-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 24 Dec 2009 at 9:18, David J Taylor wrote:
> > I'd give one of those a try if I could find a UK stockist. > > Importing from US would probably push price up to about > > same as the Garmin GPS-18x_LVC I have which gives around > > 1us offset when given a full view of sky but doesn't work > > at all where I'd need it near my server. > [] > > David > > David, > > I have the GPS18x LVC mounted inside the house, just near the > underside of a sloping roof, and it sees enough RF there to work well > as a GPS server. As it happens, I extended the cable to twice the > length (a long story): > > http://www.satsignal.eu/ntp/FreeBSD-GPS-PPS.htm#usb > > and it still works just fine. So that would give you a 10m run down > to the PC, which might be enough. I would imagine that you could > probably extend the cable to 20m or 30m without a problem (using > shielded cable). So pop your GPS unit as high and in the clear as > possible (inside the house), and run a cable down to the server. > TV aerial in loft stopped picking up from Winter Hill some years ago due to path being obstructed by trees at front. I'm in an old Victorian house that's a lot higher than a modern one. Trees at front and rear partially block the signal path (although gps works through them to some extent during winter months), at rear the trees are maybe 5m higher than roof and next year there might be another 3-5m growth. Cable run out up wall then back in and to ridge would at a guess be over 20m. I think a mast on rear wall will give widest view of sky for longest period and I now have mast and brackets etc, but not yet assembled suitable MSF/DCF receivers or interfaces. I doubt PPS will carry well down coax without suitable drivers and as I need power to units I'm intending using rs422 and twisted pair cables. > Or, put you GPS as high and clear as possible, and add a small > Atom-powered PC and a wireless connection to the rest of your network. > It would probably still beat your 1ms. You /can/ get Atom PCs with a > serial port, but they are less popular than those without. One > example: > > http://www.dabs.com/products/shuttle-mini-itx-intel-atom-1-66ghz-s-l > -v-silver-black-5HFX.html Offsets are degraded too much over 10/100 lan so adding wireless network connection in between can't improve it. I've considered straight wireless interfaces but have no experience with them and they still need power by cables as do the receivers (unless I fitted solar panels on roof with battery for power but that's a lot more expensive than were mast and cables). Intention is to expand PPS and run to each of servers. PPS from MSF via Conrad module gave 50% of offsets within 165us and jitter 70us and maximum offset 621us and jitter 331us but I expect to significantly improve on that for a backup, whilst GPS was about 1us except for when there was signal loss. David - -- David Lord <[email protected]> <ftp://ftp.lordynet.org/pub/pgpkeys/lg_david.pkr> <http://www.lordynet.org/pub/pgpkeys/lg_david.pkr> -----BEGIN PGP SIGNATURE----- Version: PGP 7.0.4 -- QDPGP 2.65 Comment: http://community.wow.net/grt/qdpgp.html iQA/AwUBSzNZKq2RmIodDo7KEQKPIACgnw0qWiAzH4HAeEVMcCjns6FJZLMAoLbt MnRh5UwKBaQSMWfh5Hyf3A4H =E2F6 -----END PGP SIGNATURE----- _______________________________________________ timekeepers mailing list [email protected] https://fortytwo.ch/mailman/cgi-bin/listinfo/timekeepers
