[time-nuts] Antennas, roofs

WB6BNQ wb6bnq at cox.net
Wed Feb 18 00:49:26 UTC 2009

Hi Hal,

A metal roof is generally used for those areas that have heavy snow. Such a roof
would be disastrous for the GPS if the antenna is low on top of the roof because
of reflections.  A metal roof would be harder to seal, I would think, for holes
drilled through it.  Also a metal roof can be quite slippery and dangerous for
someone climbing around on it.

The composition roof, at least, provides a less slippery surface and may provide
less reflections.  Although I would suspect that one would want to mount the
antenna at least 10 feet above the roof surface, if not higher based upon
surrounding objects like trees and so forth.

If there is a header section above the top of the wall line (i.e., in the roof
area), you may want to consider passing the pipe horizontally through the header
instead of making yet another hole for leakage in your roof.  Radio Shack use to
carry brackets for side mounting a pole along side the wall.  Two such brackets
mounted ten feet apart would provide plenty of stability for small antennas, even
including small VHF/UHF bean antennas.  Radio Shack also use to have metal
antenna poles that would stack end to end and give the ability to have any given
length (within reason).

Just some thoughts.


Hal Murray wrote:

> > I really need to put in a feed through to the roof because my Z3801A
> > is struggling with an indoor antenna too; but the roof needs to get
> > replaced first...
> Speaking of antennas and roofs....
> Currently, my antennas are inside.  That's good enough most of the time.
> It's also good for providing nasty test cases to software.
> I also need a new roof.
> I'm scheming to poke a hole in the roof so I can get some antennas in a
> better position.
> If I have more than one antenna, does it matter how near eachother they are
> located?
> I'm picturing a plastic pipe that sticks up a few feet and a bracket at the
> base that has the right magic angle to match the pitch of my roof.  The pipe
> would screw or glue into the bracket.  The bracket would get screwed to the
> roof over a hole.   The cables would go through the hole and up inside the
> pipe.
> I haven't worked out the details for the top of the pipe yet.  My (handwave)
> straw man is a U turn to keep the rain out, and mount the antennas on the
> main pipe.  Maybe a T to get them out to the side.
> Do brackets like that exist?  If so, what term or brand do I google for?  I
> have a typical not-very-steep sloped roof.  Is there a standard angle?  ...
> Plan B would be to stick the pipe through the roof and attach it inside to
> the side of a rafter.  I assume the roofers can treat it like a plumbing vent
> pipe.
> A slightly crazy idea...  Has anybody poked antennas up inside a skylight?
> I'm thinking of the setup which has a hole in the ceiling of a room, a box
> from that hole through the attic space up to and through the roof, and a
> plastic dome on top.  A shelf or bracket on the inside of the box would get
> the antennas almost on the outside.
> I've seen ads for metal roofs/shingles, the claimed advantage being long life
> which is attractive to me.  I assume they would be a disaster for antennas
> inside.  What about outside, slightly above the roof?  I'd expect bad things,
> but maybe there is some way to turn it into an advantage.
> --
> These are my opinions, not necessarily my employer's.  I hate spam.
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