Hi Since we are talking about an L1 / L2 antenna here, a reasonable assumption would be that the target is something better than an “average result”. If you construct a cover out of a piece of PVC pipe (as shown in the original drawing), your worst case path has a foot or so of PVC in it compared to a best case path with well under a tenth of an inch. That’s going to give you a bit of variation ….. Add some dirt or water or ice to the equation and who knows what the result might be.
Bob > On Feb 6, 2018, at 3:45 PM, Michael Wouters <michaeljwout...@gmail.com> wrote: > > I can see why the geodetic community would worry about antenna phase centre > variation when a radome is installed but is it really an issue in timing > applications? The few papers I've read suggest PCVs of less than 10 mm, or > equivalently, 30 ps. This is at the level of precision available from > post-processed, carrier phase time-transfer but invisible in the 1 pps > coming out of your receiver, even with a good sawtooth correction. Am I > missing something? > > Cheers > Michael > > On Wed, 7 Feb 2018 at 4:14 am, Bob kb8tq <kb...@n1k.org> wrote: > >> Hi >> >> There are “cell site” specific GPS antennas on the market. Panasonic has >> had one out >> for quite a while. I’m sure there are several others. >> >> One issue with doing any sort of “cover” for a precision antenna is >> distorting it’s pattern. >> Plastic (or whatever you use) will have different properties than air. A >> path through a blob >> of “not air” will change the effective path length. That impacts the >> timing and thus the >> navigation solution. If you are worried about 2mm sort of pattern >> accuracy, things get >> tricky. Early on, there was a big “throw out the radomes push when this >> was first noticed. >> >> Bob >> >>> On Feb 6, 2018, at 6:15 AM, Bo Hansen <timen...@rudius.net> wrote: >>> >>> Hi >>> >>> Besides the RF characteristics it may also be worth considering the >> quality of the plastics used. Over time water ingress may become an issue. >> Fours years after the installation of a CN brand antenna, sourced locally >> so probably not counterfeit either, we had to replace it at OZ7IGY >> www.oz7igy.dk >>> >>> RF wise 42 dB of gain IS an issue. Again at OZ7IGY, with 12 carriers in >> the air especially 13 cm and 23 cm, blocking and IMD were an issue before >> we mounted a BPF. I have taken apart the above mentioned antenna, a >> Motorola antenna and an eBay "hockey puck" antenna. The best design was >> clearly the Motorola one because it had a BPF after the pre-amp - probably >> because it was designed by RF competent people too. Each of the other ones >> had two FETs/MMICs in series and then a BPF. Of cause if no nearby carriers >> are in the air it may be less of an issue. >>> >>> So designing a really good antenna and pre-amp may be a business >> opportunity. There are many hi IP3 MMICs available designed for GPS and the >> like purposes. SAW BPFs with <1 dB loss are available fairly cheap so one >> before the FET/MMIC with a 1 dB NF is the way to go. A DIY radome using >> standard materials from any hardware shop is attached. >>> >>> Bo, OZ2M >>> >>> <GPSAnt_DIY_Radome.png>_______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.