[time-nuts] Practical Survey-In Accuracy?

[Dave M]

Attila Kinali wrote:
> On Thu, 28 Aug 2014 06:30:14 -0700
> Bob Stewart <bob at evoria.net> wrote:
>
>> Is wood, nails, and asphalt shingle really that big of a problem at
>> these frequencies? The antenna is within 2 ft of the highest point
>> of the roof.
>
> Consider this: A lot of people complain about the reflections caused
> by trees. But what is a tree? It's mostly air and a few leaves, with
> a branch here and there.
>
> Also: 60cm is less than 2λ. ie the roof is in the near field of the
> antenna, where everything causes a change of the antenna behaviour
> (resonance frequency, radiation pattern, phase centre etc)
>
> Depending on what you do with the GPS signal, you might or might
> not care about that. If you are a nutty time-nut and want to
> wring out ever last bit of jitter out of your PPS, then you
> will care about the effect of the roof.
>
>
> Attila Kinali


In light of these posts about antennae and reflections, etc., I have a 
similar question.  I'm planning to move my workbench out of my attached 
garage into a separate garage building.  The new garage is about 24' x 36', 
and has a metal roof.  My plan is to mount my GPS antenna atop a metal pipe 
mounted at the peak at the end of the gable roof.
How far above the metal roof should I mount the antenna so reflections will 
be minimized, at least to the point of diminishing returns?
The antenna will have a pretty good view of the sky from that location.  Any 
other issues that I should be aware of when dealing with a metal roof?

Thanks,
Dave M