[time-nuts] Re: GPS antenna question

[Bob kb8tq]

Hi

The most basic question is: how crazy do you want to go? This *is* TimeNuts so
crazy has very few limitations here …. :)

As mentioned in other posts, get to the point you have a clear view to the sky.
Ideally you want it clear to within 10 degrees of the horizon. You are concerned
both with blocking signals and with multipath. If things are clear to 10 degrees,
you stop using sats at 20 degrees (in the ultimate crazy approach …).

GPS for timing has turned into GNSS (multiple systems) for timing. These days
I would suggest putting up an antenna that covers multiple bands and multiple
systems. They aren’t terribly expensive from China. They do get a bit costly 
from the name brands. L1 / L2 / L5 would cover GPS. An antenna that covers
those bands likely also gets the appropriate Glonass and Galileo bands. 

Will your receiver use all the bands / all the systems? That depends on what you
use. The older cell tower gear is L1 GPS. The price of multi band / multi system
gizmos is coming down quickly. It’s a pretty good bet you will get one at some
point. 

If a 10’ mast is the only way to get a reasonable view, go for it. Maybe put a
couple guys on it to keep it from wandering a lot. 

With an antenna in a good (clear view) location, you will always have enough 
sats in view to do a proper solution for time. If you are right at the north or south
pole GPS may struggle a bit. 

Antenna gain does matter a bit. So does feed voltage. The survey folks seem
to like high gain antennas. The telecom guys seem to like low gain. You can
either put an amp in front of survey gear or an attenuator in front of a telecom
device. Neither solution is ideal. If you can, go for an antenna that is happy with
3 to 15V feed. An isolated DC feed is a simple way to handle any antenna. 

Fun !!!

Bob


> On Jul 22, 2021, at 9:05 PM, Robert DiRosario <ka3zyx at comcast.net> wrote:
> 
> If I want to use GPS for time and frequency standards, just how solidly does the antenna need to be mounted?
> The easiest and least expensive way to mount a GPS antenna would be up on two 10' TV mast sections, but that
> would move around a bit in the wind.  Maybe two or three inches.  Or do I need to do better?  All of the "easy" or
> "good" spots in my yard already have amateur radio antennas.
> 
> A second question, and it may very between different GPS receivers, how to they get the time?  Do they just take one signal
> with a good S/N number and correct for the distance from that satellite, or do something more complicated with several signals?
> 
> Thanks
> Robert
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