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

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 <timenuts@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.

Hi Indeed a radome may distort the antenna pattern. In teh case of DIY projects the trick that most can apply is to take a piece of the radome material and put it into a microwave own. If it doesn't get hot it is OK for most DIY cases. Infinion have some nice GNSS MMICs e.g. BGA924N6 <http://demo.21dianyuan.com/infineon/download/download_down/id/40/type/cn> Bo

In a previous job, I used plastics to "lens" antennas at 2.4 GHz, shaping the patterns for more desirable results. XFDTD is a great software package for this application but it is expensive.

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 <kb8tq@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 <timenuts@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. >

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 <michaeljwouters@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 <kb8tq@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 <timenuts@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.

That does represent a limiting case but it's a bit pessimistic. The longest path is for very shallow incident angles eg a 3 mm thick and 150 mm radius disk gives an angle of only about 1 degree. At 10 degrees, the path is about 20 mm; with a refractive index of 1.5, the path is only 10 mm longer. 10 degrees might be what you set in the receiver's elevation mask. A mm thick layer of dirt is just going to be roughly another mm of plastic; worse if it's absorbed moisture, true. You have a point about water. Water has about 10 times the refractive index of plastic (real part of n) so this is more of a worry. A 1 mm film will have triple the path through a nominal 3 mm of plastic so at 10 degrees incidence there is now about 40 mm extra path which you might see in post-processing. But you're not going to see that in the 1 pps. Cheers Michael On Wed, 7 Feb 2018 at 8:14 am, Bob kb8tq <kb8tq@n1k.org> wrote: > 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 <michaeljwouters@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 <kb8tq@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 <timenuts@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. >

-------- In message <CAGP4rdm0GbEfr=uWtWq75nmN0Rk05xAUa4v0xdiX9MxR7Dde9g@mail.gmail.com>, Michael Wouters writes: One thing about Bo's pipe radome which is worth pointing out is that like me he is on 56 degrees north latitude, which just so happens to mean that we have no GPS satellites passing directly overhead. I can't remember the exact dimensions of the "hole" we look up into, but eyeballing Bo's sketch, I think the endstop might just never get in the way of any actual signals. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.

Hi It’s not the end stops that are the issue. It’s the wall of the pipe. If the dimensions in the sketch are roughly correct and you scale it to the dimensions of the eBay antenna, that is a big tall pipe. Indeed “nothing overhead” would mitigate part of the issue. That magic line runs roughly along Hadrian’s Wall in the UK. I’d bet that 80 degrees overhead would still be an issue. Again, this is an extreme case and not the typical cover for a GPS antenna. Water wise, one might note the large piles of snow sitting on my antennas at the moment. Yes, I could go knock it off, but somehow it just keeps coming back. Weird how winter works …. There is no perfect solution. Bob > On Feb 7, 2018, at 3:59 AM, Poul-Henning Kamp <phk@phk.freebsd.dk> wrote: > > -------- > In message <CAGP4rdm0GbEfr=uWtWq75nmN0Rk05xAUa4v0xdiX9MxR7Dde9g@mail.gmail.com>, Michael Wouters writes: > > One thing about Bo's pipe radome which is worth pointing out is that > like me he is on 56 degrees north latitude, which just so happens to > mean that we have no GPS satellites passing directly overhead. > > I can't remember the exact dimensions of the "hole" we look up into, > but eyeballing Bo's sketch, I think the endstop might just never > get in the way of any actual signals. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > phk@FreeBSD.ORG | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > _______________________________________________ > 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.

-------- In message <875E4BC6-32C3-4724-AFCD-086553AE52C6@n1k.org>, Bob kb8tq writes: >Water wise, one might note the large piles of snow sitting on my antennas at the moment. Yes, I >could go knock it off, but somehow it just keeps coming back. Weird how winter works …. There >is no perfect solution. Somebody at BIPM told me that their antennas were heated and thermostatically kept at constant temperature. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.