled the peak of the roof, so I was quite stable.  It was only that little journey from the roof's edge to the peak, and back, that was slightly terrifying.

Naturally I forgot to take photos of this little adventure.  I was too busy trying not to fall off of my barn's second floor roof!

Once I had the antenna installed, I connected it to my little Raspberry Pi GPS board and started testing.  On the first try, we had 12 satellites visible.  A few hours later I had 17.  My time accuracy is now reporting at +/- 2 nanoseconds – not bad at all!  Best of all, after 12 hours of operation the GPS was reporting very high time and position stability – and this is before I've even configured it in a way optimized for timekeeping!

I still have some work to do on the NTP server project, but at this point its all fairly mundane stuff  The C program I'm working on will form the heart of an NTP server monitor that I'll install on the Raspberry Pi.  This will keep statistics on the accuracy over time.  Then I need to build a little cabinet for the Raspberry Pi, so it can take its place of honor on my server rack. 

Just by coincidence, yesterday I also received my Raspberry Shake 4D - a seismograph that reports into an international network.  I assembled it and plugged it in, mainly to see if it was working, and it all seems to work just fine.  I'm not sure where I'm going to mount it – it needs to be on the ground floor, preferably on the concrete slab, and somewhere with minimal vibration and noise.  It might end up going in the basement of my home.  The screenshot at right is off the Raspberry Shake network's station view.  If you click to embiggen it, you'll see the little orange triangle NE of the Great Salt Lake that represents my station – the only one for a few hundred miles in any direction.  Unlike the USGS seismograph that I had in California, this one's data is directly accessible – there's a network API that will let me download it.  You can be sure I'll be playing with that!

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