[time-nuts] Rooftop antenna and splitter

[Bob kb8tq]

Hi

True indeed and for about $10,000 you can get pretty close to “the best”. If you
want to slum it, you can get “pretty good” for about $2,000.  If you are truly 
after high end performance new is the way to go. Getting the full  modern suite 
of signals on a used one …. not so much. Even getting a used one that isn’t a bit 
beat up may be a challenge. I have also seen used antennas listed for more
than they cost new …..

Since all that “best” stuff applies mainly to survey work, it’s not clear that 
one needs to spend that much for a timing antenna. In the context of 
what’s coming, you do very much want all the bands / all the signals /
all the services. That will matter, even for timing. At the very least the European
system should be a great timing source (as GPS already is). The Russian 
system keeps getting better. I have not seen a lot of papers showing the 
Chinese doing quite as well. I’d bet they will catch up if they have not
already. 

Why is best different for survey vs timing? For a good survey, you want
sat’s spread out all over the sky. That quickly gets you to sats that are
close to the horizon. Multipath it going to be an issue when you do that. 
For timing (with a well known static location of course) your best sat’s 
are straight overhead. (the path through the atmosphere is shorter, the 
path is easier to estimate / correct ). You set things like an elevation mask 
to toss out the sat's likely to give multipath. 

Lots of variables ….

Bob

> On Jan 27, 2019, at 9:24 AM, Bill Slade <slade_bill at hotmail.com> wrote:
> 
> Hi again,
> The very best GNSS antennas tend to be based on suspended patch antenna 
> (air-dielectric) structures because they give the best 
> bandwidth/radiation efficiency (and hence, noise temperature) 
> performance.  The very best include choke-rings for multipath 
> suppression (Dorne-Margolin & variants), but these are costly items.  
> Miniature ceramic pucks can have pretty horrible radiation efficiency, 
> which degrades noise performance, so be careful when buying Chinese 
> cheapies.    I have actually seen commercial antennas where resistors 
> were added (before LNA) to improve antenna return loss!
> 
> On 27.01.19 14:28, Bob kb8tq wrote:
>> Hi
>> 
>> With things like the uBlox F9 now out on the market cheap …. I would go with
>> an antenna that will do L1 / L2 / L5 and work with everything that it up there.
>> You still are in the “under $100” range (delivered) for new product from China.
>> It’s a good bet that the guts of all of them are made there. It’s also a good bet
>> that they all are ceramic slab style designs.
>> 
>> Bob
>> 
>>> On Jan 26, 2019, at 11:10 PM, Denny Page via time-nuts <time-nuts at lists.febo.com> wrote:
>>> 
>>> Hi all,
>>> 
>>> I’m looking for recommendations on an antenna / splitter configuration. I currently have six GPS/GLONASS/Galileo timing devices, each with it’s own puck antenna in a window. I have an opportunity to move to a (single) roof top antenna, with a splitter to feed the individual devices, and I am looking for recommendations on which antenna and splitter people would recommend.
>>> 
>>> So far, I am looking at the following antennas:
>>> 
>>> PCTEL GNSS1-TMG-26N (https://www.pctel.com/antenna-product/global-gnss-timing-reference-antenna-gnss1-tmg-26n/)
>>> 
>>> PCTEL GNSS1-TMG-40N (https://www.pctel.com/antenna-product/global-gnss-timing-antenna-gnss1-tmg-40n/)
>>> 
>>> And the following splitters:
>>> 
>>> GPS Networking ALDCBS1x8 (https://www.gpsnetworking.com/products/aldcbs1x8)
>>> 
>>> GPS Source S18 (https://www.gpssource.com/collections/gps-splitter/products/s18-1x8-standard-gps-splitter)
>>> 
>>> The run from the antenna to the splitter will be 30-35 feet, and from the splitter to the units will be 3-5 feet. I’m wondering about the need for the 40dB vs the 26dB. I haven’t looked at any passive splitters, but even with the 40dB I’m thinking won’t offer enough to support even a 1x6 splitter.
>>> 
>>> I would appreciate any thoughts folk have to offer.
>>> 
>>> Thanks,
>>> Denny
>>> 
>>> 
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