On 2014-01-03 03:54, Ralph Aichinger wrote:
I am currently in the process of remodeling my house and a dedicated outdoor/roof mounted GPS antenna would be possible to mount without excessive cost. I probably would not see a huge difference for timing purposes, but what would your choice of an outdoor GPS antenna/receiver be? I am planning to put the NTP server (small Raspberry Pi, nothing fancy) into a rack maybe 10 metres of cable length away from the roof. Or would you move the NTP host itself to the attic and run Ethernet up? I suppose something like the Garmin GPS 17x (mast mount GPS with serial output and PPS, intended for the marine market) would work fine, also be robust enough and cheap on the used market. Would mounting just an antenna (active or passive) also make sense, or would cable loss be too high? What would *your* roof top setup be? Cost is of course an important consideration, on the other hand, 100 or 200 Euros for the GPS, antenna and mounting hardware is probably OK. I would prefer to do cabling jobs now, while I am in the process of doing a lot of "dirty" things. Or would you not bother at all, and just put some puck into the window (which probably works too)?
You may not be safe running your Pi in an uninsulated attic, as most chips are rated for commercial operation from 0-70C, which could be exceeded in cold winters or hot summers, due to heat buildup in the attic plus device self-heating. All Garmin GPS models are rated for -30C-80C so should be okay outside. Most 17x models, other than 17x NMEA 2000, are not high sensitivity so require clear sky all around, as would be expected in marine use, and those other models appear to be discontinued and replaced by high sensitivity 19x. Marine model power varies by model - LVS takes up to 6V and HVS 9-16V (battery). You could get a new 18x LVC for US$60 + shipping + customs from gpscity.ca (cheapest I found) and crimp or solder the GPS leads and USB (or other 5V) power connector leads into a DE9F. Instructions are on David Taylor's site at http://www.satsignal.eu/ntp/FreeBSD-GPS-PPS.htm#usb I simplified the wiring shown in the above link by connecting all +5V power leads to pin 6 DSR. The page above also has a link to an alternate source of the device already wired to a DE9, with an extra cost USB power adapter, total cost US$100 + shipping + customs. The page notes that Dave Hart bought and used these devices. -- Take care. Thanks, Brian Inglis _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
