[time-nuts] Re: GPS antenna question

[Björn]

Hi Robert,

Antenna mounting... it kind of depends. First priority is having a good unobstructed sky view.  (Imagine) lying on your back watching the sky, or stars at night. If there are only minimal obstructions down low in elevation along the horizon you have a perfect sky view. Another criteria is avoiding multi path. Having a close high rise building with a reflective wall will make your receiver get a strong reflected signal sometimes. This could be hard for the receiver to distinguish from the direct line of sight signal and cause position/time errors.

Modern high sensitive receivers, they work fine with less perfect sky view.

There is no need to elevate your GPS antenna if you already have a good sky view from a lower height.

Test your antenna site by watching SNR at your preferred site. There are control software (like Lady Heather) that will plot az/el vs SNR and by running that for a day you will get good information on how your receiver likes that antenna spot.

/Björn 

Sent from my iPhone

> On 23 Jul 2021, at 03:01, 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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