[time-nuts] Advice on sighting a roof mounted gps area please

Bob Camp kb8tq at n1k.org
Sun Oct 12 18:29:14 EDT 2014


Many years ago, we got dinged on customer visit when they spotted our GPS antenna array on the roof. The claim made at the time was that anything under 20’  spacing was counterproductive. I’ve seen numbers like 5, 8, 10,15 and 25 feet mentioned by different people at different times. 

The problems seem to be:

1) You have an amp in the antenna, like it or not, the antenna (and it’s coax) are not 100% shielded. They re-radiate.
2) The antenna structure (mast etc) is a reflector and you get multi-path.
3) The GPS solution does not vary enough over a short distance for a “second opinion” to be useful
4) Gear on the other end of the antenna could re-radiate. (number 4 on the list for an obvious reason … = I don’t believe it)

The first one on the list is what they dinged us on. Since it was their antenna, we sort of figured they knew something about what it did or did not do. The other three get mentioned here and there.


On Oct 12, 2014, at 5:07 PM, Hal Murray <hmurray at megapathdsl.net> wrote:

> kb8tq at n1k.org said:
>> If you are going to get any benefit from multiple antennas, you want to
>> space them as far apart as possible. You are better off with one antenna and
>> a splitter than with two close spaced antennas.  
> Does anybody have data?  How would I measure it?
> Where is the knee?  I assume the distance is measured in wavelengths.  Is it 
> 1, 10, ...?
> In a related area, does anybody have data that correlates with rain? (or 
> fog/mist)
> -- 
> These are my opinions.  I hate spam.
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