[time-nuts] Mounting GPS Antenna on Steel Roof

Brooke Clarke brooke at pacific.net
Tue Mar 4 08:41:16 UTC 2008


Hi Matthew:

Some antennas are receptive to signals coming up from below.

Since the signal is circularly polarized the first reflection is supposed to be 
down something like 20 dB, but the second reflection will be much stronger, so 
you would also need to look at those.

Have Fun,

Brooke Clarke
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Matthew Smith wrote:
> Hi Folks
> 
> Further to the cable splicing thread, I have been having a discussions
> off-list with Didier regarding the placement of my antennas on the ridge
> cap of my roof.
> 
> There is certain concern that I may have issues with reflections - can
> anyone confirm whether or not this is the case?
> 
> Here is a terrible diagram (I cannot for the life of me figure out how
> to draw solid, straight lines with the Gimp) of the proposed installation:
> 
> <http://www.smiffysplace.com/files/antenna_diagram.jpg>
> 
> The ridge runs just about 15 degrees of an East-West line, is the
> highest ridge on the building and is the highest point for some distance
> (there are trees 80m to the South), barring a vertical phased array VHF
> TV antenna.
> 
> I can't really see how a signal striking the roof would reach the
> antenna, working on the basis of angle of refection = angle of incidence.
> 
> Is this installation likely to case me any problems?  I am rather short
> on other options due to the presence of steel sheds and fences.  Getting
> the antenna clear of all of these would probably require something like
> a 100m+ cable, either buried or strung overhead, neither of which is
> practical (nor the cable length).
> 
> The cable run from the ridge to my office works out at about 10m.  I
> will have a redundant antenna a couple of metres along the ridge from
> the main, disconnected.  If antenna #1 were to fail, I would just unplug
> the antenna extension cable in the loft from #1 and connect to antenna #2.
> 
> I have spotted a splitter on eBay that is good for 10-1880MHz and
> includes power passing on one output - I guess that this means I am
> still able to power the active antenna as normal provided that at a
> receiver is connected to that output.
> 
> Any comments on this would be much appreciated.
> 
> Cheers
> 
> M
> 




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